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    9:     <h2>Chapter 10</h2>
   10:     <h1><a name="77061"></a> RDF, RDF Tools, and the Content
   11:     Model</h1>
   12:     <p><a href="ch09.html#77034">Chapter 9</a> introduced the
   13:     Resource Description Framework (RDF) as the basis for building
   14:     display data in the interface, where XUL templates take
   15:     RDF-based data and transform it into regular widgets. But RDF
   16:     is used in many other more subtle ways in Mozilla. In fact, it
   17:     is the technology Mozilla uses for much of its own internal
   18:     data handling and manipulation.</p>
   19:     <p>RDF is, as its name suggests, a framework for integrating
   20:     many types of data that go into the browser, including
   21:     bookmarks, mail messages, user profiles, IRC channels, new
   22:     Mozilla applications, and your collection of sidebar tabs. All
   23:     these items are sets of data that RDF represents and
   24:     incorporates into the browser consistently. RDF is used
   25:     prolifically in Mozilla, which is why this chapter is so
   26:     dense.</p>
   27:     <p>This chapter introduces RDF, provides some detail about how
   28:     Mozilla uses RDF for its own purposes, and describes the RDF
   29:     tools that are available on the Mozilla platform. The chapter
   30:     includes information on special JavaScript libraries that make
   31:     RDF processing much easier, and on the use of RDF in manifests
   32:     to represent JAR file contents and cross-platform installation
   33:     archives to Mozilla.</p>
   34:     <p>Once you understand the concepts in this chapter, you can
   35:     make better use of data and metadata in your own application
   36:     development.</p>
   37:     <h2><a name="77062"></a> RDF Basics</h2>
   38:     <p>RDF has two 
   39:     <!--INDEX RDF (Resource Description Framework):overview -->
   40:     parts: the <i>RDF Data Model</i> and the <i>RDF Syntax</i> (or
   41:     Grammar). The RDF Data Model is a graph with nodes and arcs,
   42:     much like other data graphs. More specifically, it's a
   43:     <i>labeled-directed</i> graph. All nodes and arcs have some
   44:     type of label (i.e., an identifier) on them, and arcs point
   45:     only in one direction.</p>
   46:     <p>The RDF Syntax determines how the RDF Data Model is
   47:     represented, typically as a special kind of XML. Most XML
   48:     specifications define data in a tree-like model, such as XUL
   49:     and XBL. But the RDF Data Model cannot be represented in a true
   50:     tree-like structure, so the RDF/XML syntax includes properties
   51:     that allow you to represent the same data in more than one way:
   52:     elements can appear in different orders but mean the same
   53:     thing, the same data can be represented as a child element or
   54:     as a parent attribute, and data have indirect meanings. The
   55:     meaning is not inherent in the structure of the RDF/XML itself;
   56:     only the relationships are inherent. Thus, an RDF processor
   57:     must make sense of the represented RDF data. Fortunately, an
   58:     excellent RDF processor is integrated into Mozilla.</p>
   59:     <h3><a name="77063"></a> RDF Data Model</h3>
   60:     <p>Three 
   61:     <!--INDEX RDF (Resource Description Framework):data model --> 
   62:     <!--INDEX data model (RDF) --> different types of RDF objects
   63:     are the basis for all other RDF concepts: <i>resources</i>,
   64:     <i>properties</i>, and <i>statements</i>. Resources 
   65:     <!--INDEX resources:RDF --> are any type of data described by
   66:     RDF. Just as an English sentence is comprised of subjects and
   67:     objects, the resources described in RDF are typically subjects
   68:     and objects of RDF statements. Consider this example:</p>
   69:     <blockquote>
   70:       Eric wrote a book.
   71:     </blockquote>
   72:     <p><i>Eric</i> is the subject of this statement, and would
   73:     probably be an RDF resource in an RDF statement. <i>A book</i>,
   74:     the object, might also be a resource because it represents
   75:     something about which we might want to say more in RDF-for
   76:     example, the book is a computer book or the book sells for
   77:     twenty dollars. A property <!--INDEX properties:RDF --> is a
   78:     characteristic of a resource and might have a relationship to
   79:     other resources. In the example, the book was written by Eric.
   80:     In the context of RDF, <i>wrote</i> is a property of the
   81:     <i>Eric</i> resource. An RDF statement is a resource, a
   82:     property, and another resource grouped together. Our example,
   83:     made into an RDF statement, might look like this:</p>
   84:     <blockquote>
   85:       (Eric) wrote (a book)
   86:     </blockquote>
   87:     <p>Joining RDF statements makes an entire RDF graph.</p>
   88:     <blockquote>
   89:       <div class="c21">
   90:         NOTE
   91:       </div>
   92:       <p>We are describing the RDF data model here, not the RDF
   93:       syntax. The RDF syntax uses XML to describe RDF statements
   94:       and the relationship of resources.</p>
   95:     </blockquote>
   96:     <p>As mentioned in the introduction, the RDF content model is a
   97:     <i><!--INDEX labeled-directed graphs (RDF) -->
   98:     labeled-directed</i> graph, which means that all relationships
   99:     expressed in the graph are unidirectional, as displayed in <a
  100:     href="#77002">Figure 10-1</a>.</p>
  101:     <div class="c22">
  102:       <img src="foo.gif">
  103:     </div>
  104:     <p><i>Figure 10-1: <a name="77002"></a></i> <i>Simple
  105:     labeled-directed graph</i></p>
  106:     <p>A resource can contain either a URI or a literal. The root
  107:     resource might have a 
  108:     <!--INDEX URIs (Universal Resource Identifiers):RDF --> URI,
  109:     for example, from which all other resources in the graph
  110:     descend. The RDF processor continues from the root resource
  111:     along its properties to other resources in the graph until it
  112:     runs out of properties to traverse. RDF processing terminates
  113:     at a <!--INDEX literals:RDF --> literal, which is just what it
  114:     sounds like: something that stands only for itself, generally
  115:     represented by a string (e.g., "book," if there were no more
  116:     information about the book in the graph). A literal resource
  117:     contains only non-RDF data. A literal is a terminal point in
  118:     the RDF graph.</p>
  119:     <p>For a resource to be labeled, it must be addressed through a
  120:     universal resource identifier (URI). This address must be a
  121:     unique string that designates what the resource is. In
  122:     practice, most resources don't have identifiers because they
  123:     are not nodes on the RDF graph that are meant to be accessed
  124:     through a URI. <a href="#77004">Figure 10-2</a> is a modified
  125:     version of <a href="#77002">Figure 10-1</a> that shows
  126:     <i>Eric</i> as a resource identifier and <i>book</i> as a
  127:     literal.</p>
  128:     <div class="c22">
  129:       <img src="foo.gif">
  130:     </div>
  131:     <p><i>Figure 10-2: <a name="77004"></a></i> <i>Resource to
  132:     literal relationship</i></p>
  133:     <p>Resources can have any number of properties, which
  134:     themselves differ. In <a href="#77004">Figure 10-2</a>,
  135:     <i>wrote</i> is a property of <i>Eric</i>. However, resources
  136:     can also have multiple properties, as shown in <a href=
  137:     "#77006">Figure 10-3</a>.</p>
  138:     <div class="c22">
  139:       <img src="foo.gif">
  140:     </div>
  141:     <p><i>Figure 10-3: <a name="77006"></a></i> <i>RDF Graph with
  142:     five nodes</i></p>
  143:     <p>The RDF graph in <a href="#77006">Figure 10-3</a> has five
  144:     nodes, two resources, and three literals. If this graph were
  145:     represented in XML, it would probably have three different XML
  146:     namespaces inside of it: RDF/XML, a <i>book</i> XML
  147:     specification, and a <i>computer</i> XML specification. In
  148:     English, the graph in <a href="#77006">Figure 10-3</a> might be
  149:     expressed as follows:</p>
  150:     <blockquote>
  151:       Eric wrote a book of unknown information. Eric's computer is
  152:       700 MHz and has an Athlon CPU.
  153:     </blockquote>
  154:     <p>Note that if Eric wrote a poem and a book, it would be
  155:     possible to have two <i>wrote</i> properties for the same
  156:     resource. Using the same property to point to separate
  157:     resources is confusing, however. Instead, RDF containers (see
  158:     the section <a href="#77069">"RDF containers</a>," later in
  159:     this chapter) are the best way to organize data that would
  160:     otherwise need a single property to branch in this way.</p>
  161:     <h4><a name="77064"></a> RDF URIs relating to namespaces</h4>
  162:     <p>The 
  163:     <!--INDEX RDF (Resource Description Framework):data model:URIs -->
  164:     <!--INDEX data model (RDF):URIs --> <!--INDEX URIs (Universal 
  165:     Resource Identifiers):RDF:namespaces --> 
  166:     <!--INDEX namespaces:RDF, URIs and --> URIs used in RDF can be
  167:     part of the element namespace. (See <a href=
  168:     "ch02.html#77053">"The XUL Namespace" in Chapter 2</a> and in
  169:     <a href="ch07.html#77031">"Namespaces and XBL" in Chapter 7</a>
  170:     for more information about XML namespaces.) This use is
  171:     especially true for properties. Some namespaces can be created
  172:     from previous examples:</p>
  173: <pre>
  174: xmlns:rdf="<a href=
  175: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#"
  176: xmlns:book="<a href=
  177: "http://www.oreilly.com/rdf">http://www.oreilly.com/rdf</a>#"
  178: xmlns:comp="my.computer.hardware#"
  179: </pre>
  180:     <p>When you use namespaces, the graph looks much different, as
  181:     shown in <a href="#77008">Figure 10-4</a>.</p>
  182:     <div class="c22">
  183:       <img src="foo.gif">
  184:     </div>
  185:     <p><i>Figure 10-4: <a name="77008"></a></i> <i>Namespaces
  186:     applied to Figure 10-3</i></p>
  187:     <blockquote>
  188:       <div class="c21">
  189:         NOTE
  190:       </div>
  191:       <p>The resource identifier is often displayed in a URL format
  192:       too, but it shouldn't use the same namespace URL as the
  193:       RDF/XML file. The URL typically tries to describe a unique
  194:       object, such as <i><a href=
  195:       "http://my.jar-of-flies.com">http://my.jar-of-flies.com</a></i>.</p>
  196:     </blockquote>
  197:     <h4><a name="77065"></a> RDF triples: subject, predicate, and
  198:     object</h4>
  199:     <p>A triple <!--INDEX statements, RDF, triples --> 
  200:     <!--INDEX triples:RDF statements --> 
  201:     <!--INDEX RDF (Resource Description Framework):statements, triples -->
  202:     is a type of RDF statement. While an RDF statement can be a
  203:     loose collection of resources, properties, and literals, a
  204:     triple typically defines a tighter relationship between such
  205:     elements.</p>
  206:     <p>The first part of a triple is the <i>subject</i>. This part
  207:     is the resource described by the triple. The second part of the
  208:     triple is the <i>predicate</i>. This part is a subject's
  209:     property, a thing that joins it with something else. The third
  210:     part is the <i>object</i>, which is either a resource or a
  211:     literal.</p>
  212:     <p>RDF triples are significant because their stricter semantics
  213:     guarantee the relationship between parts. A triple is a more
  214:     formal version of the RDF statement, which is used more
  215:     broadly. In <a href="#77008">Figure 10-4</a>, all statements
  216:     are formally subject &gt; predicate &gt; object, so those
  217:     statements are triples.</p>
  218:     <h4><a name="77066"></a> RDF data model terminology</h4>
  219:     <p>When 
  220:     <!--INDEX RDF (Resource Description Framework):data model:terminology -->
  221:     <!--INDEX data model (RDF):terminology --> reading RDF
  222:     specifications, documentation, examples, and other related
  223:     material on the Internet, you can encounter a dizzying array of
  224:     terms that mean the same thing. <a href="#77020">Table 10-1</a>
  225:     should help clarify these different terms. The italicized
  226:     versions of the synonyms all do not technically mean the same
  227:     thing, but are loose synonyms whose meanings depend on the
  228:     context in which they are used.</p>
  229:     <p><i>Table 10-1: <a name="77020"></a></i> <i>Synonyms in
  230:     RDF</i></p>
  231:     <table width="100%" border="1">
  232:       <tr>
  233:         <td><b>Common term</b></td>
  234:         <td><b>Synonyms</b></td>
  235:       </tr>
  236:       <tr>
  237:         <td>Resource</td>
  238:         <td>Subject, object</td>
  239:       </tr>
  240:       <tr>
  241:         <td>Resource identifier</td>
  242:         <td>Name, (resource) URI, ID, identifier, URL, label</td>
  243:       </tr>
  244:       <tr>
  245:         <td>Properties</td>
  246:         <td>Attributes</td>
  247:       </tr>
  248:       <tr>
  249:         <td>Statement</td>
  250:         <td>Triple, tuple, binding, assertion</td>
  251:       </tr>
  252:       <tr>
  253:         <td>Subject</td>
  254:         <td>Source, resource, node, root</td>
  255:       </tr>
  256:       <tr>
  257:         <td>Predicate</td>
  258:         <td>Arc, (statement) URI, property, atom</td>
  259:       </tr>
  260:       <tr>
  261:         <td>Object</td>
  262:         <td>Value, resource, node, literal</td>
  263:       </tr>
  264:     </table>
  265:     <h3><a name="77067"></a> RDF Syntax</h3>
  266:     <p>Mozilla 
  267:     <!--INDEX RDF (Resource Description Framework):syntax:overview -->
  268:     <!--INDEX syntax, RDF:overview --> uses XML to represent RDF
  269:     data. In 1999, the W3C defined the RDF/XML specification syntax
  270:     to make it the most common way RDF is used. The RDF/XML format
  271:     is sometimes called the RDF serialization syntax because it
  272:     allows RDF models to be sent easily from one computer
  273:     application to another in a common XML format.</p>
  274:     <p>When an application reads an RDF file, the Mozilla RDF
  275:     processor builds a graphical interpretation in-memory. In this
  276:     section, you learn how to build an RDF file from scratch and
  277:     see what the graph looks like after running through Mozilla's
  278:     RDF processor.</p>
  279:     <blockquote>
  280:       <div class="c21">
  281:         NOTE
  282:       </div>
  283:       <p><tt>RDF:RDF</tt> is a common namespace representation of
  284:       RDF/XML data and is the one most frequently used in Mozilla
  285:       files. However, it can be hard to read, so this chapter uses
  286:       <tt>rdf:RDF</tt>. The W3C also used <tt>rdf:RDF</tt> in the
  287:       RDF recommendation document.</p>
  288:     </blockquote>
  289:     <h4><a name="77068"></a> Examining a simple RDF file</h4>
  290:     <p>We begin 
  291:     <!--INDEX RDF (Resource Description Framework):syntax:files -->
  292:     <!--INDEX syntax, RDF:files --> <!--INDEX files:RDF:syntax -->
  293:     with an example of an RDF file whose basic layout and simple
  294:     syntax can be a model for the more advanced data introduced
  295:     later. The RDF file shown in <a href="#77026">Example 10-1</a>
  296:     is a list of three types of "flies," with the context of those
  297:     "flies" inside a "jar." <a href="#77026">Example 10-1</a> also
  298:     contains a namespace that defines these types of flies and
  299:     shows the <tt>rdf</tt> and <tt>fly</tt> XML intertwined.</p>
  300:     <p><i>Example 10-1: <a name="77026"></a></i> <i>Simple RDF file
  301:     with "fly" namespace</i></p>
  302: <pre>
  303:    &lt;?xml version="1.0"?&gt;
  304:    &lt;rdf:RDF
  305:       xmlns:rdf="<a href=
  306: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#"
  307:       xmlns:fly="<a href=
  308: "http://xfly.mozdev.org/fly-rdf">http://xfly.mozdev.org/fly-rdf</a>#"&gt;
  309:      &lt;rdf:Description about="<a href=
  310: "http://my.jar-of-flies.com">http://my.jar-of-flies.com</a>"&gt;
  311:        &lt;fly:types&gt;
  312:          &lt;rdf:Bag&gt;
  313:            &lt;rdf:li&gt;
  314:              &lt;rdf:Description fly:name="Horse"/&gt;
  315:            &lt;/rdf:li&gt;
  316:            &lt;rdf:li&gt;
  317:              &lt;rdf:Description fly:name="House"/&gt;
  318:            &lt;/rdf:li&gt;
  319:            &lt;rdf:li&gt;
  320:              &lt;rdf:Description fly:name="Fruit"/&gt;
  321:            &lt;/rdf:li&gt;
  322:          &lt;/rdf:Bag&gt;
  323:        &lt;/fly:types&gt;
  324:      &lt;/rdf:Description&gt;
  325:    &lt;/rdf:RDF&gt;
  326: </pre>
  327:     <p><tt><!--INDEX rdf\:Description element -->
  328:     &lt;rdf:Description&gt;</tt> is the tag used to outline a
  329:     resource. <a href="#77026">Example 10-1</a> shows how the
  330:     <tt>about</tt> attribute references the resource identifier and
  331:     makes this resource unique in the document. Two resources
  332:     cannot have the same <tt>about</tt> value in a document, just
  333:     as tags cannot share an <tt>id</tt> in an XML document. Both
  334:     attributes guarantee the unique nature of each element and
  335:     relationship.</p>
  336: <pre>
  337: &lt;rdf:Description about="<a href=
  338: "http://my.jar-of-flies.com">http://my.jar-of-flies.com</a>"&gt;
  339: &lt;fly:types&gt;
  340: &lt;rdf:Bag&gt;
  341: </pre>
  342:     <p><tt><a href=
  343:     "http://my.jar-of-flies.com">http://my.jar-of-flies.com</a></tt>,
  344:     is the subject shown in the previous code snippet. <i>My jar of
  345:     flies</i> is a resource definition and defines only what
  346:     <i>flies</i> are inside of the statement. The predicate, which
  347:     addresses a property in the resource, is defined by the tag
  348:     <tt>&lt;types&gt;</tt> (of the <tt><a href=
  349:     "http://xfly.mozdev.org/fly-rdf">http://xfly.mozdev.org/fly-rdf</a>#</tt>
  350:     namespace).</p>
  351:     <p>The final part of the statement, the object, is the actual
  352:     data of the predicate and a container of type bag. The
  353:     container is an RDF resource that "holds," or points to, a
  354:     collection of other resources. In the next section, container
  355:     types are discussed in depth. <a href="#77010">Figure 10-5</a>
  356:     illustrates how the triple originates from the root subject and
  357:     includes the container object.</p>
  358:     <div class="c22">
  359:       <img src="foo.gif">
  360:     </div>
  361:     <p><i>Figure 10-5: <a name="77010"></a></i> <i>The first
  362:     statement of the graph, with labeled parts</i></p>
  363:     <p>In this case, an RDF statement is extracted from the
  364:     example, but no useful data is reached. Little can be done with
  365:     an empty RDF container, and two more steps are needed to reach
  366:     literals that contain names of the flies.</p>
  367:     <h4><a name="77069"></a> RDF containers</h4>
  368:     <p>Containers 
  369:     <!--INDEX RDF (Resource Description Framework):containers --> 
  370:     <!--INDEX containers:RDF --> are a list of resources or
  371:     literals. They are a form of RDF 
  372:     <!--INDEX resources:RDF:containers --> resource. There are
  373:     three different container types: <tt>bag</tt>,
  374:     <tt>sequence</tt>, and <tt>alternative</tt>. <tt>Bag</tt> is an
  375:     unordered list of items, whereas <tt>sequence</tt> is an
  376:     ordered list of items. They both allow duplicate values.
