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                      3: <title>XPFE vs. DHTML</title>
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                      6: 
                      7: <h2>XPFE vs. DHTML</h2>
                      8: 
                      9: <p>'In the beginning, there were 3 front ends: Mac, Windows and Unix.  Each took a suite of developers to maintain.
                     10: Adding a new feature (even just a button) required 3 engineers to waste at least a day (more often a week) slaving 
                     11: away until the feature was complete.  This had to change.'  This is an 
                     12: <a href="http://www.mozilla.org/xpfe/ElevatorTouchyFeely.html">explanation posted</a> on mozilla.org describing 
                     13: how the Netscape 4.x browsers required a different set of engineers to create and maintain the interface code for
                     14: Netscape on each different platform, even though each version looked nearly identical.
                     15: 
                     16: <p>For an organization committed to creating an application that runs on a range of 
                     17: <a href="http://www.mozilla.org/ports/">different platforms</a> this 
                     18: system of using platform specific code was a huge investment and a big waste of time.  XPFE, Mozilla's 
                     19: cross-platform front end, was designed to fix this by allowing engineers to be able to create one interface that would then
                     20:  work on any operating system.  This new technology started out as a time-saving technique and then turned into one
                     21:  of Mozilla's most powerful innovations.
                     22: 
                     23: <p>Mozilla engineers were trying to create a more efficient process that would save them time and effort when
                     24: they started work on XPFE, but this technology ended up having the unintended consequence of lowering the barriers
                     25: to entry for application developers.  Mike Cornall, in 
                     26: <a href="http://linuxtoday.com/news_story.php3?ltsn=2000-07-25-001-07-OP-SM-0036">an article</a> about Mozilla 
                     27: published on LinuxToday, summarizes the history of XPFE well when he says: 'The application platform capabilities
                     28: of Mozilla came about through a happy coincidence of Open Source development, good design, and far-sighted
                     29: developers who were paying attention.'
                     30: 
                     31: <p>All browsers allow people using any type of computer to access applications on the 
                     32: Web, such as Yahoo! Mail, Amazon and Ebay. Mozilla is simply building on this idea.  
                     33: Using new technologies in conjunction with existing Web standards Mozilla enables the creation of 
                     34: more powerful applications, so instead of using Opera, Netscape 4.x or Internet Explorer 
                     35: to access a Web page you can use a full-featured application with Mozilla.
                     36: 
                     37: <p><b>Understanding XPFE</b>
                     38: 
                     39: <p>The technologies that XPFE uses are all existing Web standards, such as Cascading Style Sheets, JavaScript and
                     40:  XML (the XML component is a new language called XUL, the XML-based User Interface Language).  Since well understood
                     41:  Web standards are being used to create applications instead of platform-specific C code, a whole new group of people
                     42:  now have the ability to create their own applications using Mozilla.
                     43: 
                     44: <p>In the sense that XPFE uses some of the same standards that are used to create Web pages, Mozilla-based
                     45:  applications can even be thought of as Web pages.  Gecko, the HTML rendering engine that Mozilla uses, also draws
                     46:  all XPFE content, so a Web page and an application created with XPFE are on one level treated the same way by 
                     47: Mozilla itself.
                     48: 
                     49: <p>Web developers and designers who use Mozilla are naturally attracted to the fact that they can create
                     50:  applications using the same skills and techniques that they used to create Web pages in the past.  The specifics
                     51:  involved with creating Mozilla applications are different but should seem very familiar to anyone who has created
                     52:  for the Web before.
                     53: 
                     54: <p>When talking about front ends it is important to clarify what this means.  In this context a front end is more
                     55:  than the look and feel of a Mozilla-based application, but includes the functionality and structure of that application
                     56:  as well.  More simply put, XPFE allows users to do more than just create a skin for an application.  For example,
                     57:  Netscape 6 does use this functionality to allow for the creation of 
                     58: <a href="http://www.netscape.com/themes/">different themes</a> for their browser suite, but the browser suite itself
                     59:  is also created out of these same technologies.
                     60: 
1.3       david      61: <p><img src="http://books.mozdev.org/screenshots/moz_0101.gif"><br>
1.2       david      62: <i>Figure 1: XPFE Framework</i>
                     63: 
1.1       david      64: <p>To understand all of the capabilities of XPFE, we can look at how the different components of it fit together.  
                     65: JavaScript is used to create the functionality for a Mozilla-based application, Cascading Style Sheets are used for 
                     66: formatting the look and feel, and XUL is used for creating the application's structure.  Viewed together these three 
                     67: standards can be seen forming the triangle in Figure 1 above.
                     68: 
                     69: <p><b>Comparing XPFE and DHTML</b>
                     70: 
                     71: <p>In many ways XPFE is very similar to <a href="http://www.webreference.com/dhtml/">DHTML</a>.  Dynamic HTML is 
                     72: a combination of HTML with JavaScript and CSS that allows a developer to create a Web application that is contained
                     73:  within the content area of a browser.  XPFE provides a logical evolution to this idea by allowing the creation of
                     74:  applications that are more powerful, more flexible and that can live outside of the browser window as stand-alone
                     75:  programs.
