Annotation of books/www/articles/xpfe_dhtml.html, revision 1.12

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