  377:     <tt>Alternative</tt> is a list of values that could replace a
  378:     particular property in a resource. <tt>Sequence</tt> is the
  379:     most popular container for use in Mozilla applications because
  380:     it frequently uses ordered lists of data. A container's
  381:     graphical definition is an entire separate statement about its
  382:     type and the items it contains. In <a href="#77012">Figure
  383:     10-6</a>, you can see the type of the container defined in the
  384:     RDF statement with the property <tt>rdf:type</tt>. The
  385:     remaining properties are the container's items.</p>
  386:     <div class="c22">
  387:       <img src="foo.gif">
  388:     </div>
  389:     <p><i>Figure 10-6: <a name="77012"></a></i> <i>The second
  390:     statement of the graph, with labeled parts</i></p>
  391:     <p>Once the container is defined, you can examine its
  392:     collection of elements. At this point in the RDF code, direct
  393:     comparisons can again be made from the code to the graph:</p>
  394: <pre>
  395: &lt;rdf:Bag&gt;
  396: &lt;rdf:li&gt;
  397: &lt;rdf:Description ...
  398: </pre>
  399:     <p>Here, the <tt><!--INDEX rdf\:li tag --> &lt;rdf:li&gt;</tt>
  400:     tag is similar to the <tt>&lt;li&gt;</tt> tag in HTML, which
  401:     stands for "list item." Moving from code to graph, the new
  402:     representation is shown in <a href="#77012">Figure
  403:     10-6</a>.</p>
  404:     <p>In <a href="#77012">Figure 10-6</a>, the subject is the
  405:     instance of the container. This statement does not begin from
  406:     <tt>rdf:Bag</tt> because that resource is only a type
  407:     definition. The actual items in the container originate from
  408:     the instance created in memory by any RDF processor, including
  409:     Mozilla's.</p>
  410:     <blockquote>
  411:       <div class="c21">
  412:         NOTE
  413:       </div>
  414:       <p>Mozilla's RDF processor fills in the <tt>rdf:*(1)</tt> of
  415:       the resource identifier in <a href="#77012">Figure 10-6</a>
  416:       with a hashed value. The same is true for the container's
  417:       resource identifier. The actual values come out as something
  418:       like <tt>rdf:#$0mhkm1</tt>, though the values change each
  419:       time the RDF document is loaded.</p>
  420:     </blockquote>
  421:     <p>Objects inside of the container have 
  422:     <!--INDEX properties:RDF:containers --> properties identified
  423:     automatically as <tt>rdf:_1</tt>, <tt>rdf:_2</tt>, etc., as
  424:     defined by the RDF model specification. However, RDF
  425:     applications such as Mozilla may use different identifiers to
  426:     differentiate list objects.</p>
  427:     <h4><a name="77070"></a> Literals</h4>
  428:     <p>The final 
  429:     <!--INDEX RDF (Resource Description Framework):literals -->
  430:     statement in <a href="#77026">Example 10-1</a> allows the
  431:     predicate to reach the text data, the literal "horse" shown in
  432:     <a href="#77014">Figure 10-7</a>. Note that the <tt>about</tt>
  433:     reference on the <tt>Description</tt> is fictitious RDF, but it
  434:     demonstrates the difference between a resource and a
  435:     literal.</p>
  436: <pre>
  437: &lt;rdf:Description about="rdf:*(1)" fly:name="Horse"/&gt;
  438: </pre>
  439:     <div class="c22">
  440:       <img src="foo.gif">
  441:     </div>
  442:     <p><i>Figure 10-7: <a name="77014"></a></i> <i>The third
  443:     statement of the graph, with labeled parts</i></p>
  444:     <p>The previous RDF 
  445:     <!--INDEX RDF (Resource Description Framework):syntax:shorthand -->
  446:     <!--INDEX syntax, RDF:shorthand --> code for the literal is
  447:     syntactic shorthand. Using this type of shortcut can make RDF
  448:     much easier to read. The previous code snippet is the same as
  449:     the longer and more cumbersome one shown here:</p>
  450: <pre>
  451: &lt;rdf:Description about="rdf:*(1)"&gt;
  452: &lt;fly:name&gt;Horse&lt;/fly:name&gt;
  453: &lt;/rdf:Description&gt;
  454: </pre>
  455:     <p>The shorthand version of this statement can be useful when
  456:     you have a lot of data or when you want to use one syntax to
  457:     show all relationships in the graph.</p>
  458:     <h4><a name="77071"></a> The RDF syntax and RDF graphs</h4>
  459:     <p><a href="#77016">Figure 10-8</a> shows the entire RDF graph
  460:     for the RDF file in <a href="#77026">Example 10-1</a>. This
  461:     graph was compiled by combining the concepts you've seen in
  462:     Figures 10-5 through 10-7.</p>
  463:     <p>As you can see, the statements fit together quite nicely.
  464:     Four resources originate from the container, and one is the
  465:     container type definition. The other two properties are
  466:     numbered according to their order in the RDF file.</p>
  467:     <div class="c22">
  468:       <img src="foo.gif">
  469:     </div>
  470:     <p><i>Figure 10-8: <a name="77016"></a></i> <i>The full
  471:     graph</i></p>
  472:     <h3><a name="77072"></a> Building an RDF File from Scratch</h3>
  473:     <p>Now that 
  474:     <!--INDEX RDF (Resource Description Framework):files:creating -->
  475:     <!--INDEX files:RDF:creating --> you understand the basic
  476:     principles of a simple RDF file, this section steps through the
  477:     creation of an RDF file from information found in regular
  478:     text:</p>
  479:     <blockquote>
  480:       There is a jar with the name urn:root. Inside of it there are
  481:       two types of flies listed as House and Horse. There are three
  482:       Horse flies. The Face Fly, coded in green, is officially
  483:       identified as "musca autumnalis". The Stable Fly, coded in
  484:       black, has the identification "stomoxys_calcitrans." The
  485:       red-coded Horn Fly, located in Kansas, is identified as
  486:       "haematobia_irritans." There are also three house flies.
  487:       "musca_domestica," coded in brown, has the name "Common House
  488:       Fly." A gray fly named "Carrion Fly" has the ID "sarcophagid"
  489:       and is found globally. Finally, The "Office Fly," coded with
  490:       white, is prevalent in the Bay Area.
  491:     </blockquote>
  492:     <p>You can use the techniques described here to model the data
  493:     you want in your application: spreadsheet-like rosters of
  494:     people, family trees, or catalogs of books or other items.</p>
  495:     <h4><a name="77073"></a> Identify namespaces</h4>
  496:     <p>The new 
  497:     <!--INDEX namespaces:identifying, creating RDF files --> 
  498:     <!--INDEX RDF (Resource Description Framework):files:identifying namespaces -->
  499:     <!--INDEX files:RDF:identifying namespaces --> RDF file will
  500:     have three namespaces including the RDF namespace. The result
  501:     is two different data types that are connected in an RDF graph.
  502:     For the sake of the example, one namespace is not in the
  503:     standard URL format. Here is how the RDF file namespaces are
  504:     set up:</p>
  505: <pre>
  506: &lt;?xml version="1.0"?&gt;
  507: &lt;rdf:RDF xmlns:rdf="<a href=
  508: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#"
  509: xmlns:fly="<a href=
  510: "http://xfly.mozdev.org/fly-rdf">http://xfly.mozdev.org/fly-rdf</a>#"
  511: xmlns:location="fly-location#"&gt;
  512: &lt;/rdf:RDF&gt;
  513: </pre>
  514:     <h4><a name="77074"></a> Root resource</h4>
  515:     <p>This file's <!--INDEX resources:RDF:creating files --> 
  516:     <!--INDEX root resources, RDF files --> 
  517:     <!--INDEX RDF (Resource Description Framework):files:root resources -->
  518:     <!--INDEX files:RDF:root resources --> root resource is an
  519:     <tt>urn:root</tt>, which is the conventional name for root
  520:     nodes in Mozilla's RDF files. When rendering RDF files,
  521:     defining a root node for processing the document can be
  522:     useful-especially when building templates. This root node can
  523:     be entered as the first item in the file:</p>
  524: <pre>
  525: &lt;?xml version="1.0"?&gt;
  526: &lt;rdf:RDF xmlns:rdf="<a href=
  527: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#"
  528: xmlns:fly="<a href=
  529: "http://xfly.mozdev.org/fly-rdf">http://xfly.mozdev.org/fly-rdf</a>#"
  530: xmlns:location="fly-location#"&gt;
  531: &lt;rdf:Description about="urn:root"&gt;
  532: &lt;/rdf:Description&gt;
  533: &lt;/rdf:RDF&gt;
  534: </pre>
  535:     <h4><a name="77075"></a> Root sequence</h4>
  536:     <p>Next, a <!--INDEX sequences, RDF:creating files --> 
  537:     <!--INDEX root sequences, RDF files --> 
  538:     <!--INDEX RDF (Resource Description Framework):files:root sequesces -->
  539:     <!--INDEX files:RDF:root sequesces --> generic tag needs to be
  540:     used to specify a sequence of "fly" data. As in <a href=
  541:     "#77028">Example 10-2</a>, <tt>&lt;fly:list&gt;</tt> is used as
  542:     a list of fly types. This tag is a generic name because of the
  543:     way XUL templates process lists of RDF data. If a list of data
  544:     has sublists, as in the following examples, then they must use
  545:     the same tag name to recurse correctly for the data they
  546:     contain.</p>
  547:     <p><a href="#77028">Example 10-2</a> represents all the
  548:     information given in the first paragraph of the text example:
  549:     "There is a jar set up with the name <i>urn:root</i>. Inside of
  550:     it there are two types of flies, listed as House and
  551:     Horse."</p>
  552:     <p><i>Example 10-2: <a name="77028"></a></i> <i>RDF root
  553:     sequence</i></p>
  554: <pre>
  555:  &lt;?xml version="1.0"?&gt;
  556:  &lt;rdf:RDF xmlns:rdf="<a href=
  557: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#"
  558:           xmlns:fly="<a href=
  559: "http://xfly.mozdev.org/fly-rdf">http://xfly.mozdev.org/fly-rdf</a>#"
  560:           xmlns:location="fly-location#"&gt;
  561:    &lt;rdf:Description about="urn:root"&gt;
  562:      &lt;fly:list&gt;
  563:        &lt;rdf:Seq&gt;
  564:          &lt;rdf:li&gt;
  565:            &lt;rdf:Description ID="House" fly:label="House"/&gt;
  566:          &lt;/rdf:li&gt;
  567:          &lt;rdf:li&gt;
  568:            &lt;rdf:Description ID="Horse" fly:label="Horse"/&gt;
  569:          &lt;/rdf:li&gt;
  570:        &lt;/rdf:Seq&gt;
  571:      &lt;/fly:list&gt;
  572:    &lt;/rdf:Description&gt;
  573:  &lt;/rdf:RDF&gt;
  574: </pre>
  575:     <p>An RDF sequence resides with its list of resources inside
  576:     <tt>&lt;fly:list&gt;</tt>. Here, shorthand RDF specifies a
  577:     label with the <tt>fly:label</tt> attribute. The <tt>ID</tt>
  578:     attribute within this sequence is actually a pointer to the
  579:     main definition of the resource described by an <tt>about</tt>
  580:     attribute of the same value. The <tt>about</tt> attribute
  581:     includes a <tt>#</tt> in its identifier, much like HTML anchors
  582:     use <tt>&lt;a href="#frag"&gt;</tt> to refer to <tt>&lt;a
  583:     name="frag"&gt;</tt>. For example, <tt>ID="Horse"</tt> points
  584:     to <tt>about="#Horse</tt>" elsewhere in the file, allowing you
  585:     to add to the description of any element with new properties
  586:     and resources.</p>
  587:     <h4><a name="77076"></a> Secondary sequences and literals</h4>
  588:     <p>The <!--INDEX sequences, RDF:creating files --> 
  589:     <!--INDEX secondary sequences, RDF files --> 
  590:     <!--INDEX RDF (Resource Description Framework):files:secondary sequesces -->
  591:     <!--INDEX files:RDF:secondary sequesces --> <tt>Horse</tt> and
  592:     <tt>House</tt> resources need to be defined next. <a href=
  593:     "#77030">Example 10-3</a> shows the creation of <tt>Horse</tt>
  594:     from the second paragraph. The process for creating
  595:     <tt>House</tt> is almost identical.</p>
  596:     <p><i>Example 10-3: <a name="77030"></a></i> <i>The Horse
  597:     sequence</i></p>
  598: <pre>
  599:  &lt;rdf:Description about="#Horse"&gt;
  600:      &lt;fly:list&gt;
  601:        &lt;rdf:Seq&gt;
  602:          &lt;rdf:li&gt;
  603:            &lt;rdf:Description about="musca_autumnalis"
  604:                             fly:label="Face fly"
  605:                             fly:color="green"/&gt;
  606:          &lt;/rdf:li&gt;
  607:          &lt;rdf:li&gt;
  608:            &lt;rdf:Description about="stomoxys_calcitrans"
  609:                             fly:label="Stable Fly"
  610:                             fly:color="black"/&gt;
  611:          &lt;/rdf:li&gt;
  612:          &lt;rdf:li&gt;
  613:            &lt;rdf:Description about="haematobia_irritans"
  614:                             fly:label="Horn Fly"
  615:                             fly:color="red"
  616:                             location:location="Kansas"/&gt;
  617:          &lt;/rdf:li&gt;
  618:        &lt;/rdf:Seq&gt;
  619:      &lt;/fly:list&gt;
  620:    &lt;/rdf:Description&gt;
  621: </pre>
  622:     <p>Here the shorthand RDF definition continues to use only the
  623:     attributes. Again, a <tt>&lt;fly:list&gt;</tt> is defined and
  624:     the items inside it are listed. The listed values have multiple
  625:     attribute values, all of which are RDF literals. In longhand
