File Xml000550.htm
June 10, 2000
I maintain a consolidated index of hyperlinks to all of my XML articles at my personal website so that you can access earlier articles from there.
Rendering XML documents
As of this writing, Microsoft IE5 is the only widely-used web browser that has the ability to render XML documents.
IE5 can render XML documents using either CSS (see my personal website) or XSL. This is one in a series of articles that discuss the use of XSL for the rendering of XML documents, with particular emphasis on the use of IE5 for that purpose.
According to one well known author, "The W3C is a consortium, a gathering place where organizations can meet and work together without the appearance of antitrust problems."
I wrote an article addressing this question late in 1999. You can view that article at my personal website if you would like to know more about the W3C.
For purposes of this article, the W3C is a governing body that has published many important documents on XSL and XSLT, two of which will be referred to shortly.
According to the W3C,
| XSL
is a language for expressing stylesheets. It consists of two parts:
1. A language for transforming XML documents, and 2. An XML vocabulary for specifying formatting semantics. An XSL stylesheet specifies the presentation of a class of XML documents by describing how an instance of the class is transformed into an XML document that uses the formatting vocabulary. |
A working draft
As of March 2000, the XSL document is classified as a working draft, so we need to be aware that things could change in the future.
Separating content from presentation
In other words, an XML document contains structured information, but does not provide any hints as to how that information should be rendered for the benefit of a consumer.
An example
For example, if the information happens to be the daily news, there are at least two desirable ways to render the information:
The two different renderings of the same information are likely to be very different. For example, the online version is likely to make extensive use of color. However, due to the cost of printing color, the printed version is likely to make minimal use of color.
I wish printed newspapers could have hyperlinks
The printed version is likely to have statements such as "continued on page 5" (don't you just hate that) at the bottom of the columns. (Then you have an opportunity to drag the bottom of the newspaper through your oatmeal as you manually turn it to a different page.)
Online newspapers do have hyperlinks
The online version for a particular news story may not be broken into different sections. If it is broken into different sections, they will likely be connected with hyperlinks making navigation easy.
Actually, the online newspapers that I read do break a story into different sections. One is usually a summary and other is usually the full story, and the two are connected using hyperlinks.
According to the
W3C,
| This
specification defines the syntax and semantics of XSLT, which is a language
for transforming XML documents into other XML documents.
XSLT is designed for use as part of XSL, which is a stylesheet language
for XML. In addition to XSLT, XSL
XSLT is also designed to be used independently of XSL. However, XSLT is not intended as a completely general-purpose XML transformation language. Rather it is designed primarily for the kinds of transformations that are needed when XSLT is used as part of XSL. |
This is a recommendation from W3C
As of November, 1999, this document is classified as a recommendation by the W3C. This means that "It is a stable document and may be used as reference material or cited as a normative reference from other documents."
Transforming XML to other formats
Because an HTML document can be represented as an XML document, XSLT can be used to transform XML documents into HTML documents.
Suitable for rendering in a Web browser
This makes it possible to render the information contained in an XML document using a common HTML Web browser.
Because of the usefulness of this approach, transforming XML documents into HTML documents will be a primary emphasis in the next several articles.
Where does the transformation take place?
When transforming information from an XML document for rendering on an HTML browser, the transformation can take place anywhere between the XML document and the browser.
Transforming on the server
For example, an XSLT engine could be written in Java and run as a servlet (see the discussion of XT later), or it could be written as a JavaBean component and accessed from a scriptlet in a JavaServer page. (I have written several articles on Java servlets, JavaBean components, and JavaServer pages, which you will find indexed at my personal website.)
Transforming at the browser
Or, the transformation could be performed at the browser. For example, Microsoft IE5 can be used for this purpose.
According to Microsoft,
| The
World Wide Web Consortium (W3C) Working Draft for XSL divides the language
into two main parts: a transformation language for XML documents, and an
XML vocabulary for formatting semantics.
