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1.5. Web Browser Support for XSLT

In a web application environment, performing XSLT transformations on the client instead of the server is valuable for a number of reasons. Most importantly, it reduces the workload on the server machine, allowing a greater number of clients to be served. Once a stylesheet is downloaded to the client, subsequent requests will presumably use a cached copy, therefore only the raw XML data will need to be transmitted with each request. This has the potential to greatly reduce bandwidth requirements.

Even more interesting tricks are possible when JavaScript is introduced into the equation. You can programmatically modify either the XML data or the XSLT stylesheet on the client side, reapply the stylesheet, and see the results immediately without requesting a new document from the server.

Microsoft introduced XSLT support into Version 5.0 of Internet Explorer, but the XSLT specification was not finalized at the time. Unfortunately, significant changes were made to XSLT before it was finally promoted to a W3C Recommendation, but IE had already shipped using the older version of the specification. Although Microsoft has done a good job updating its MSXML parser with full support for the final XSLT Recommendation, millions of users will probably stick to IE 5.0 or 5.5 for quite some time, making it very difficult to perform portable XSLT transformations on the client. For IE 5.0 or 5.5 users, the MSXML parser is available as a separate download from Microsoft. Once downloaded, installed, and configured using a separate program called xmlinst, the browser will be compliant with Version 1.0 of the XSLT recommendation. This is something that developers will want to do, but probably very few end users will have the technical skills to go through these steps.

At the time of this writing, Netscape had not introduced support for XSLT into its browsers. We hope this changes by the time this book is published. Although their implementation will be released much later than Microsoft's, it should be compliant with the latest XSLT Recommendation.

Yet another alternative is to utilize a browser plug-in that supports XSLT, although this approach is probably most effective within the confines of a corporation. In this environment, the browser can be controlled to a certain extent, allowing client-side transformations much sooner than possible on public web sites.

Because XSLT transformation on the client will likely be mired in browser compatibility issues for several years, the role of Java with respect to XSLT will continue to be important. One use will be to detect the browser using a Java servlet, and then deliver the appropriate stylesheet to the client only if a compliant browser is in use. Otherwise, the servlet will drive the transformation process by invoking the XSLT processor on the web server. Once we finish with XSLT syntax in the next two chapters, the role of Java and XSLT will be covered throughout the remainder of this book.



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