  626:     with RDF showing all literals, the last item would be written
  627:     out as follows:</p>
  628: <pre>
  629: &lt;rdf:li&gt;
  630: &lt;rdf:Description about="haematobia_irritans "&gt;
  631: &lt;fly:label&gt;Horn Fly&lt;/fly:label&gt;
  632: &lt;fly:color&gt;red&lt;/fly:color&gt;
  633: &lt;location:location&gt;Kansas&lt;/location:location&gt;
  634: &lt;/rdf:Description&gt;
  635: &lt;/rdf:li&gt;
  636: </pre>
  637:     <p>The two different namespace literals are both resource
  638:     attributes. <tt>haematobia_irritans</tt> is used as the
  639:     resource identifier because it is a unique value among all
  640:     data.</p>
  641:     <p>Laying out the data in the same pattern gives you the final,
  642:     full RDF file in <a href="#77032">Example 10-4</a>.</p>
  643:     <p><i>Example 10-4: <a name="77032"></a></i> <i>Entire RDF
  644:     file</i></p>
  645: <pre>
  646:  &lt;?xml version="1.0"?&gt;
  647:  &lt;rdf:RDF xmlns:rdf="<a href=
  648: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#"
  649:           xmlns:fly="<a href=
  650: "http://xfly.mozdev.org/fly-rdf">http://xfly.mozdev.org/fly-rdf</a>#"
  651:           xmlns:location="fly-location#"&gt;
  652:    &lt;rdf:Description about="urn:root"&gt;
  653:      &lt;fly:list&gt;
  654:        &lt;rdf:Seq&gt;
  655:          &lt;rdf:li&gt;
  656:            &lt;rdf:Description ID="House" fly:label="House"/&gt;
  657:          &lt;/rdf:li&gt;
  658:          &lt;rdf:li&gt;
  659:            &lt;rdf:Description ID="Horse" fly:label="Horse"/&gt;
  660:          &lt;/rdf:li&gt;
  661:        &lt;/rdf:Seq&gt;
  662:      &lt;/fly:list&gt;
  663:    &lt;/rdf:Description&gt;
  664:    &lt;rdf:Description about="#Horse"&gt;
  665:      &lt;fly:list&gt;
  666:        &lt;rdf:Seq&gt;
  667:          &lt;rdf:li&gt;
  668:            &lt;rdf:Description about="musca_autumnalis"
  669:                             fly:label="Face fly"
  670:                             fly:color="green"/&gt;
  671:          &lt;/rdf:li&gt;
  672:          &lt;rdf:li&gt;
  673:            &lt;rdf:Description about="stomoxys_calcitrans"
  674:                             fly:label="Stable Fly"
  675:                             fly:color="black"/&gt;
  676:          &lt;/rdf:li&gt;
  677:          &lt;rdf:li&gt;
  678:            &lt;rdf:Description about="haematobia_irritans"
  679:                             fly:label="Horn Fly"
  680:                             fly:color="red"
  681:                             location:location="Kansas"/&gt;
  682:          &lt;/rdf:li&gt;
  683:        &lt;/rdf:Seq&gt;
  684:      &lt;/fly:list&gt;
  685:    &lt;/rdf:Description&gt;
  686:    &lt;rdf:Description about="#House"&gt;
  687:      &lt;fly:list&gt;
  688:        &lt;rdf:Seq&gt;
  689:          &lt;rdf:li&gt;
  690:            &lt;rdf:Description about="musca_domestica"
  691:                             fly:label="Common House Fly"
  692:                             fly:color="brown"/&gt;
  693:          &lt;/rdf:li&gt;
  694:          &lt;rdf:li&gt;
  695:            &lt;rdf:Description about="sarcophagid"
  696:                             fly:label="Carrion Fly"
  697:                             fly:color="gray"
  698:                             location:location="Worldwide"/&gt;
  699:          &lt;/rdf:li&gt;
  700:          &lt;rdf:li&gt;
  701:            &lt;rdf:Description about="musca_oficio"
  702:                             fly:label="Office Fly"
  703:                             fly:color="white"
  704:                             location:location="California, Bay Area"/&gt;
  705:          &lt;/rdf:li&gt;
  706:        &lt;/rdf:Seq&gt;
  707:      &lt;/fly:list&gt;
  708:    &lt;/rdf:Description&gt;
  709:  &lt;/rdf:RDF&gt;
  710: </pre>
  711:     <p><a href="#77032">Example 10-4</a> shows the RDF data used in
  712:     several template examples in <a href="ch09.html#77034">Chapter
  713:     9</a>. <a href="ch09.html#77022">Example 9-4</a> includes the
  714:     <i>10-4.rdf</i> datasource, as do many of those templates. You
  715:     can copy the data out of <a href="#77032">Example 10-4</a> and
  716:     into a file of the same name to use as a datasource.</p>
  717:     <h2><a name="77077"></a> The Mozilla Content Model</h2>
  718:     <p>One theme <!--INDEX content model:overview --> 
  719:     <!--INDEX Gecko rendering engine:Mozilla content model --> of
  720:     this book-and a general goal of the Mozilla development
  721:     environment-is that developers can create real applications
  722:     using many of the same technologies they use to create a web
  723:     page. The Gecko rendering engine, sitting at the heart of
  724:     Mozilla and happily rendering web content, XML files, XUL
  725:     interfaces, and whatever else they can support, is what makes
  726:     this type of development possible. But how does Gecko know what
  727:     to render and how? How can RDF data be handed over so that
  728:     Gecko knows how to draw it?</p>
  729:     <p>When a browser uses the same engine to draw everything-its
  730:     own interface as well as the various kinds of content it
  731:     supports-that engine treats everything as content. Gecko needs
  732:     a way to understand all the various parts of the Mozilla
  733:     browser itself-such as the sidebar, the toolbars, and the mail
  734:     folders and mail messages-as resources it can render and
  735:     display in the Mozilla chrome. This approach to the Mozilla
  736:     application interface is called the content model.</p>
  737:     <p>In Mozilla's content model, XUL documents and other
  738:     interface resources are transformed into RDF when they are
  739:     read. Each chunk of content is represented as a separate RDF
  740:     datasource (see the next section, <a href=
  741:     "#77078">"Datasources</a>," for more information) and is then
  742:     fed to the XUL Content Builder and rendered as the actual bits
  743:     on the screen, as <a href="#77018">Figure 10-9</a> shows.</p>
  744:     <div class="c22">
  745:       <img src="foo.gif">
  746:     </div>
  747:     <p><i>Figure 10-9: <a name="77018"></a></i> <i>Diagram of
  748:     Mozilla's content model</i></p>
  749:     <p>As you can see in <a href="#77018">Figure 10-9</a>, the
  750:     content model can be complex. The XUL documents in <a href=
  751:     "#77018">Figure 10-9</a> are files such as
  752:     <i>navigator.xul</i>, which defines the main browser window's
  753:     basic layout; the RDF documents include files like
  754:     <i>help-toc.rdf</i>, which defines the Mozilla Help viewer's
  755:     table of contents. The list of mail folders and accounts shown
  756:     in <a href="#77034">Example 10-5</a> are part of the built-in
  757:     data that Mozilla renders into browser content.</p>
  758:     <p>Whatever the source, the content model gets everything
  759:     processed in-memory as RDF so that any data can be combined and
  760:     formatted into XUL or other interface code. All sources of RDF
  761:     data are called datasources.</p>
  762:     <h3><a name="77078"></a> Datasources</h3>
  763:     <p>A datasource <!--INDEX content model:datasources --> 
  764:     <!--INDEX datasources:content model --> is a collection of
  765:     related, typically homogenous, RDF statements. A datasource may
  766:     be a single RDF file like <i>localstore.rdf</i>, a combination
  767:     of files, or RDF structures that exist only in memory (as
  768:     discussed later).</p>
  769:     <p>In Mozilla, datasources represent the messages in your email
  770:     inbox, your bookmarks, the packages you installed, your browser
  771:     history, and other sets of data. Datasources can be combined
  772:     easily (or "composed," which is where the term "composite
  773:     datasource" comes from).</p>
  774:     <h4><a name="77079"></a> A datasource example: mailboxes</h4>
  775:     <p>Several <!--INDEX content model:datasources:example --> 
  776:     <!--INDEX datasources:content model:example --> datasources
  777:     describe all the folders and messages in Mozilla's email. A
  778:     root datasource called <tt>msgaccounts</tt> describes which
  779:     mail servers and accounts are present. Separate datasources
  780:     then represent each account separately. These datasources are
  781:     composed to create the entire email storage system. The higher
  782:     levels of this content structure look like <a href=
  783:     "#77034">Example 10-5</a>.</p>
  784:     <p><i>Example 10-5: <a name="77034"></a></i> <i>Content model
  785:     of email datasources</i></p>
  786: <pre>
  787:  msgaccounts:/
  788:  +-- <a href=
  789: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#child&lt;/td&gt; --&gt;
  790:      imap:&lt;/td&gt;<tt><i>//<a href=
  791: "MAILTO:oeschger@imap.netscape.com">oeschger@imap.netscape.com</a></i></tt>
  792:      |    +-- <a href=
  793: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#IsServer&lt;/td&gt; --&gt; "true"
  794:      |    +-- <a href=
  795: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#child&lt;/td&gt; --&gt;
  796:      |        imap:&lt;/td&gt;<tt><i>//<a href=
  797: "MAILTO:oeschger@imap.netscape.com/INBOX">oeschger@imap.netscape.com/INBOX</a></i></tt>
  798:      |    +-- <a href=
  799: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#TotalMessages&lt;/td&gt; --&gt; "4"
  800:      |    +-- <a href=
  801: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#IsServer&lt;/td&gt; --&gt; "false"
  802:      |    +-- <a href=
  803: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#MessageChild&lt;/td&gt; --&gt;
  804:      |        imap_message://<a href=
  805: "MAILTO:oeschger@imap.netscape.com/INBOX">oeschger@imap.netscape.com/INBOX</a>#1
  806:      |    +-- <a href=
  807: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#MessageChild&lt;/td&gt; --&gt;
  808:      |        imap_message://<a href=
  809: "MAILTO:oeschger@imap.netscape.com/INBOX">oeschger@imap.netscape.com/INBOX</a>#2
  810:      |    +-- <a href=
  811: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#MessageChild&lt;/td&gt; --&gt;
  812:      |    etc...
  813:      |
  814:  +-- <a href=
  815: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#child&lt;/td&gt; --&gt;
  816:      mailbox:&lt;/td&gt;<tt><i>//<a href=
  817: "MAILTO:oeschger@pop.netscape.com">oeschger@pop.netscape.com</a></i></tt>
  818:      |    +-- <a href=
  819: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#IsServer&lt;/td&gt; --&gt; "true"
  820:      |    +-- <a href=
  821: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#child&lt;/td&gt; --&gt;
  822:      |        mailbox:&lt;/td&gt;<tt><i>//<a href=
  823: "MAILTO:oeschger@pop.oeschger.com/INBOX">oeschger@pop.oeschger.com/INBOX</a></i></tt>
  824:      |    +-- <a href=
  825: "http://home.netscape.com/NC-rdf">http://home.netscape.com/NC-rdf</a>#TotalMessages&lt;/td&gt; --&gt; "2"
  826:      |    etc...
  827: </pre>
  828:     <p>Each direct child of the root <i>msgaccounts:/</i> is a mail
  829:     server. This portion of the graph shows two Mozilla email
  830:     accounts that are the primary children: <i>imap://<a href=
  831:     "MAILTO:oeschger@imap.netscape.com">oeschger@imap.netscape.com</a></i>
  832:     and <i>mailbox://<a href=
  833:     "MAILTO:oeschger@pop.netscape.com">oeschger@pop.netscape.com</a></i>.
  834:     These two accounts are entirely different datasources that can
  835:     exist on their own. The content model for email actually
  836:     extends much lower than what is represented in this outline. It
  837:     uses RDF to represent the data all the way into the actual
  838:     message lists.</p>
  839:     <h4><a name="77080"></a> Types of datasources</h4>
  840:     <p>As you <!--INDEX content model:datasources:types --> 
  841:     <!--INDEX datasources:content model:types --> may have already
  842:     inferred, email accounts are not actually RDF files. Mozilla
  843:     provides a custom RDF map of all email accounts and messages
  844:     and the content model represents the accounts and their
  845:     relationships to one another as RDF so they can be integrated
  846:     and rendered properly. The interface to this custom mail RDF
  847:     map makes it possible to display a list of messages and
  848:     mailboxes in a <tt>&lt;tree&gt;</tt> template.</p>
  849:     <p>Another example of a datasource, the
  850:     <i>in-memory-datasource,</i> doesn't come from an actual RDF
  851:     file. When an in-memory datasource is created, it doesn't
  852:     contain data. However, data can be inserted into it and stored
  853:     in memory until the datasource is destroyed. In-memory
  854:     datasources frequently represent ephemeral data like search
  855:     results. Other basic datasource types are described in <a href=
  856:     "#77022">Table 10-2</a>.</p>
  857:     <p><i>Table 10-2: <a name="77022"></a></i> <i>Types of
  858:     datasources</i></p>
  859:     <i>all-packages.rdf</i>in the <i>chrome</i>directory, which
  860:     keeps track packages installed in Mozilla) are local
  861:     datasources.<i>assertions</i>, statements that build an
  862:     in-memory data model by adding resources, properties, and value
  863:     to those.<i>filesystem</i>datasource and a
  864:     <i>history</i>datasource.