Microsoft® Internet Explorer 5 supports a subset of the transformation part of the Extensible Stylesheet Language (December 18th Working Draft) . Microsoft plans to update this technology to match the final W3C recommendation for XSL. XSL Working Draft Conformance Notes details the differences between the Internet Explorer 5 implementation and the December draft. |
When you press a Process button, the XSL is applied to the XML to convert the XML into HTML.
You can see the HTML that is produced
A major advantage of this approach is that you are able see the HTML that is produced.
Not current
Unfortunately, as of this writing, the site contains the following warning:
| "Sparse
is not current with the latest XSL draft released from the W3C! I am currently
looking at the latest draft to determine if it's worth working on
this any more.
For now, enter some XML and OLD XSL rules and hit process, then you'll see an alert box showing the HTML, and then a window displaying it." |
I personally hope that the author decides to continue updating Sparse as a service to the rest of us who are struggling with XSL and XSLT. Maybe if enough of us send him messages of encouragement, he will decide to do so.
Intermediate HTML is not immediately available with IE5
Unfortunately, if it is possible to get an intermediate copy of the HTML that is produced in IE5, I haven't figured out how to do it (but there is a workaround to get it as described below).
When you apply XSLT code to XML using IE5, the resulting HTML is rendered in the browser window. If you then view the source, what you see is the original XML, not the resulting HTML that is actually rendered.
A lot better than nothing
That's a lot better than nothing. At least Microsoft seems to be serious about supporting XML in its browser. But, for testing purposes, it would be even better if we could see the HTML that is produced.
HTML output is a single line of text
Unfortunately, the entire output HTML file is presented as a single line of text, which is not very suitable for reading.
Copy to clipboard and manually reformat
You can copy the output HTML to the clipboard, paste it into a text editor, and manually insert some line breaks to get a better look at it.
That is fairly labor intensive for a large HTML file, so if I find myself using it very much, I will probably write a short Java or Python program to automatically reformat it into a more readable form.
Use as a debugger
As a debugger, the program provides the ability to single-step through
the code, set breakpoints, etc. Here is the documentation that is
provided with the program:
| "Description:
The XSL Debugger is a simple HTML-based debugger that allows single-stepping through the execution of an XSL stylesheet. The current positions in both the stylesheet and the XML document are indicated, and breakpoints can be set and cleared. Compatibility/Platform Compatibility:
|
IE5 or later is required
When you download and install the XSL Debugger, you will end up with an HTML file named xsl-debugger.htm. (It wants to install itself into a directory named Workshop.)
Usage instructions
To run the debugger,
The output
If the transformation runs successfully, the same output will be produced that you would normally see in your IE5 window.
At that point, you can check a box and cause the HTML that produced that output to be displayed as described above.
Won't work with Netscape 4.7
If you try using the debugger with Netscape 4.7, it won't work.
Errors
If either the XML file or the XSLT file is not well-formed, the debugger will refuse to load the file and will give you some diagnostic information.
Here is what the Clark has to say about XT:
| XT
is an implementation in Java of XSL Transformations. This version of XT
implements the PR-xslt-19991008 version of XSLT. Stylesheets written
for earlier versions of the XSLT WD must be converted before they can be
used with this version of XT.
... XT can be used as a servlet. This requires a servlet engine that implements at least version 2.1 of the Java Servlet API. |
Hooray for servlets
Because of my strong interest in Java (see my personal website), I am particularly interested in using an XSLT engine as either a servlet or as a JavaBean component for transformation of XML data to some other form on the server.
Although I haven't tried XT yet, I plan to do so in the near future.
Until next time ... enjoy your online learning experience.
Copyright 2000, Richard G. Baldwin. Reproduction in whole or in part in any form or medium without express written permission from Richard Baldwin is prohibited.
Richard has participated in numerous consulting projects involving Java, XML, or a combination of the two. He frequently provides onsite Java and/or XML training at the high-tech companies located in and around Austin, Texas. He is the author of Baldwin's Java Programming Tutorials, which has gained a worldwide following among experienced and aspiring Java programmers. He has also published articles on Java Programming in Java Pro magazine.
Richard holds an MSEE degree from Southern Methodist University and has many years of experience in the application of computer technology to real-world problems.
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