XSLT Powers a New Wave of Web Applications

Cameron introduces XSLT and shows why it's such a hot topic in application development.
One Language, Many Applications

Suppose you're responsible for a web site of tens of thousands of pages. You maintain those pages in an organization-specific XML vocabulary that strips out formatting information and HTML blemishes; your documents hold only the logical content specific to each page. Visitors need HTML, of course, but you generate that automatically, along with standard headers, frames, navigation bars, footnotes and all the other decorations we've come to expect on the Web. XSLT gives you the ability to update site style instantaneously for all the thousands of managed documents. Moreover, it partitions responsibility nicely between XML content files and XSLT stylesheets, so that different specialists can collaborate effectively.

That executive-level description masks quite a bit of implementation variability. Where and when does the XSLT transformation take place? You might have a back end of XML documents, which you periodically process with a command-line XSLT interpreter to generate static HTML documents served up by a conventional web server. You might keep the XML sources in a database, from which they're retrieved either as XML, as transformed HTML or even as full-blown HTTP sessions. Various application servers, content managers and even XML databases provide each of these interfaces. Another variation is this: you might keep only sources on your server and, with the right combination of HTML extensions and browser, direct the browser itself to interpret the XSLT you pass. You can make each of these steps as dynamic as you like, with caching to improve performance, customization to match browser or reader characteristics and so on.

This multiplicity of applications makes vendor literature a challenge to read. We all adopt different styles of Java programming depending on whether we're working on applets, servlets, beans and so on, even though all these fit the label of Java web software. Similarly, it's important to understand clearly what kind of XSLT processing different products offer.

Complex Site Development

Neil Madden, an undergraduate at the University of Nottingham, has an XSLT system tuned for especially rapid deployment and maintenance. His scheme is organized around multisection sites, authored by teams of administrators, editors and users. He uses TclKit, an innovative open-source tool that combines database and HTTP functionality in a particularly lightweight, low-maintenance package. TclKit also knows how to interpret Tcl programs, so he wraps up tDOM with standard templates into a scriptable module. With this, he begins site-specific development:

  1. Design an XML document structure that captures the content of the site's data.

  2. Compose XSL stylesheets to transform data to meet each client's needs.

  3. Repeat steps one and two for each section that needs special requirements.

  4. Add users, sections and pages.

Scripted documents encapsulate these bundles of different kinds of data (site structure, XML sources, stylesheets) and make it easy to update and deploy a working site onto a new server or partition. Madden has plans to offer not just web-based editing but also a richer, quicker GUI interface. Tcl's uniformity and scriptability make this dual porting through either web service or local GUI practical.

Well-defined module boundaries are essential to the system. Designers maintain stylesheets, administrators manage privileges and editors assign sections without collision. With all of the functionality implemented as tiny scripts that glue together reliable components, it's easy to layer on new functionality. Madden's medium-term ambitions include a Wiki collaborative bulletin board, and XSP and FOP modules for generation of high-quality presentation output. Madden proudly compares his system to Cocoon, the well-known, Apache-based, Java-coded XML publishing framework. At a fraction of the cost in lines of code, his system bests Cocoon's performance by a wide margin.

Even further along in production use of tDOM XSLT is George J. Schlitz of MediaOne. He prepares financial documents with XSLT in a mission-critical web environment. While he originally began publication with Xalan, performance requirements drove him to switch to tDOM.

The fundamental point in all this is to be on the lookout for XML-coded or XML-codable data. Chat logs, legal transcripts, printer jobs, news photographs, screen layouts, genealogical records, game states, application designs, parcel shipments, medical files and much, much more are all candidates for XML-ization. Once in that format, XSLT processing is generally the most reliable and scalable way to render the data for specific uses.

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Re: XSLT Powers a New Wave of Web Applications

Anonymous's picture

While this article is an interesting introduction, I am very surprised that it would manage to not even mention libxslt which is probably one of the fastest, most reliable, and most frequently deployed processors, and AxKit which is similar to Cocoon in various ways, but less overdesigned and implemented within Apache using a powerful combination of C and Perl. Both are extremely succesful projects, with constantly growing user bases.

As for XSLT being more used by Tcl and Java folks than by Perl, Python, and C folks I think that's simply wrong, and is no more than an impression gathered from an incomplete sample.

Finally, as the author mentions benchmarks it would be nice to see them! I have no doubt that tDOM beats any pure Java XSLT processor flat, but what of the others? Beating libxslt (both for memory and for speed) appears to me to be a tough task. Even if tDOM were faster, I very much doubt it would be "twice as fast" as claimed rather boldly in this article.

Mod_xslt - ultimate XSLT engine for the web

Anonymous's picture

Check out http://freshmeat.net/projects/mod_xslt_ln/

and http://linuxnews.pl as an example of XML/XSLT technology.

With the mod_xslt you can for example pass the arguments to the XSLT programs.

Example of this is forum system on Linuxnews.pl

regards,

Pumpkin

mod_xobjex for Apache 1.3.x uses libxslt

Daniel Bibbens's picture

Similar to mod_xslt, mod_xobjex is a lighter, faster alternative that uses Daniel Veillard's libxslt (which is blazingly fast). With mod_xobjex, web applications are built with pure XSLT. mod_xobjex converts the HTTP Request into XML to which the requested XSL template is applied. Download it at xobjex.com.

XSLT, DOM, SQL and the web

Anonymous's picture

This paper may be of interest to those looking to publish data from relational databases on the net using XSLT.

Re: XSLT Powers a New Wave of Web Applications

Anonymous's picture

www.zvon.org hosts an excellent XSLT reference - a lot easier than reading the W3C documents :-)

If you just want to try out some XSLT examples, here's (http://www.julien-dubois.com) a server-side XSLT transformer, so that you don't need anything on your PC to get you started.

Re: XSLT Powers a New Wave of Web Applications

Anonymous's picture

The "How To Start XSLT Programming" link mentions the 0.63 code snap shot. The xslt engine in tDOM-0.7test is much improoved in XSLT compliance. Grab it from

http://sdf.lonestar.org/~loewerj/tdom.cgi

rolf ade

Re: XSLT Powers a New Wave of Web Applications

Anonymous's picture

And for those who want a fast and compliant XSLT
engine, use xsltproc available from the libxslt package on
most distributions. It is used by KDE and Gnome to generate
the HTML version of their DocBook docs.
Check the web page
and download area for further
informations, packages and the source !
Daniel Veillard

Re: XSLT Powers a New Wave of Web Applications

Anonymous's picture

Yes! Daniel Veillard's libraries and utilities are definitely the way to go for production-quality work with XSLT; they chew through huge groves with speed. It's a true open-source success and deserves more appreciation.

If you're interested in tracking XSLT's growth and maturation, check out the newest version of Michael Kay's SAXON - larger, slower, but also very cool.

Paul Ford

Re: XSLT Powers a New Wave of Web Applications

Anonymous's picture

The way I got started with XSLT was Sablotron; which is available here.. If you use perl, it is nice because it's a perl module; and it also has a command line vesion similar to the tcl command mentioned above. You don't need TCL though; just configure && make && make install.

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