  865:     <table width="100%" border="1">
  866:       <tr>
  867:         <td><b>Type</b></td>
  868:         <td><b>Description</b></td>
  869:       </tr>
  870:       <tr>
  871:         <td>Local datasource</td>
  872:         <td>A local datasource is an RDF graph contained in an
  873:         RDF/XML file on a local disk. All RDF files in the chrome
  874:         registry (e.g.,</td>
  875:       </tr>
  876:       <tr>
  877:         <td>Remote datasource</td>
  878:         <td>RDF can be accessed locally or remotely. A remote
  879:         datasource is an RDF/XML file stored on a server and
  880:         accessed with a URL.</td>
  881:       </tr>
  882:       <tr>
  883:         <td>In-memory datasource</td>
  884:         <td>An in-memory datasource exists only in memory during a
  885:         Mozilla session. In-memory datasources are built with</td>
  886:       </tr>
  887:       <tr>
  888:         <td>Built-in datasource</td>
  889:         <td>These unique, prefabricated datasources represent
  890:         something used often in Mozilla, such as a built-in</td>
  891:       </tr>
  892:       <tr>
  893:         <td>Composite datasource</td>
  894:         <td>A composite datasource may be a combination of any of
  895:         the datasources previously listed. RDF allows you to merge
  896:         different graphs.</td>
  897:       </tr>
  898:     </table>
  899:     <h2><a name="77081"></a> RDF Components and Interfaces</h2>
  900:     <p>Once you are comfortable using XUL templates to display RDF
  901:     data (see <a href="ch09.html#77034">Chapter 9</a>), you should
  902:     explore the various ways to create and change that data. In
  903:     Mozilla, data is generally RDF, since all data in Mozilla is
  904:     either represented formally in RDF or passed through the
  905:     RDF-based content model for display. Use the tools described in
  906:     this section to manipulate RDF and the data it represents.</p>
  907:     <p>Mozilla has a great set of interfaces for creating,
  908:     manipulating, and managing RDF, and it also provides ready-made
  909:     RDF components that represent datasources used in Mozilla.
  910:     Think of RDF interfaces as ways to manipulate RDF directly and
  911:     of RDF components as sets of the interfaces already associated
  912:     with a particular kind of data, such as bookmarks. Interfaces
  913:     tend to deal with the RDF model itself, without regard to the
  914:     kinds of data being handled, while RDF components give you
  915:     control over specific Mozilla data. See the next two sections
  916:     for more information on RDF interfaces and components.</p>
  917:     <h3><a name="77082"></a> What Is an RDF Component?</h3>
  918:     <p>An RDF 
  919:     <!--INDEX RDF (Resource Description Framework):components, overview -->
  920:     <!--INDEX components:RDF, overview --> component may implement
  921:     any number of the general RDF interfaces described here, in
  922:     addition to special interfaces for accessing and controlling
  923:     the data the datasource represents. For example,
  924:     <tt>@mozilla.org/rdf/data-source;1?name=internetsearch</tt> is
  925:     an RDF component used to control Mozilla's internet searching
  926:     facility. In Mozilla, a component can act as a library of code
  927:     specific to a given set of data or domain. The <tt>
  928:     <!--INDEX internetsearch component --> internetsearch</tt>
  929:     component is instantiated and used to recall text entered in a
  930:     previous search:</p>
  931: <pre>
  932: var searchDS = Components.classes["@mozilla.org/rdf/datasource;1?name=internetsearch"]
  933: .getService(Components.interfaces.nsIInternetSearchService);
  934: searchDS.RememberLastSearchText(escapedSearchStr);
  935: </pre>
  936:     <p>This RDF component implements an interface called <i>
  937:     <!--INDEX nsIInternetSearchService interface --> 
  938:     <!--INDEX interfaces:nsIInternetSearchService -->
  939:     nsIInternetSearchService</i>, which is selected from the
  940:     component and used to call the <tt>RememberLastSearchText</tt>
  941:     method. Although you can also use the <tt>getService</tt>
  942:     method to get one of a component's RDF interfaces (e.g., by
  943:     using
  944:     <tt>getService(Components.interfaces.nsIRDFDataSource)</tt>),
  945:     doing so is seldom necessary in practice. RDF components are
  946:     tailored to the datasources they represent and usually provide
  947:     all the access you need to access that data directly. <a href=
  948:     "#77036">Example 10-6</a> lists RDF components in Mozilla.</p>
  949:     <p><i>Example 10-6: <a name="77036"></a></i> <i>RDF-specific
  950:     components built into Mozilla</i></p>
  951: <pre>
  952:  @mozilla.org/rdf/container;1
  953:  @mozilla.org/rdf/content-sink;1
  954:  @mozilla.org/rdf/datasource;1?name=addresscard
  955:  @mozilla.org/rdf/datasource;1?name=addressdirectory
  956:  @mozilla.org/rdf/datasource;1?name=bookmarks
  957:  @mozilla.org/rdf/datasource;1?name=charset-menu
  958:  @mozilla.org/rdf/datasource;1?name=composite-datasource
  959:  @mozilla.org/rdf/datasource;1?name=files
  960:  @mozilla.org/rdf/datasource;1?name=history
  961:  @mozilla.org/rdf/datasource;1?name=httpindex
  962:  @mozilla.org/rdf/datasource;1?name=in-memory-datasource
  963:  @mozilla.org/rdf/datasource;1?name=internetsearch
  964:  @mozilla.org/rdf/datasource;1?name=ispdefaults
  965:  @mozilla.org/rdf/datasource;1?name=local-store
  966:  @mozilla.org/rdf/datasource;1?name=localsearch
  967:  @mozilla.org/rdf/datasource;1?name=mailnewsfolders
  968:  @mozilla.org/rdf/datasource;1?name=msgaccountmanager
  969:  @mozilla.org/rdf/datasource;1?name=msgfilters
  970:  @mozilla.org/rdf/datasource;1?name=msgnotifications
  971:  @mozilla.org/rdf/datasource;1?name=smtp
  972:  @mozilla.org/rdf/datasource;1?name=subscribe
  973:  @mozilla.org/rdf/datasource;1?name=window-mediator
  974:  @mozilla.org/rdf/datasource;1?name=xml-datasource
  975:  @mozilla.org/rdf/delegate-factory;1?key=filter&amp;scheme=imap
  976:  @mozilla.org/rdf/delegate-factory;1?key=filter&amp;scheme=mailbox
  977:  @mozilla.org/rdf/delegate-factory;1?key=filter&amp;scheme=news
  978:  @mozilla.org/rdf/delegate-factory;1?key=smtpserver&amp;scheme=smtp
  979:  @mozilla.org/rdf/rdf-service;1
  980:  @mozilla.org/rdf/resource-factory;1
  981:  @mozilla.org/rdf/resource-factory;1?name=abdirectory
  982:  @mozilla.org/rdf/resource-factory;1?name=abmdbcard
  983:  @mozilla.org/rdf/resource-factory;1?name=abmdbdirectory
  984:  @mozilla.org/rdf/resource-factory;1?name=imap
  985:  @mozilla.org/rdf/resource-factory;1?name=mailbox
  986:  @mozilla.org/rdf/resource-factory;1?name=news
  987:  @mozilla.org/rdf/xml-parser;1
  988:  @mozilla.org/rdf/xml-serializer;1
  989: </pre>
  990:     <p>From this list, components used often in the Mozilla source
  991:     code include bookmarks, history, mail and news folders, and
  992:     address books.</p>
  993:     <blockquote>
  994:       <hr>
  995:       <b>Special URIs</b> 
  996:       <p>Mozilla's built-in datasource 
  997:       <!--INDEX URIs (Universal Resource Identifiers):datasource components -->
  998:       <!--INDEX components:URIs --> components have special URIs
  999:       for access. Here is the format used to determine the URI from
 1000:       the component reference:</p>
 1001:       <p>Component:</p>
 1002: <pre>
 1003: @mozilla.org/rdf/datasource;1?name=SomeName
 1004: </pre>
 1005:       Datasource URI: 
 1006: <pre>
 1007: rdf:SomeName
 1008: </pre>
 1009:       The URI is also accessible as a datasource property:
 1010:       <hr>
 1011:     </blockquote>
 1012:     foo-ds.URI 
 1013:     <h3><a name="77083"></a> What Are RDF Interfaces?</h3>
 1014:     <p>RDF interfaces 
 1015:     <!--INDEX RDF (Resource Description Framework):interfaces:overview -->
 1016:     <!--INDEX interfaces:RDF:overview --> are interfaces in Mozilla
 1017:     designed to manipulate RDF structures and data. They typically
 1018:     deal with RDF generally, rather than specific sets of data (as
 1019:     in the case of components). A common use for an RDF interface
 1020:     in JavaScript, shown in <a href="#77038">Example 10-7</a>, is
 1021:     to use <i>nsIRDFService</i> to retrieve or assert the root node
 1022:     of an RDF datasource.</p>
 1023:     <p><i>Example 10-7: <a name="77038"></a></i> <i>Creating a root
 1024:     node</i></p>
 1025: <pre>
 1026:  // get the nsIRDFService interface and assign it to RDF
 1027:  RDF = Components.classes&lt;/td&gt;<a href=
 1028: "MAILTO:[`@mozilla.org/rdf/rdf-service;1">[`@mozilla.org/rdf/rdf-service;1</a>'].
 1029:        getService(Components.interfaces.nsIRDFService);
 1030:  // call the GetResource method from the interface
 1031:  rootResource = RDF.GetResource('urn:root');
 1032: </pre>
 1033:     <p>Like all Mozilla interfaces, RDF interfaces (shown in <a
 1034:     href="#77024">Table 10-3</a>) are defined in IDL and can be
 1035:     accessed through XPCOM. The examples in this section use
 1036:     JavaScript and XPConnect to access the components for
 1037:     simplicity, but you can also use these interfaces with C++, as
 1038:     they are often in the actual Mozilla source code. Most
 1039:     interfaces deal with datasources, which drive the use of RDF in
 1040:     Mozilla.</p>
 1041:     <p><i>Table 10-3: <a name="77024"></a></i> <i>Mozilla's
 1042:     built-in RDF interfaces</i></p>
 1043:     <tt>nsIRDFService</tt>.
 1044:     <table width="100%" border="1">
 1045:       <tr>
 1046:         <td><b>RDF interface</b></td>
 1047:         <td><b>Description</b></td>
 1048:       </tr>
 1049:       <tr>
 1050:         <td>nsIRDFService</td>
 1051:         
 1052:     <td>Mostly used for retrieving datasources, resources, and literals. It also 
 1053:       registers and unregisters datasources and resources.</td>
 1054:       </tr>
 1055:       <tr>
 1056:         <td>nsIRDFCompositeDataSource</td>
 1057:         <td>Allows the addition and removal of a datasource from a
 1058:         composite datasource (which may be empty).</td>
 1059:       </tr>
 1060:       <tr>
 1061:         <td>nsIRDFDataSource, nsIRDFPurgeableDataSource,
 1062:         nsIRDFRemoteDataSource</td>
 1063:         <td>Mostly used for adding, removing, and changing triples
 1064:         in a datasource. It provides the means to change the
 1065:         graph.</td>
 1066:       </tr>
 1067:       <tr>
 1068:         <td>nsIRDFNode, nsIRDFResource, nsIRDFLiteral</td>
 1069:         <td>Provide an equality function. Values for resources and
 1070:         literals can be retrieved. Objects of these types are
 1071:         retrieved from</td>
 1072:       </tr>
 1073:       <tr>
 1074:         <td>nsIRDFContainer</td>
 1075:         <td>Provides vector-like access to an RDF container's
 1076:         elements.</td>
 1077:       </tr>
 1078:       <tr>
 1079:         <td>nsIRDFContainerUtils</td>
 1080:         <td>Provides container creation and other container-related
 1081:         functions.</td>
 1082:       </tr>
 1083:       <tr>
 1084:         <td>nsIRDFObserver</td>
 1085:         <td>Fires events when data is changed in a datasource.</td>
 1086:       </tr>
 1087:       <tr>
 1088:         <td>nsIRDFXMLParser, nsIRDFXMLSerializer, nsIRDFXMLSink,
 1089:         nsIRDFXMLSource</td>
 1090:         <td>Used for working with RDF/XML. Functions are provided
 1091:         for parsing files and serializing content.</td>
 1092:       </tr>
 1093:     </table>
 1094:     <p>The sheer variety of RDF interfaces may seem overwhelming,
 1095:     but all interfaces serve different purposes and are often used
 1096:     in conjunction with one another. In your particular application
 1097:     space, you may find yourself using some subsets of these
 1098:     interfaces constantly and others not at all. This section
 1099:     describes some of the most commonly used functions. You can
 1100:     look up all of interfaces in their entirety 
 1101:     <!--INDEX web sites:RDF interfaces --> at <i><a href=
 1102:     "http://lxr.mozilla.org/seamonkey/source/rdf/base/idl/">http://lxr.mozilla.org/seamonkey/source/rdf/base/idl/</a></i>.</p>
 1103:     <h3><a name="77084"></a> nsIRDFService</h3>
 1104:     <p>If you <!--INDEX nsIRDFService interface --> 
 1105:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFService -->
 1106:     <!--INDEX interfaces:RDF:nsIRDFService --> will do any sort of
 1107:     RDF processing, you need to use the <i>nsIRDFService</i>
 1108:     interface. It provides the basics for working with datasources,
 1109:     resources, and literals, and is useful when you process RDF
 1110:     data. <i>nsIRDFService</i> can be initialized by using the
 1111:     <tt>getService</tt> method of the <tt>rdf-service</tt>
 1112:     class:</p>
 1113: <pre>
 1114: RDF = Components.<a href=
 1115: "MAILTO:classes[`@mozilla.org/rdf/rdf-service;1">classes[`@mozilla.org/rdf/rdf-service;1</a>']
 1116: getService(Components.interfaces.nsIRDFService);
 1117: </pre>
 1118:     <p>Once the service is available, it's ready to go to work.
 1119:     Even though no datasource is created yet (in this particular
 1120:     example), the RDF service can still get resources and literals,
 1121:     as shown in the next section.</p>
 1122:     <h4><a name="77085"></a> Getting a resource</h4>
 1123:     <p>Once a resource 
 1124:     <!--INDEX resources:nsIRDFService interface --> is created
 1125:     (e.g., with the identifier <tt>urn:root</tt> in <a href=
 1126:     "#77038">Example 10-7</a>), it needs to be added to a
 1127:     datasource:</p>
 1128: <pre>
 1129: rootResource = RDF.GetResource('urn:root');
 1130: </pre>
 1131:     <p>When a resource is already registered under the given
 1132:     identifier (see <a href="#77088">"Registering and unregistering
 1133:     datasources</a>," later in this chapter for more information
 1134:     about RDF registration), then <tt>
 1135:     <!--INDEX GetResource function --> GetResource</tt> returns
 1136:     that resource.</p>
 1137:     <h4><a name="77086"></a> Getting an anonymous resource</h4>
 1138:     <p>Anonymous resources are resources with no resource
 1139:     identifier. Here is the creation of a new anonymous resource
 1140:     and a test of its anonymity:</p>
 1141: <pre>
 1142: anonResource = RDF.GetAnonymousResource( );
 1143: // This would be true. Checking is not necessary, just here for example.
 1144: isAnon = RDF.isAnonymousResource(anonResource);
 1145: </pre>
 1146:     <p>Typically, these resources are turned into containers, as
 1147:     shown in the next section. Anonymous resources exist when names
 1148:     are not needed and a simple reference to that resource is all
 1149:     that is required.</p>
 1150:     <h4><a name="77087"></a> Getting a literal</h4>
 1151:     <p>The <tt><!--INDEX GetLiteral function --> GetLiteral</tt>
 1152:     function <!--INDEX literals:nsIRDFService interface --> returns
 1153:     the given name in the format of a literal, which you can then
 1154:     use to assert into an RDF graph as a resource.</p>
 1155: <pre>
 1156: myName = RDF.GetLiteral('Eric');
 1157: </pre>
 1158:     <p>Variations on this function are <tt>GetIntLiteral</tt> and
 1159:     <tt>GetDateLiteral</tt>.</p>
 1160:     <h4><a name="77088"></a> Registering and unregistering
 1161:     datasources</h4>
 1162:     <p>If you create <!--INDEX datasources:registering --> 
 1163:     <!--INDEX registering:datasources --> 
 1164:     <!--INDEX RDF (Resource Description 
 1165:     Framework):datasources, registering --> a Mozilla application
 1166:     that uses the same datasource or RDF resources in different
 1167:     ways, you may want to register the datasource with Mozilla.