                     76: 
                     77: <p>Figure 2 below illustrates the similarities between XPFE and DHTML.  Both use JavaScript to create functionality, both
                     78:  use CSS to format the design and layout, and both use a fairly simple mark-up language to describe content.  The 
                     79: difference between the two is that one of these mark-up languages is HTML and the other is XUL.
                     80: 
1.4     ! david      81: <p><img src="http://books.mozdev.org/screenshots/moz_0102.gif"><br>
        !            82: <i>Figure 2: Comparison of DHTML and XPFE</i>
1.1       david      83: 
                     84: <p>Although HTML has been put to many different uses, it was <a href="http://www.w3.org/MarkUp/#historical">originally designed</a>
                     85:  as a simple system to link together separate text documents on the Internet.  Later additions to the HTML standard 
                     86: have extended its functionality, but even these enhancements can't make it an appropriate language to use for developing 
                     87: applications.  XUL is a language specifically designed for creating user interfaces, so it makes sense that XPFE is more 
                     88: suited for application development than DHTML.
                     89: 
                     90: <p>Fortunately since XUL as a language is structurally similar to HTML it is simple enough to learn if you are already
                     91:  familiar with the basic language of the Web.  Even if you have never used HTML before, XUL uses a straight-forward 
                     92: <a href="http://www.mozilla.org/xpfe/xulref/">collection of tags</a> that makes it easy to get comfortable with it in 
                     93: a short time.  Once you become accustomed to using XUL you will be ready to start using XPFE to create your own applications.
                     94: 
                     95: <p><b>Oversimplifying in the Metaphor</b>
                     96: 
                     97: <p>This overview of XPFE as a simple evolution of DHTML is an oversimplification of the story and deliberately leaves 
                     98: out much important information.  These details were ignored at first to give a conceptual framework for understanding 
                     99: the new ideas that XPFE represent.  Now that we've gotten past the basics, we can go back and talk about the rest of the 
                    100: functionality available with using Mozilla to create applications.
                    101: 
                    102: <p>At the <a href="http://meetzilla.mozdev.org/second_meeting.html">Second Mozilla Developer Meeting</a>, Rob Ginda, 
                    103: the creator of ChatZilla, lead a discussion group about Mozilla as Platform.  In this session he listed all of the following 
                    104: as components of a Mozilla-based application:</P>
                    105: 
                    106: <FONT COLOR="#800000">
                    107: <UL>
                    108: <LI>XUL (XML-based User Interface Language) - Used to create the structure and content of an application.<br><br>
                    109: <LI>CSS (Cascading Style Sheets) - Used to create the look and feel of an application.<br><br>
                    110: <LI>JavaScript - Used to create the functionality of an application.<br><br>
                    111: <LI>XPInstall (Cross-Platform Install) - Used to package applications so that they can be installed on any platform.<br><br>
                    112: <LI>RDF (Resource Description Framework) - Used to store data and transmit information.  Generally regarded to be one of the most complicated aspects of XPFE.<br><br>
                    113: <LI>DTD (Document Type Definition) - Used for localization and internationalization, more commonly referred to in short-hand as L12N and I18N respectively.<br><br>
                    114: <LI>XBL (eXtensible Binding Language) - Used to create reusable widgets using a combination of XUL and JavaScript.<br><br>
                    115: <LI>XUL templates - Used to create a framework for importing data into an application with a combination of RDF and XUL.<br><br>
                    116: <LI>XPCOM/XPConnect - Used to allow JavaScript, or potentially any other scripting language, to access and utilize C and C++ libraries.
                    117: </UL>
                    118: </FONT>
                    119: 
                    120: <p>Each of these technologies is important and several of these deserve to have whole books devoted to them.  Although
                    121:  each of these technologies is important there is a distinction to be made among them.  Some of these are essential to 
                    122: the creation of a Mozilla application and some of them provide powerful extra features that can be used in addition to 
                    123: the basic functionality.
                    124: 
                    125: <p>For example, <a href="http://www.mozilla.org/rdf/doc/">RDF</a> is an extremely powerful technology for
                    126:  using data in Mozilla but it is possible to create an application without using it.  
                    127: <a href="http://www.mozilla.org/projects/l10n/mlp.html">Localization</a> also provides Mozilla with a great amount 
                    128: of flexibility and usability but there are many existing applications that don't take advantage of this feature.  
                    129: It wouldn't be possible to create an application without XUL though.
                    130: 
                    131: <p><b>Judge For Yourself</b>
                    132: 
                    133: <p>XPFE is a new technology that has yet to prove itself to the Web community and many people are skeptical 
                    134: about the need for an application framework such as this.  Before you make up your mind about XPFE, you should 
                    135: take a look at the many different applications that have already been created using Mozilla so you can judge for 
                    136: yourself.  
                    137: 
                    138: <p>If you are interested in trying out some of these, there are currently over 30 different Mozilla-based 
                    139: applications being hosted on <a href="http://www.mozdev.org/projects.html">mozdev.org</a> that have been created using XPFE.  
                    140: Other applications using the same technology include ActiveState's 
                    141: <a href="http://www.activestate.com/ASPN/Downloads/Komodo/More">Komodo</a> IDE,  Rob Ginda's 
                    142: <a href="http://www.hacksrus.com/~ginda/chatzilla/">ChatZilla</a> IRC client, and Zope's 
                    143: <a href="http://www.zope.org/Resources/Mozilla/">Mozilla Initiative</a>.
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