 1168:     When you register a datasource, you register it as a component
 1169:     in Mozilla (see <a href="ch08.html#77062">"Component Manager"
 1170:     in Chapter 8</a> for more information on Mozilla's component
 1171:     model), which means it can be accessed and used as easily as
 1172:     any other XPCOM component, and from anywhere in Mozilla.</p>
 1173:     <p>To register a datasource, call the <tt>
 1174:     <!--INDEX RegisterDatasource method --> RegisterDatasource</tt>
 1175:     method of the RDF Service. In this example, the datasource
 1176:     already exists and is assigned to a variable named
 1177:     <i>myDatasource</i>:</p>
 1178: <pre>
 1179: RDF.RegisterDataSource(myDatasource, false);
 1180: </pre>
 1181:     <p>In this case, <i>myDatasource</i> is the datasource name,
 1182:     and the <tt>false</tt> parameter specifies that this datasource
 1183:     is not replacing a datasource with the same name. Once a
 1184:     datasource is registered with the component manager in this
 1185:     way, it can be retrieved by name and associated with another
 1186:     instance:</p>
 1187: <pre>
 1188: secondDatasource = anotherRDF.GetDataSource("My Datasource");
 1189: </pre>
 1190:     <p>To unregister a datasource from the RDF Service, pass the
 1191:     datasource into the <tt>UnRegisterDataSource</tt> function:</p>
 1192: <pre>
 1193: RDF.UnRegisterDataSource(myDatasource);
 1194: </pre>
 1195:     <p>Once it's unregistered, a datasource is no longer available
 1196:     to other instances of the RDF Service. Registered resources
 1197:     work the same way as datasources in the RDF Service: if a
 1198:     resource is registered with the RDF Service, then it is
 1199:     available in every instance of RDF Service. To get two
 1200:     different instances of the same registered datasource and
 1201:     unregister its use:</p>
 1202: <pre>
 1203: newResource = RDF.GetResource('my.resource');
 1204: RDF.RegisterResource(newResource,false);
 1205: notNewResource = RDF.GetResource('my.resource');
 1206: RDF.UnRegisterResource(notNewResource);
 1207: </pre>
 1208:     <blockquote>
 1209:       <div class="c21">
 1210:         NOTE
 1211:       </div>
 1212:       <p>If you register resources and datasources, be sure to use
 1213:       the <i>overwrite</i> Boolean variable on
 1214:       <tt>RegisterDataSource</tt> and <tt>RegisterResource</tt> to
 1215:       avoid overwriting existing datasources.</p>
 1216:     </blockquote>
 1217:     <h4><a name="77089"></a> Getting a remote datasource</h4>
 1218:     <p>Finally, <i>nsIRDFService</i> provides 
 1219:     <!--INDEX datasources:remote, getting --> 
 1220:     <!--INDEX remote datasources, getting --> a useful method that
 1221:     loads a datasource from a remote server, which is a process
 1222:     that occurs asynchronously. Compared to forthcoming discussions
 1223:     about datasource loading, <tt>GetDataSource</tt> is a real
 1224:     shortcut:</p>
 1225: <pre>
 1226: remoteDatasource = RDF.GetDataSource('<a href=
 1227: "http://books.mozdev.org/file.rdf">http://books.mozdev.org/file.rdf</a>');
 1228: </pre>
 1229:     <blockquote>
 1230:       <div class="c21">
 1231:         NOTE
 1232:       </div>
 1233:       <p>Remember that RDF files requested in this way must be set
 1234:       with the text/rdf MIME type on the web server to load
 1235:       properly.</p>
 1236:     </blockquote>
 1237:     <h3><a name="77090"></a> nsIRDFCompositeDataSource</h3>
 1238:     <p>When you work 
 1239:     <!--INDEX nsIRDFCompositeDataSource interface --> 
 1240:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFCompositeDataSource -->
 1241:     <!--INDEX interfaces:RDF:nsIRDFCompositeDataSource --> with
 1242:     multiple datasources, you can make things easier by grouping
 1243:     them, which <i>nsIRDFCompositeDataSource</i> allows you to do.
 1244:     This functionality aggregates data in a number of Mozilla's
 1245:     applications. To get this interface, invoke:</p>
 1246: <pre>
 1247: composite_datasource
 1248: = '@mozilla.org/rdf/datasource;1?name=composite-datasource';
 1249: compDataSource = Components.classes[composite_datasource]
 1250: getService(Components.interfaces.nsIRDFCompositeDataSource);
 1251: </pre>
 1252:     <p>Once you have the interface, adding and removing datasources
 1253:     from the composite is easy. You can also enumerate the
 1254:     datasources by using the <tt>getNext</tt> method. <a href=
 1255:     "#77040">Example 10-8</a> demonstrates how to add, remove, and
 1256:     cycle through datasources.</p>
 1257:     <p><i>Example 10-8: <a name="77040"></a></i> <i>Manipulating
 1258:     datasources</i></p>
 1259: <pre>
 1260:  compDataSource.AddDataSource(datasource1);
 1261:  compDataSource.AddDataSource(datasource2);
 1262:  compDataSource.AddDataSource(datasource3);
 1263:  compDataSource.RemoveDataSource(datasource1);
 1264:  allDataSources = compDataSource.GetDataSources( );
 1265:  datasource2 = allDataSources.getNext( );
 1266:  datasource2.QueryInterface(Components.interfaces.nsIRDFDataSource);
 1267:  datasource3 = allDataSources.getNext( );
 1268:  datasource3.QueryInterface(Components.interfaces.nsIRDFDataSource);
 1269: </pre>
 1270:     <p>In <a href="#77040">Example 10-8</a>,
 1271:     <tt>allDataSources</tt> is an <i>nsISimpleEnumerator</i>
 1272:     returned by the <tt>GetDataSources</tt> method on the composite
 1273:     datasource. <tt>datasource1</tt> is removed from the composite,
 1274:     and then the remaining datasources are cycled through. This
 1275:     step provides a way to iterate through a collection of
 1276:     datasources. <i>nsIRDFCompositeDatasource</i> also inherits the
 1277:     many functions of <i>nsIRDFDataSource</i>; refer to the section
 1278:     <a href="#77091">"nsIRDFDataSource</a>" for more
 1279:     information.</p>
 1280:     <h3><a name="77091"></a> nsIRDFDataSource</h3>
 1281:     <p>The <i><!--INDEX nsIRDFDataSource interface --> 
 1282:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFDataSource -->
 1283:     <!--INDEX interfaces:RDF:nsIRDFDataSource -->
 1284:     nsIRDFDataSource</i> interface is large, with twenty functions
 1285:     and one attribute (<tt>URI</tt>), so it's one of the most
 1286:     common interfaces used to manipulate RDF data.
 1287:     <i>nsIRDFDataSource</i> contains all the components in <a href=
 1288:     "#77036">Example 10-6</a> with "datasource" in their contract
 1289:     IDs, along with other common components:</p>
 1290: <pre>
 1291: @mozilla.org/browser/bookmarks-service;1
 1292: @mozilla.org/related-links-handler;1
 1293: @mozilla.org/browser/localsearch-service;1
 1294: @mozilla.org/registry-viewer;1
 1295: @mozilla.org/browser/global-history;1
 1296: </pre>
 1297:     <p>The <i>nsIRDFDataSource</i> interface is meant to handle
 1298:     some of the core interaction with the datasource. APIs such as
 1299:     <tt>URI</tt>, <tt>GetTarget</tt>, <tt>Assert</tt>, and
 1300:     <tt>Change</tt> are helpful for working on the RDF graph
 1301:     itself. For example, the
 1302:     <tt>@mozilla.org/rdf/datasource;1?name=in-memory-datasource</tt>
 1303:     RDF component demonstrates the use of the
 1304:     <i>nsIRDFDataSource</i> interface. When this component is
 1305:     created, it's a blank datasource in memory, into which objects
 1306:     are inserted, changed, and removed. You can access the
 1307:     <i>nsIRDFDataSource</i> interface from the RDF component by
 1308:     first constructing an RDF graph in the in-memory
 1309:     datasource:</p>
 1310: <pre>
 1311: mem = '@mozilla.org/rdf/datasource;1?name=in-memory-datasource';
 1312: datasource = Components.classes[mem].
 1313: createInstance(Components.interfaces.nsIRDFDataSource);
 1314: </pre>
 1315:     <p>Of the twenty functions (found at <i><a href=
 1316:     "http://lxr.mozilla.org/seamonkey/source/rdf/base/idl/nsIRDFDataSource.idl">
 1317:     http://lxr.mozilla.org/seamonkey/source/rdf/base/idl/nsIRDFDataSource.idl</a></i>)
 1318:     in this interface, we show only a handful here:</p>
 1319:     <ul>
 1320:       <li>Assertion and removal</li>
 1321:       <li>Changing values</li>
 1322:       <li>Moving triples</li>
 1323:       <li>HasAssertion</li>
 1324:       <li>GetTarget</li>
 1325:       <li>GetSource</li>
 1326:     </ul>
 1327:     <p>The main purpose of the <i>nsIRDFDatasource</i> interface is
 1328:     to work with RDF triples inside a datasource, allowing you to
 1329:     change that datasource's RDF graph.</p>
 1330:     <h4><a name="77092"></a> Assertion and removal</h4>
 1331:     <p>Recall from the 
 1332:     <!--INDEX triples:nsIRDFDataSource interface --> <a href=
 1333:     "#77065">"RDF triples: subject, predicate, and object</a>"
 1334:     section, earlier in this chapter, that triples are RDF
 1335:     statements in which the relationship between the subject,
 1336:     predicate, and object is more strictly defined. In the
 1337:     interface code, a triple's elements are all typically defined
 1338:     as resources rather than plain URIs, which means they can be
 1339:     asserted into a datasource in the particular sequence that
 1340:     makes them meaningful as parts of a triple:</p>
 1341: <pre>
 1342: rootSubject = RDF.GetResource('urn:root');
 1343: predicate = RDF.GetResource('<a href=
 1344: "http://books.mozdev.org/rdf">http://books.mozdev.org/rdf</a>#chapters');
 1345: object = RDF.GetResource('Chapter1');
 1346: datasource.Assert(rootSubject,predicate,object,true);
 1347: </pre>
 1348:     <p>Once you assert the statement's elements into the datasource
 1349:     in this way, the datasource contains the triple. The
 1350:     <tt>truth</tt> value parameter in the last slot indicates that
 1351:     the given node is "locked" and thus cannot be overwritten.</p>
 1352:     <p>Removing a triple from the datasource is as easy as adding
 1353:     it. If you try to remove a triple that doesn't exist, your
 1354:     request is ignored and no error messages are raised. To
 1355:     unassert a triple in the datasource, use:</p>
 1356: <pre>
 1357: rootSubject = RDF.GetResource('urn:root');
 1358: predicate = RDF.GetResource('<a href=
 1359: "http://books.mozdev.org/rdf">http://books.mozdev.org/rdf</a>#chapters');
 1360: object = RDF.GetResource('Chapter8');
 1361: datasource.Unassert(rootSubject,predicate,object);
 1362: </pre>
 1363:     <h4><a name="77093"></a> Changing values</h4>
 1364:     <p>Changing values <!--INDEX literals:values, changing --> 
 1365:     <!--INDEX datasources:values, changing --> in a datasource is
 1366:     also very easy. Assert and change a literal in the datasource
 1367:     as follows:</p>
 1368: <pre>
 1369: subject = RDF.GetResource('Chapter1');
 1370: predicate = RDF.GetResource('<a href=
 1371: "http://books.mozdev.org/rdf">http://books.mozdev.org/rdf</a>#title');
 1372: object = RDF.GetLiteral('Mozilla as a Platform');
 1373: datasource.Assert(subject,predicate,object,true);
 1374: newObject = RDF.GetLiteral('Mozilla is a cool Platform!');
 1375: datasource.Change(subject,predicate,newObject,);
 1376: </pre>
 1377:     <p>If working with triples seems hard in the template
 1378:     generation, their use in these examples-where adding to and
 1379:     changing the parts is so easy-may make things clearer.</p>
 1380:     <h4><a name="77094"></a> Moving triples</h4>
 1381:     <p>Moving a triple <!--INDEX triples:moving --> in a datasource
 1382:     also requires some simple code. This example moves the asserted
 1383:     triple in the previous section:</p>
 1384: <pre>
 1385: newSubject = RDF.GetResource('Chapter99');
 1386: // Moving from Chapter1 to Chapter99
 1387: datasource.Move(subject,newSubject,predicate,object);
 1388: </pre>
 1389:     <h4><a name="77095"></a> HasAssertion</h4>
 1390:     <p>This next example <!--INDEX HasAssertion function --> checks
 1391:     if the previous statement still exists in the datasource.</p>
 1392: <pre>
 1393: datasource.HasAssertion(newSubject,predicate,object,true);
 1394: </pre>
 1395:     <p>This function is useful when you create new statements and
 1396:     resources and want to make sure you are not overwriting
 1397:     pre-existing resources.</p>
 1398:     <h4><a name="77096"></a> GetTarget</h4>
 1399:     <p>The <tt><!--INDEX GetTarget method --> GetTarget</tt> method
 1400:     returns the resource's property value (i.e., the object). Given
 1401:     the RDF statement "(Eric) wrote (a book)," for example, the
 1402:     <tt>GetTarget</tt> method would input "Eric" and "wrote" and
 1403:     get back the object "a book." Once again, the example code is
 1404:     based on the previous examples:</p>
 1405: <pre>
 1406: object = datasource.GetTarget(newSubject,predicate,true);
 1407: objects = datasource.GetTargets(rootSubject,predicate,true);
 1408: // objects is an nsIEnumeration of the object and its properties
 1409: </pre>
 1410:     <p>In addition to <tt>GetTarget</tt>, as seen above, a
 1411:     <tt>GetTargets</tt> function returns an object and its
 1412:     properties in an enumeration. This function can be very handy
 1413:     for quick access to resources with fewer function calls.</p>
 1414:     <h4><a name="77097"></a> GetSource</h4>
 1415:     <p><tt><!--INDEX GetSource method --> GetSource</tt> is the
 1416:     inverse of <tt>GetTarget</tt>. Whereas <tt>GetTarget</tt>
 1417:     returns an object, <tt>GetSource</tt> returns the subject
 1418:     attached to an object. Given the RDF statement "(Eric) wrote (a
 1419:     book)" again, in other words, the <tt>GetSource</tt> method
 1420:     would input "wrote" and "a book" and get back the statement
 1421:     subject "Eric."</p>
 1422: <pre>
 1423: subject = datasource.GetSource(object,predicate,true);
 1424: subjects = datasource.GetSources(object,predicate,true);
 1425: // subjects is an nsIEnumeration of the subject and its properties
 1426: </pre>
 1427:     <p>When you create RDF statements with assertions or work with
 1428:     in-memory datasources, it is often difficult to remember the
 1429:     shape of the graph, which statements exist about which
 1430:     resources, or which objects are attached to which subjects.
 1431:     These "getter" methods can help you verify the shape of your
 1432:     graph.</p>
 1433:     <h3><a name="77098"></a> nsIRDFRemoteDataSource</h3>
 1434:     <p>The <!--INDEX nsIRDFRemoteDataSource interface --> 
 1435:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFRemoteDataSource -->
 1436:     <!--INDEX interfaces:RDF:nsIRDFRemoteDataSource --> <a href=
 1437:     "#77084">"nsIRDFService</a>" section (earlier in this chapter)
 1438:     showed how to load a datasource from a remote server simply. If
 1439:     you want control over that datasource, you can manage it by
 1440:     using the <i>nsIRDFRemoteDatasource</i> to set up a remote
 1441:     datasource:</p>
 1442: <pre>
 1443: xml = '@mozilla.org/rdf/datasource;1?name=xml-datasource';
 1444: datasource = Components.classes[xml].
 1445: createInstance(Components.interfaces.nsIRDFRemoteDataSource);
 1446: datasource.Init('<a href=
 1447: "http://books.mozdev.org/file.rdf">http://books.mozdev.org/file.rdf</a>');
 1448: datasource.Refresh(false);
 1449: </pre>
 1450:     <p>In this example, the <tt>Init</tt> and <tt>Refresh</tt>
 1451:     methods control the datasource on the server. In addition to
 1452:     these methods, you can call the <tt>Flush</tt> method to flush
 1453:     the data that's been changed and reload, or you can check
 1454:     whether the datasource is loaded by using the <tt>loaded</tt>
 1455:     property:</p>
 1456: <pre>
 1457: if (datasource.loaded) {
 1458: // Do something
 1459: }
 1460: </pre>
 1461:     <p>Built-in datasources that implement
 1462:     <i>nsIRDFRemoteDataSource</i> (and other necessary interfaces)
 1463:     and do their own data handling include:</p>
 1464: <pre>
 1465: @mozilla.org/rdf/datasource;1?name=history
 1466: @mozilla.org/browser/bookmarks-service;1
 1467: @mozilla.org/autocompleteSession;1?type=history
 1468: @mozilla.org/browser/global-history;1
 1469: @mozilla.org/rdf/datasource;1?name=bookmarks
 1470: </pre>
 1471:     <h3><a name="77099"></a> nsIRDFPurgeableDataSource</h3>
 1472:     <p>Using <!--INDEX nsIRDFPurgeableDataSource interface --> 
 1473:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFPurgeableDataSource -->
 1474:     <!--INDEX interfaces:RDF:nsIRDFPurgeableDataSource --> the
 1475:     <i>nsIRDFPurgeableDatasource</i> interface allows you to delete
 1476:     a whole section of an existing in-memory datasource in one fell
 1477:     swoop. This means that all relatives-all statements derived
 1478:     from that node-are removed. When you work with large in-memory
 1479:     datasources (such as email systems), the using interface can
 1480:     manipulate the data efficiently. The <tt>Sweep( )</tt> method
 1481:     can delete a section that is marked in the datasource.</p>
 1482: <pre>
 1483: datasource.
 1484: QueryInterface(Components.interfaces.nsIRDFPurgeableDataSource);
 1485: rootSubject = RDF.GetResource('urn:root');
 1486: predicate = RDF.GetResource('<a href=
 1487: "http://books.mozdev.org/rdf">http://books.mozdev.org/rdf</a>#chapters');
 1488: object = RDF.GetResource('Chapter1');
 1489: datasource.Mark(rootSubject,predicate,object,true);
 1490: datasource.Sweep( );
 1491: </pre>
 1492:     <p>In this instance, a statement about a chapter in a book is
 1493:     marked and then removed from the datasource. You can also mark
 1494:     more than one node before sweeping.</p>
 1495:     <h3><a name="77100"></a> nsIRDFNode, nsIRDFResource, and
 1496:     nsIRDFLiteral</h3>
 1497:     <p>These types of objects come from only a few different
 1498:     places. Here are all the functions that can return the resource
 1499:     of a literal:</p>
 1500: <pre>
 1501: nsIRDFService.GetResource
 1502: nsIRDFService.GetAnonymousResource
 1503: nsIRDFService.GetLiteral
 1504: nsIRDFDataSource.GetSource
 1505: nsIRDFDataSource.GetTarget
 1506: </pre>
 1507:     <p><i>nsIRDFNode <!--INDEX nsIRDFNode interface --> 
 1508:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFNode -->
 1509:     <!--INDEX interfaces:RDF:nsIRDFNode --></i> is the parent of
 1510:     <i>nsIRDFResource</i> and <i>nsIRDFLiteral</i>. It is not used
 1511:     often because it's sole function is to test equality:</p>
 1512: <pre>
 1513: isEqual = resource1.EqualsNode(resource2);
 1514: </pre>
 1515:     <p>The other two interfaces inherit this function
 1516:     automatically. <tt>EqualsNode</tt> tests the equivalency of two
 1517:     resources, which can be useful when you try to put together
 1518:     different statements (e.g., "Eric wrote a book" and "[This]
 1519:     book is about XML") and want to verify that a resource like
 1520:     "book" is the same in both cases.</p>
 1521:     <h4><a name="77101"></a> nsIRDFResource</h4>
 1522:     <p>Like <!--INDEX nsIRDFResource interface --> 
 1523:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFResource -->
 1524:     <!--INDEX interfaces:RDF:nsIRDFResource --> <i>nsIRDFNode</i>,
 1525:     <i>nsIRDFResource</i> is a minimalist interface. Here are the
 1526:     functions and the property available in a resource from the
 1527:     <i>nsIRDFResource</i> interface:</p>
 1528: <pre>
 1529: resource = RDF.GetAnonymousResource( );
 1530: // get the resource value, something like 'rdf:#$44RG7'
 1531: resourceIdentifierString = resource.Value;
 1532: // compare the resource to an identifier
 1533: isTrue = resourceEqualsString(resourceIdentifierString);
 1534: // Give the resource a real name.
 1535: resource.Init('Eric');
 1536: </pre>
 1537:     <h4><a name="77102"></a> nsIRDFLiteral</h4>
 1538:     <p>A literal's <!--INDEX nsIRDFLiteral interface --> 
 1539:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFLiteral -->
 1540:     <!--INDEX interfaces:RDF:nsIRDFLiteral --> value can be read
 1541:     but not written. To change the value of a literal, make a new
 1542:     literal and set it properly:</p>
 1543: <pre>
 1544: aValue = literal.Value;
 1545: </pre>
 1546:     <p>Note that <tt>aValue</tt> could be a string or an integer in
 1547:     this case. The base type conversion, based on the data's
 1548:     format, is done automatically.</p>
 1549:     <h3><a name="77103"></a> nsIRDFContainerUtils</h3>
 1550:     <p>This interface <!--INDEX nsIRDFContainerUtils interface --> 
 1551:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFContainerUtils -->
 1552:     <!--INDEX interfaces:RDF:nsIRDFContainerUtils --> facilitates
 1553:     the creation of containers and provides other container-related
 1554:     functions. It provides functions that make and work with a
 1555:     <tt>sequence</tt>, <tt>bag</tt>, and <tt>alternative</tt>. (The
 1556:     functions work the same way for all types of containers, so
 1557:     only <tt>sequence</tt> is covered here.) To create an instance
 1558:     of <i>nsIRDFContainerUtils</i>, use the following:</p>
 1559: <pre>
 1560: containerUtils = Components.classes['@mozilla.org/rdf/container-utils;1'
 1561: getService(Components.interfaces.nsIRDFContainerUtils);
 1562: </pre>
 1563:     <p>Once you create an anonymous resource, you can create a
 1564:     sequence from it. Then you can test the type of the container
 1565:     and see whether it's empty:</p>
 1566: <pre>
 1567: // create an anonymous resource
 1568: anonResource = RDF.GetAnonymousResource( );
 1569: // create a sequence from that resource
 1570: aSequence = containerUtils.MakeSeq(datasource,anonResource);
 1571: // test the resource
 1572: // (all of these are true)
 1573: isContainer = containerUtils.isContainer(datasource,anonResource);
 1574: isSequence = containerUtils.isSequence(datasource,anonResource);
 1575: isEmpty = containerUtils.isEmpty(datasource,anonResource);
 1576: </pre>
 1577:     <p>Note that the sequence object is not passed into the
 1578:     functions performing the test in the previous example; the
 1579:     resource containing the sequence is passed in. Although
 1580:     <tt>aSequence</tt> and <tt>anonResource</tt> are basically the
 1581:     same resource, their data types are different.
 1582:     <tt>isContainer</tt>, <tt>isSequence</tt>, and <tt>isEmpty</tt>
 1583:     can be used more easily with other RDF functions when a
 1584:     resource is used as a parameter:</p>
 1585: <pre>
 1586: object = datasource.GetTarget(subject,predicate,true);
 1587: if(RDF.isAnonymousResource(object))
 1588: {
 1589: isSeq = containerUtils.IsSeq(datasource,object);
 1590: }
 1591: </pre>
 1592:     <p>The RDF container utilities also provide an indexing
 1593:     function. <tt>indexOf</tt> is useful for checking if an element
 1594:     exists in a container resource:</p>
 1595: <pre>
 1596: indexNumber =
 1597: containerUtils.indexOf(datasource,object,RDF.GetLiteral('Eric'));
 1598: if(index != -1)
 1599: alert('Eric exists in this container');
 1600: </pre>
 1601:     <h3><a name="77104"></a> nsIRDFContainer</h3>
 1602:     <p>This interface <!--INDEX nsIRDFContainer interface --> 
 1603:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFContainer -->
 1604:     <!--INDEX interfaces:RDF:nsIRDFContainer --> provides
 1605:     vector-like access to an RDF container's elements.<a name=
 1606:     "b291"></a><a href="#291">[*]</a> The <i>nsIRDFContainer</i>
 1607:     interface allows you to add, look up, and remove elements from
 1608:     a container once you create it.</p>
 1609:     <h4><a name="77105"></a> Adding an element to a container</h4>
 1610:     <p>You can add an <!--INDEX containers:elements, adding --> 
 1611:     <!--INDEX elements:containers, adding to --> element to a
 1612:     container in two ways. You can append it to the end of the list
 1613:     with <tt>Append</tt> or insert it at a specific place in the
 1614:     container:</p>
 1615: <pre>
 1616: newLiteral = RDF.GetLiteral('Ian');
 1617: aSequence.AppendElement(newLiteral);
 1618: // or
 1619: aSequence.InsertElementAt(newLiteral,3,true);
 1620: </pre>
 1621:     <p>The second attribute in <tt>InsertElementAt</tt> is where
 1622:     the element should be placed. The third attribute specifies
 1623:     that the list can be reordered. This method is useful for
 1624:     working with ordered containers such as sequences. If this
 1625:     locking parameter is set to false and an element already exists
 1626:     at that location, then the existing element is overwritten.</p>
 1627:     <h4><a name="77106"></a> Removing an element from a
 1628:     container</h4>
 1629:     <p>Removing an element from a container works much the same as
 1630:     adding one. The difference is that a reordering attribute is
 1631:     included on <tt>RemoveElement</tt>. If this attribute is set to
 1632:     false, you may have holes in the container, which can create
 1633:     problems when enumerating or indexing elements within.</p>
 1634: <pre>
 1635: newLiteral = RDF.GetLiteral('Ian');
 1636: aSequence.RemoveElement(newLiteral,true);
 1637: // or
 1638: aSequence.RemoveElementAt(newLiteral,3,true);
 1639: </pre>
 1640:     <p>If you use the <tt>indexOf</tt> property of
 1641:     <tt>nsIRDFContainer</tt>, you can also use <tt>GetCount</tt> to
 1642:     learn how many elements are in the container. The count starts
 1643:     at 0 when the container is initialized:</p>
 1644: <pre>
 1645: numberOfElements = aSequence.GetCount( );
 1646: </pre>
 1647:     <p>Once you have the sequence, the datasource and resource the
 1648:     sequence resides in can be retrieved. In effect, these
 1649:     properties look outward instead of toward the data:</p>
 1650: <pre>
 1651: seqDatasource = aSequence.DataSource;
 1652: seqResource = aSequence.Resource;
 1653: </pre>
 1654:     <p>Like many methods in the RDF interfaces, this one allows you
 1655:     to traverse and retrieve any part of the RDF graph.</p>
 1656:     <h3><a name="77107"></a> nsIRDFXML Interfaces</h3>
 1657:     <p>The RDF/XML interfaces are covered only briefly here.
 1658:     Besides being abstract and confusing, these interfaces require
 1659:     a lot of error handling to work correctly. Fortunately, a
 1660:     library on mozdev.org called <i>JSLib</i> handles RDF file
 1661:     access. The <i>JSLib</i> XML library does the dirty work in a
 1662:     friendly manner. See the section <a href="#77112">"JSLib RDF
 1663:     Files</a>," later in this chapter, for more information.</p>
 1664:     <h4><a name="77108"></a> nsIRDFXMLParser and nsIRDFXMLSink</h4>
 1665:     <p><i>nsIRDFXML</i> <!--INDEX nsIRDFXMLParser interface --> 
 1666:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFXMLParser -->
 1667:     <!--INDEX interfaces:RDF:nsIRDFXMLParser --> is the raw RDF/XML
 1668:     parser of Mozilla. Used by Mozilla, its main purpose is to
 1669:     parse an RDF file <!--INDEX parsing:RDF files -->
 1670:     asynchronously as a stream listener. Though this subject is
 1671:     beyond the scope of this book, the interface provides something
 1672:     interesting and useful. The <tt>parseString</tt> function
 1673:     allows you to feed <i>nsIRDFXMLParser</i> a string and have it
 1674:     parse that data as RDF and put it into a datasource, as <a
 1675:     href="#77042">Example 10-9</a> demonstrates.</p>
 1676:     <p><i>Example 10-9: <a name="77042"></a></i> <i>Parse an
 1677:     RDF/XML string into a datasource</i></p>
 1678: <pre>
 1679:  RDF = Components.classes&lt;/td&gt;['@mozilla.org/rdf/rdf-service;1'].
 1680:          getService(Components.interfaces.nsIRDFService);
 1681:  // Used to create a URI below
 1682:  ios = Components.classes&lt;/td&gt;["@mozilla.org/network/io-service;1"].
 1683:        getService(Components.interfaces.nsIIOService);
 1684:  xmlParser = '@mozilla.org/rdf/xml-parser;1';
 1685:  parser = Components.classes&lt;/td&gt;[xmlParser].
 1686:           createInstance(Components.interfaces.nsIRDFXMLParser);
 1687:  uri = ios.newURI("<a href=
 1688: "http://books.mozdev.org/rdf">http://books.mozdev.org/rdf</a>#", null);
 1689:  // Entire RDF File stored in a string
 1690:  rdfString =
 1691:    '&lt;rdf:RDF xmlns:rdf=&lt;/td&gt;<i><a href=
 1692: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#</i>' +
 1693:    'xmlns:b="<a href=
 1694: "http://books.mozdev.org/rdf">http://books.mozdev.org/rdf</a>#"&gt;' +
 1695:    '&lt;rdf:Description about="urn:root"&gt;' + // Rest of file ...
 1696:  parser.parseString(datasource,uri,rdfString);
 1697:  // Parsed string data now resides in the datasource
 1698: </pre>
 1699:     <p>The RDF/XML data that was in the string is a part of the
 1700:     datasource and ready for use (just like any other RDF data in a
 1701:     datasource). The <tt>uri</tt> acts as a base reference for the
 1702:     RDF in case of relative links.</p>
 1703:     <p><i>nsIRDFXMLParser</i> uses <i>nsIRDFXMLSink</i> 
 1704:     <!--INDEX nsIRDFXMLSink interface --> 
 1705:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFXMLSink -->
 1706:     <!--INDEX interfaces:RDF:nsIRDFXMLsink --> for event 
 1707:     <!--INDEX event handling:RDF files --> handling. The interfaces
 1708:     are totally separate, but behind the scenes, they work together
 1709:     with the incoming data. <a href="#77044">Example 10-10</a>
 1710:     shows how a series of events is created in an object and then
 1711:     used to handle parser events. Example 10-10<a name="77044"></a>
 1712:     <i>Setup nsIRDFXMLSink with event handlers</i></p>
 1713: <pre>
 1714:  var Observer = {
 1715:     onBeginLoad: function(aSink)
 1716:     {
 1717:       alert("Beginning to load the RDF/XML...");
 1718:     },
 1719:     onInterrupt: function(aSink) {},
 1720:     onResume: function(aSink) {},
 1721:     onEndLoad: function(aSink)
 1722:     {
 1723:       doneLoading( ); // A function that does something with the datasource
 1724:     },
 1725:    onError: function(aSink, aStatus, aErrorMsg)
 1726:    {
 1727:      alert("Error: " + aErrorMsg);
 1728:    }
 1729:  };
 1730: </pre>
 1731:     <p>Once the event handlers are set up, you can use
 1732:     <i>nsIRDFXMLSink</i>:</p>
 1733: <pre>
 1734: sink = datasource.QueryInterface(Components.interfaces.nsIRDFXMLSink);
 1735: sink.addXMLSinkObserver(observer);
 1736: </pre>
 1737:     <p>The events are then triggered automatically when the
 1738:     datasource is loaded up with data, allowing you to create
 1739:     handlers that manipulate the data as it appears.</p>
 1740:     <h4><a name="77109"></a> nsIRDFXMLSerializer and
 1741:     nsIRDFXMLSource</h4>
 1742:     <p>These two <!--INDEX nsIRDFXMLSerializer interface --> 
 1743:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFXMLSerializer -->
 1744:     <!--INDEX interfaces:RDF:nsIRDFXMLSerializer --> interfaces are
 1745:     meant to work together. <i>nsIRDFXMLSerializer</i> lets you
 1746:     <tt>init</tt> a datasource into the <tt>xml-serializer</tt>
 1747:     module that outputs RDF. However, <i>
 1748:     <!--INDEX nsIRDFXMLSource interface --> 
 1749:     <!--INDEX RDF (Resource Description Framework):interfaces:nsIRDFXMLSource -->
 1750:     <!--INDEX interfaces:RDF:nsIRDFXMLSource -->
 1751:     nsIRDFXMLSource</i> actually contains the <tt>Serialize</tt>
 1752:     function. Here's how to serialize a datasource into an
 1753:     alert:</p>
 1754: <pre>
 1755: serializer = '@mozilla.org/rdf/xml-serializer;1';
 1756: s = Components.classes[serializer].
 1757: createInstance(Components.interfaces.nsIRDFXMLSerializer);
 1758: s.init(datasource);
 1759: output = new Object( );
 1760: output.write = new function(buf,count)
 1761: {
 1762: alert(buf); // Show the serialized syntax
 1763: return count;
 1764: }
 1765: s.QueryInterface(Components.interfaces.nsIRDFXMLSource).Serialize(output);
 1766: </pre>
 1767:     <p>As in the previous example with <i>nsIRDFXMLParser</i>, <a
 1768:     href="#77044">Example 10-10</a> does not use RDF data from a
 1769:     file. The serialized data is passed directly to an alert, which
 1770:     then displays the generated RDF.</p>
 1771:     <h2><a name="77110"></a> Template Dynamics</h2>
 1772:     <p>Once you learn how to create templates and modify
 1773:     datasources, the ultimate in template mastery is to apply
 1774:     datasources to a template dynamically.</p>
 1775:     <p>This process is done through the <tt>database</tt> property
 1776:     of a XUL element that contains a template. The object returned
 1777:     by this property has only two methods, <tt>AddDataSource</tt>
 1778:     and <tt>RemoveDataSource</tt>. A separate
 1779:     <tt>builder.rebuild</tt> function is also available for
 1780:     refreshing the template's display, but you probably won't need
 1781:     it once the template automatically updates itself. The addition
 1782:     and removal of a datasource to a <tt>&lt;tree&gt;</tt> template
 1783:     is demonstrated here:</p>
 1784: <pre>
 1785: tree = document.getElementById('tree-template');
 1786: tree.database.AddDataSource(someDatasource);
 1787: // tree will now update its display to show contents
 1788: tree.database.RemoveDataSource(someDatasource);
 1789: // tree will now be empty
 1790: // Optional, use only when tree is not updating for some reason
 1791: tree.builder.rebuild( );
 1792: </pre>
 1793:     <p>You can add and remove any datasource as long as the
 1794:     template actually matches the data inside it. Also, multiple
 1795:     datasources can be applied to the same template with no
 1796:     problems, which allows you to aggregate data from different
 1797:     places, such as contact data, work information, and computer
 1798:     hardware information (e.g., "Eric uses a Compaq with the serial
 1799:     number 1223456-1091 to write his book and he sits on the fourth
 1800:     floor of the Acme Building, which is the Bay Area branch of
 1801:     Acme Enterprises.)</p>
 1802:     <h3><a name="77111"></a> Template Dynamics in XBL</h3>
 1803:     <p>Putting templates 
 1804:     <!--INDEX XBL (eXtensible Binding Language):templates --> 
 1805:     <!--INDEX templates:XBL --> <!--INDEX datasources:templates -->
 1806:     inside XBL can be a useful organizational scheme. Here is a
 1807:     basic implementation of a widget that creates a list of people
 1808:     based on names listed in an attribute:</p>
 1809: <pre>
 1810: &lt;people names="Brian King,Eric Murphy,Ian Oeschger,Pete Collins,David Boswell"/&gt;
 1811: </pre>
 1812:     <p>Obviously, the comma is used as the delimiter for this list.
 1813:     The constructor element in <a href="#77046">Example 10-11</a>
 1814:     uses JavaScript to break up this string. Example 10-11<a name=
 1815:     "77046"></a> <i>Binding with in-memory datasource and
 1816:     &lt;listbox&gt; template</i></p>
 1817: <pre>
 1818:  &lt;?xml version="1.0"?&gt;
 1819:  &lt;bindings xmlns ="<a href=
 1820: "http://www.mozilla.org/xbl">http://www.mozilla.org/xbl</a>"
 1821:  xmlns:xul="<a href=
 1822: "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul</a>"&gt;
 1823:    &lt;binding id="people"&gt;
 1824:      &lt;implementation&gt;
 1825:        &lt;constructor&gt;
 1826:        &lt;!&lt;/td&gt;[CDATA[
 1827:          // Read the Names into an Array
 1828:          names = document.getAnonymousNodes(this)&lt;/td&gt;[0].getAttribute('names');
 1829:          names = new String(names);
 1830:          namesArray= names.split(',');
 1831:          // Initialize the RDF Service
 1832:          rdf = Components
 1833:               .classes&lt;/td&gt;['@mozilla.org/rdf/rdf-service;1']
 1834:               .getService(Components.interfaces.nsIRDFService);
 1835:          // Initialize a Datasource in Memory
 1836:               inMemory = '@mozilla.org/rdf/datasource;1?name=in-memory-datasource';
 1837:          datasource = Components.classes&lt;/td&gt;[inMemory].
 1838:             createInstance(Components.interfaces.nsIRDFDataSource);
 1839:          // Create the Root Node and an Anonymous Resource to Start With
 1840:          root   = rdf.GetResource('urn:root');
 1841:          people = rdf.GetAnonymousResource( );
 1842:          // Insert the People resource into the RDF graph
 1843:          datasource.Assert
 1844:            (root,
 1845:             rdf.GetResource('<a href=
 1846: "http://www.mozdev.org/rdf">http://www.mozdev.org/rdf</a>#people'),
 1847:             people,true);
 1848:          // Initialize Methods needed for Containers
 1849:          rdfc = Components
 1850:                .classes&lt;/td&gt;['@mozilla.org/rdf/container-utils;1']
 1851:                .getService(Components.interfaces.nsIRDFContainerUtils);
 1852:          // For the People resource, make a Sequence of people
 1853:          peopleSequence = rdfc.MakeSeq(datasource, people);
 1854:          for(i=0;i&lt;namesArray.length;i++)
 1855:          {
 1856:            // Create a Person, with a Unique Number, for example
 1857:            person = rdf.GetResource(i);
 1858:            // Insert the Person's name into the RDF graph underneath number
 1859:            datasource.Assert
 1860:              (person,
 1861:               rdf.GetResource('<a href=
 1862: "http://www.mozdev.org/rdf">http://www.mozdev.org/rdf</a>#name'),
 1863:               rdf.GetLiteral(namesArray&lt;/td&gt;[i]),true);
 1864:            peopleSequence.AppendElement(person);
 1865:          }
 1866:          list = document.getAnonymousNodes(this)&lt;/td&gt;[1];
 1867:          list.database.AddDataSource(datasource);
 1868:        ]]&gt;
 1869:        &lt;/constructor&gt;
 1870:      &lt;/implementation&gt;
 1871:      &lt;content&gt;
 1872:        &lt;xul:box id="names" inherits="names" flex="0"/&gt;
 1873:        &lt;xul:listbox datasources="rdf:null" ref="urn:root" flex="1"&gt;
 1874:          &lt;xul:template&gt;
 1875:            &lt;xul:rule&gt;
 1876:              &lt;xul:conditions&gt;
 1877:                &lt;xul:content uri="?uri"/&gt;
 1878:                &lt;xul:triple subject="?uri"
 1879:                         predicate="<a href=
 1880: "http://www.mozdev.org/rdf">http://www.mozdev.org/rdf</a>#people"                              object="?people"/&gt;
 1881:                &lt;xul:member container="?people" child="?person"/&gt;
 1882:                &lt;xul:triple subject="?person"
 1883:                         predicate="<a href=
 1884: "http://www.mozdev.org/rdf">http://www.mozdev.org/rdf</a>#name"                         object="?name"/&gt;
 1885:              &lt;/xul:conditions&gt;
 1886:              &lt;xul:action&gt;
 1887:                &lt;xul:listitem uri="?person"&gt;
 1888:                  &lt;xul:listcell&gt;
 1889:                    &lt;xul:description value="?person "/&gt;
 1890:                    &lt;xul:description value="?name"/&gt;
 1891:                  &lt;/xul:listcell&gt;
 1892:                &lt;/xul:listitem&gt;
 1893:              &lt;/xul:action&gt;
 1894:            &lt;/xul:rule&gt;
 1895:          &lt;/xul:template&gt;
 1896:        &lt;/xul&gt;
 1897:      &lt;/content&gt;
 1898:    &lt;/binding&gt;
 1899:  &lt;/bindings&gt;
 1900: </pre>
 1901:     <p>In <a href="#77046">Example 10-11</a>, everything you need
 1902:     to display a datasource dynamically is present. The only
 1903:     difference between this dynamically generated version and a
 1904:     static RDF-based template is the
 1905:     <tt>datasources="rdf:null"</tt>, which specifies that the
 1906:     template does not refer to an actual datasource. Data that is
 1907:     edited, rearranged, or changed in a different way is often
 1908:     displayed dynamically in the UI with templates in this
 1909:     manner.</p>
 1910:     <h2><a name="77112"></a> JSLib RDF Files</h2>
 1911:     <p>Working 
 1912:     <!--INDEX STARTRANGE==RDF (Resource Description Framework):files:JSLib -->
 1913:     <!--INDEX STARTRANGE==JSLib libraries:RDF files --> 
 1914:     <!--INDEX STARTRANGE==files:RDF:JSLib --> with actual RDF files
 1915:     is not easy. However, JSLib (<i><a href=
 1916:     "http://jslib.mozdev.org">http://jslib.mozdev.org</a></i>)
 1917:     provides an RDF file library that can help you develop an
 1918:     RDF-based application. The library provides many types of error
 1919:     checking, as well as a friendly abstraction away from the
 1920:     RDF/XML interfaces of Mozilla (see <a href="#77107">"nsIRDFXML
 1921:     Interfaces</a>," later in this chapter). <a href=
 1922:     "#77048">Example 10-12</a> shows some common uses of the
 1923:     <tt>RDFFile</tt> class in JSLib. This functionality can be used
 1924:     in situations in which you have data in RDF that you want to
 1925:     pull out "manually" and use piece by piece (rather than as a
 1926:     whole datasource in a template). Example 10-12<a name=
 1927:     "77048"></a> <i>Creating and modifying an RDF file using
 1928:     JSLib</i></p>
 1929: <pre>
 1930:  var rdfFileURL = 'chrome://jarfly/content/jar.rdf';
 1931:  var gTreeBody = null;
 1932:  var gListbox = null;
 1933:  var gRDF = null;
 1934:  function onload( )
 1935:  {
 1936:    fileUtils = new FileUtils( );
 1937:    path = fileUtils.chrome_to_path(rdfFileURL);
 1938:    if(navigator.platform == "Win32") {
 1939:      path = path.replace(/\//g,"\\");
 1940:      // Only needed on Windows, until JSLib is fixed
 1941:    }
 1942:    gRDF = new RDFFile(path,'jar:flies','<a href=
 1943: "http://mozdev.org/fly-rdf">http://mozdev.org/fly-rdf</a>#');
 1944:    gTreeBody = document.getElementById('tb');
 1945:    gTreeBody.database.AddDataSource(gRDF.dsource);
 1946:    gListbox  = document.getElementById('list');
 1947:    gListbox.database.AddDataSource(gRDF.dsource);
 1948:    rebuildLists( );
 1949:  }
 1950:  function rebuildLists( )
 1951:  {
 1952:    gTreeBody.builder.rebuild( );
 1953:    gListbox.builder.rebuild( );
 1954:  }
 1955:  function update( )
 1956:  {
 1957:    name      = document.getElementById('nameField').value;
 1958:    color     = document.getElementById('colorField').value;
 1959:    quantity  = document.getElementById('quantityField').value;
 1960:    seqNumber = -1;
 1961:    del       = false;
 1962:    replace   = false;
 1963:    if(document.getElementById('delete').checked)
 1964:      del = true;
 1965:    if(document.getElementById('replace').checked)
 1966:      replace = true;
 1967:    var seqLength = 0;
 1968:    if(gRDF.doesSeqExist('types'))
 1969:    {
 1970:      seqLength = gRDF.getSeqSubNodes('types').length;
 1971:      //if(del)gRDF.removeSeq('types',false);
 1972:    }
 1973:    else
 1974:      gRDF.addSeq('types');
 1975:    for(i=0;i&lt;seqLength;i++)
 1976:    {
 1977:      tempItem = 'types:_' + (i+1);
 1978:      if(gRDF.getAttribute(tempItem,'name')==name)
 1979:        seqNumber = gRDF.getAttribute(tempItem,'number');
 1980:    }
 1981:    if(seqNumber == -1)
 1982:    {
 1983:      item = 'types:_' + (seqLength+1);
 1984:      gRDF.setAttribute(item,'name',name);
 1985:      gRDF.setAttribute(item,'number',seqLength+1);
 1986:    }
 1987:    else
 1988:    {
 1989:      item = 'types:_' + seqNumber;
 1990:      gRDF.setAttribute(item,'number',seqNumber);
 1991:    }
 1992:    if(color!='')
 1993:      gRDF.setAttribute(item,'color',color);
 1994:    if(quantity!='')
 1995:    {
 1996:      gRDF.setAttribute(item,'quantity',quantity);
 1997:      gRDF.setAttribute(item,'dead',calcDead(quantity,replace));
 1998:    }
 1999:    if(!del)
 2000:      gRDF.addNode(item);
 2001:    else
 2002:      gRDF.removeNode(item);
 2003:    gRDF.flush( );
 2004:    onload( );
 2005:  }
 2006:  function calcDead(quantity,replace)
 2007:  {
 2008:    if(!replace)
 2009:    {
 2010:      v = parseInt( (quantity * Math.random( )) * 0.13 );
 2011:      return (v.toString( ));
 2012:    }
 2013:    else
 2014:      return 0;
 2015:  }
 2016:  function changeC(color)
 2017:  {
 2018:    document.getElementById('colorField').value=color;
 2019:  }
 2020:  function changeQ(quantity)
 2021:  {
 2022:    document.getElementById('quantityField').value=quantity;
 2023:  }
 2024: </pre>
 2025:     <p>This example contains a datasource that represents a
 2026:     collection of flies. These flies are built up dynamically with
 2027:     JavaScript objects from the RDF library, which represent the
 2028:     datasource itself (<tt>gRDF = new RDFFile</tt>), methods that
 2029:     view and update the data
 2030:     (<tt>if(gRDF.getAttribute(tempItem,'name')==name</tt>), and
 2031:     utilities that make work with RDF files easier (<tt>path =
 2032:     fileUtils.chrome_to_path(rdfFileURL)</tt>).</p>
 2033:     <p><a href="#77050">Example 10-13</a> initializes and updates a
 2034:     file after it changes. Example 10-13<a name="77050"></a>
 2035:     <i>Initialization</i></p>
 2036: <pre>
 2037:  var rdfFileURL = 'chrome://jarfly/content/jar.rdf';
 2038:  var gTreeBody = null;
 2039:  var gListbox = null;
 2040:  var gRDF = null;
 2041:  function onload( )
 2042:  {
 2043:    fileUtils = new FileUtils( );
 2044:    path = fileUtils.chrome_to_path(rdfFileURL);
 2045:    if(navigator.platform == "Win32") {
 2046:      path = path.replace(/\//g,"\\");
 2047:      // Only needed on Windows, until JSLib is fixed
 2048:    }
 2049:    gRDF = new RDFFile(path,'jar:flies','<a href=
 2050: "http://mozdev.org/fly-rdf">http://mozdev.org/fly-rdf</a>#');
 2051: </pre>
 2052:     <p>In <a href="#77050">Example 10-13</a>, the file URL is set
 2053:     to an RDF file in the chrome area. Note that both a
 2054:     <tt>&lt;tree&gt;</tt> and a <tt>&lt;listbox&gt;</tt>, which
 2055:     display the same data in different ways, will be updated with
 2056:     the same datasource. The <tt>onload</tt> function is called
 2057:     after the main XUL document is loaded. A class called
 2058:     <tt>FileUtils</tt> is initialized, which will create a path to
 2059:     the RDF file. If the file doesn't already exist, JSLib
 2060:     automatically creates it.</p>
 2061:     <p>Finally, the <tt>RDFFile</tt> is created by using the path
 2062:     and a root resource identifier, and the "xFly" namespace is
 2063:     used for the data references. <a href="#77052">Example
 2064:     10-14</a> shows that the RDF file is ready to have its data
 2065:     added and deleted. Example 10-14<a name="77052"></a> <i>Data
 2066:     updating</i></p>
 2067: <pre>
 2068:  function update( )
 2069:  {
 2070:    ...
 2071:    var seqLength = 0;
 2072:    if(gRDF.doesSeqExist('types'))
 2073:    {
 2074:      seqLength = gRDF.getSeqSubNodes('types').length;
 2075:      //if(del)gRDF.removeSeq('types',false);
 2076:    }
 2077:    else
 2078:      gRDF.addSeq('types');
 2079:    for(i=0;i&lt;seqLength;i++)
 2080:    {
 2081:      tempItem = 'types:_' + (i+1);
 2082:      if(gRDF.getAttribute(tempItem,'name')==name)
 2083:        seqNumber = gRDF.getAttribute(tempItem,'number');
 2084:    }
 2085:    if(seqNumber == -1)
 2086:    {
 2087:      item = 'types:_' + (seqLength+1);
 2088:      gRDF.setAttribute(item,'name',name);
 2089:      gRDF.setAttribute(item,'number',seqLength+1);
 2090:    }
 2091:    else
 2092:    {
 2093:      item = 'types:_' + seqNumber;
 2094:      gRDF.setAttribute(item,'number',seqNumber);
 2095:    }
 2096:    if(color!='')
 2097:      gRDF.setAttribute(item,'color',color);
 2098:    if(quantity!='')
 2099:    {
 2100:      gRDF.setAttribute(item,'quantity',quantity);
 2101:      gRDF.setAttribute(item,'dead',calcDead(quantity,replace));
 2102:    }
 2103:    if(!del)
 2104:      gRDF.addNode(item);
 2105:    else
 2106:      gRDF.removeNode(item);
 2107:    gRDF.flush( );
 2108:    onload( );
 2109: </pre>
 2110:     <p><a href="#77052">Example 10-14</a> contains a modified
 2111:     version of the <tt>update</tt> function. First, the function
 2112:     checks to see if a sequence called <tt>types</tt> is in the RDF
 2113:     file. If not, it creates one. Next, it appends an item to the
 2114:     sequence using <tt>type:_+(seqLength+1)</tt>. The same type of
 2115:     container setup was described in the section <a href=
 2116:     "#77104">"nsIRDFContainer</a>," earlier in this chapter.</p>
 2117:     <p>The <tt>update</tt> function then adds the color, quantity,
 2118:     and "dead" properties of that new item in the sequence. Next,
 2119:     it ensures that you actually want to add the item to the RDF
 2120:     file and flushes it out if not. It then recalls the
 2121:     <tt>onload</tt> function to update the template display.</p>
 2122:     <p>These are the basics of using <tt>RDFFile</tt>. As you can
 2123:     see, using JSLib for RDF is often much easier than trying to
 2124:     implement a similar setup on your own. More information about
 2125:     <tt>RDFFile</tt> and the other JSLib libraries can 
 2126:     <!--INDEX web sites:JSLib --> be 
 2127:     <!--INDEX ENDRANGE==RDF (Resource Description Framework):files:JSLib -->
 2128:     <!--INDEX ENDRANGE==JSLib libraries:RDF files --> 
 2129:     <!--INDEX ENDRANGE==files:RDF:JSLib --> found at <i><a href=
 2130:     "http://jslib.mozdev.org/">http://jslib.mozdev.org/</a></i>.</p>
 2131:     <h2><a name="77113"></a> Manifests</h2>
 2132:     <p>The package 
 2133:     <!--INDEX RDF (Resource Description Framework):manifest files -->
 2134:     <!--INDEX manifests:RDF --> descriptions, generally called
 2135:     <i>manifests</i>, use RDF to describe new packages and files to
 2136:     Mozilla. They can be added seamlessly because RDF provides a
 2137:     platform-like environment that facilitates the installation and
 2138:     use of new Mozilla software.</p>
 2139:     <p>All packages, including the ones that come preinstalled with
 2140:     Mozilla (such as the browser, the MailNews component, and the
 2141:     en-US language pack), have manifests describing them in terms
 2142:     of their relation to other packages. The manifests are
 2143:     typically files called <i>contents.rdf</i>, but they may also
 2144:     be called <i>manifest.rdf</i>. <a href="#77054">Example
 2145:     10-15</a> presents a <i>contents.rdf</i> file that describes a
 2146:     new skin for Mozilla. Example 10-15<a name="77054"></a> <i>Skin
 2147:     manifest</i></p>
 2148: <pre>
 2149:  &lt;?xml version="1.0"?&gt;
 2150:  &lt;RDF:RDF xmlns:RDF="&lt;/td&gt;<i><a href=
 2151: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#</i>"
 2152:    xmlns:chrome="&lt;/td&gt;<i><a href=
 2153: "http://www.mozilla.org/rdf/chrome">http://www.mozilla.org/rdf/chrome</a>#</i>"&gt;
 2154:  &lt;!-- List all the skins being supplied by this theme --&gt;
 2155:  &lt;RDF:Seq about="urn:mozilla:skin:root"&gt;
 2156:    &lt;RDF:li resource="urn:mozilla:skin:modern/1.0" /&gt;
 2157:  &lt;/RDF:Seq&gt;
 2158:  &lt;!-- Modern Information --&gt;
 2159:  &lt;RDF:Description about="urn:mozilla:skin:modern/1.0"
 2160:    chrome:displayName="Modern"
 2161:    chrome:author="&lt;/td&gt;<i><a href=
 2162: "MAILTO:themes@mozilla.org">themes@mozilla.org</a></i>"
 2163:    chrome:name="&lt;/td&gt;<i><a href=
 2164: "MAILTO:themes@mozilla.org/modern/1.0">themes@mozilla.org/modern/1.0</a></i>"&gt;
 2165:  &lt;chrome:packages&gt;
 2166:    &lt;RDF:Seq about="urn:mozilla:skin:modern/1.0:packages"&gt;
 2167:      &lt;--RDF:li resource="urn:mozilla:skin:modern/1.0:aim"/ --&gt;
 2168:      &lt;RDF:li resource="urn:mozilla:skin:modern/1.0:communicator"/&gt;
 2169:      &lt;RDF:li resource="urn:mozilla:skin:modern/1.0:editor"/&gt;
 2170:      &lt;RDF:li resource="urn:mozilla:skin:modern/1.0:global"/&gt;
 2171:      &lt;RDF:li resource="urn:mozilla:skin:modern/1.0:messenger"/&gt;
 2172:      &lt;RDF:li resource="urn:mozilla:skin:modern/1.0:navigator"/&gt;
 2173:    &lt;/RDF:Seq&gt;
 2174:  &lt;/chrome:packages&gt;
 2175:  &lt;/RDF:Description&gt;
 2176:  &lt;/RDF:RDF&gt;
 2177: </pre>
 2178:     <p>As you can see, the manifest is divided up into sections.
 2179:     After the preamble, where the XML processing instruction and
 2180:     the namespace declarations are made, an RDF sequence lists all
 2181:     the themes defined or supplemented (since you can create a
 2182:     package updated for only one Mozilla component, such as the
 2183:     browser) by this package. This section contains only one
 2184:     <tt>RDF:li-</tt>the modern theme.</p>
 2185:     <p>The next section gives more information on the theme, such
 2186:     as the author, the theme name, and a description. The
 2187:     <tt>chrome:packages</tt> structure that completes the manifest
 2188:     describes the packages to which this theme should be applied.
 2189:     All major components of the Netscape browser are listed in this
 2190:     example-including the AIM client that is not a part of
 2191:     Mozilla-but is skinned by themes such as Modern.</p>
 2192:     <h3><a name="77114"></a> RDF and Dynamic Overlays</h3>
 2193:     <p>Manifests can <!--INDEX dynamic overlays:RDF --> 
 2194:     <!--INDEX overlays:RDF --> 
 2195:     <!--INDEX RDF (Resource Description Framework):manifest files:dynamic overalys and -->
 2196:     <!--INDEX manifests:RDF:dynamic overlays and --> also add new
 2197:     menu items to existing Mozilla menus. When you add a new
 2198:     package to Mozilla, you should make it accessible from within
 2199:     the browser application, where users can access it easily. This
 2200:     is where RDF and dynamic overlays come in.</p>
 2201:     <p>The RDF you provide in your package makes it possible for
 2202:     the chrome registry, discussed in <a href=
 2203:     "ch06.html#77063">Chapter 6</a>, to find, understand, and
 2204:     register your new files. Packages must be registered if they
 2205:     are to be skinned, localized, or accessed using the special
 2206:     tools Mozilla provides (e.g., the chrome URL or XPConnect to
 2207:     the XPCOM libraries). If you do not register your package by
 2208:     providing the necessary RDF manifests, it cannot be accessed
 2209:     except as a disparate collection of files in the browser's main
 2210:     content window, which is not what you want.</p>
 2211:     <p>You can add overlays in Mozilla in two ways: import them
 2212:     explicitly by using an overlay processing instruction at the
 2213:     top of the XUL file into which items in the overlay file are to
 2214:     be "composed," or use RDF to register and load overlay files at
 2215:     runtime. This latter method will be used here to add an "xFly"
 2216:     item to the Tools menu of the Mozilla suite of
 2217:     applications.</p>
 2218:     <p><a href="#77056">Example 10-16</a> shows the
 2219:     <i>contents.rdf</i> manifest format that alerts Mozilla of the
 2220:     presence of an overlay, its target in the Mozilla application,
 2221:     and the package of which it is a part. Example 10-16<a name=
 2222:     "77056"></a> <i>Overlay for a sample application menu</i></p>
 2223: <pre>
 2224:  &lt;?xml version="1.0"?&gt;
 2225:  &lt;RDF:RDF xmlns:RDF="<a href=
 2226: "http://www.w3.org/1999/02/22-rdf-syntax-ns">http://www.w3.org/1999/02/22-rdf-syntax-ns</a>#"
 2227:           xmlns:chrome="<a href=
 2228: "http://www.mozilla.org/rdf/chrome">http://www.mozilla.org/rdf/chrome</a>#"&gt;
 2229:    &lt;RDF:Seq about="urn:mozilla:package:root"&gt;
 2230:      &lt;RDF:li resource="urn:mozilla:package:help"/&gt;
 2231:    &lt;/RDF:Seq&gt;
 2232:    &lt;RDF:Description about="urn:mozilla:package:help"
 2233:          chrome:displayName="xFly Application"
 2234:          chrome:author="xfly.mozdev.org"
 2235:          chrome:name="xfly"&gt;
 2236:    &lt;/RDF:Description&gt;
 2237:    &lt;!-- Declare overlay points used in this package --&gt;
 2238:    &lt;RDF:Seq about="urn:mozilla:overlays"&gt;
 2239:      &lt;RDF:li resource="chrome://communicator/content/tasksOverlay.xul" /&gt;
 2240:    &lt;/RDF:Seq&gt;
 2241:    &lt;/td&gt;&lt;RDF:Seq about="chrome://communicator/content/tasksOverlay.xul"&gt;
 2242:      &lt;RDF:li&gt;chrome://xfly/content/xflyOverlay.xul&lt;/RDF:li&gt;
 2243:    &lt;/RDF:Seq&gt;
 2244:  &lt;/RDF:RDF&gt;
 2245: </pre>
 2246:     <p>The manifest in <a href="#77056">Example 10-16</a> names the
 2247:     file <i>xflyOverlay.xul</i> as an overlay. Then it names
 2248:     <i>tasksOverlay.xul</i> as the base file into which the
 2249:     contents are placed. In this case, the overlays can overlay
 2250:     other overlay files arbitrarily. An overlay can define new
 2251:     content anywhere in the application. Overlays are often
 2252:     responsible for putting new items in menus. As long as the
 2253:     target and overlay <tt>id</tt>s match, any two RDF datasources
 2254:     are merged. You can try this example by putting a single new
 2255:     menu item in an overlay structure like the one shown in <a
 2256:     href="#77058">Example 10-17</a>. Save it as
 2257:     <i>xflyOverlay.xul</i> in the <i>xfly</i> content subdirectory
 2258:     and use the manifest information in <a href="#77056">Example
 2259:     10-16</a> as part of the packaging process described in <a
 2260:     href="ch06.html#77063">Chapter 6</a>. Example 10-17<a name=
 2261:     "77058"></a> <i>Overlay for an xFly menu item in the
 2262:     browser</i></p>
 2263: <pre>
 2264:  &lt;?xml version="1.0"?&gt;
 2265:  &lt;overlay id="xflyMenuID"
 2266:          xmlns:html="<a href=
 2267: "http://www.w3.org/1999/xhtml">http://www.w3.org/1999/xhtml</a>"
 2268:          xmlns="<a href=
 2269: "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul</a>"&gt;
 2270:    &lt;menupopup id="tools_menu"&gt;
 2271:      &lt;menuitem label="xfly xml editor"
 2272:          oncommand="toOpenWindowByType('mozilla:xfly, 'chrome://xfly/content/');" /&gt;
 2273:  &lt;/menupopup&gt;
 2274:  &lt;/overlay&gt;
 2275: </pre>
 2276:     <p>The <tt>menupopup</tt> in Mozilla with the ID "tools_menu"
 2277:     gets a new menu item when this overlay is processed and its
 2278:     content included.</p>
 2279:     <hr>
 2280:     <hr>
 2281:     <a name="291"></a><a href="#b291">[Back]</a> <a name=
 2282:     "77060"></a> A vector, for those who don't know, is a flexible
 2283:     and more accessible version of the array data structure. 
 2284:     <hr>
 2285:     <br>
 2286:     <br>
 2287:     File a <a href=
 2288:     "http://mozdev.org/bugs/enter_bug.cgi?product=books">Bug</a>
 2289:     for chapter 10. <!-- ?php require(NOTES); ? -->
 2290:     <?php $post_to_list=NO; $author='reviewers@mozdev.org'; $target_page='ch10'; require(NOTES); ?>

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