IBM Version 5 manual XML applications

3.1 XML applications

Today’s organizations’ rapid movement towards e-business brings new demands on defining flexible systems architectures. Systems need to be powerful, scalable, robust, and most of all, capable of meeting new business requirements. With that in mind, applications often need to be able to support multiple client types, all with different capabilities. The dominant client type for Web applications is currently the desktop browser, but that will not last forever. Pervasive Computing is rapidly evolving, introducing the use of cellular phones, PDAs, and other front-end devices, all with different XML capabilities. So as time passes by, each application gets a much broader audience, using a variety of new devices for sending and receiving information.

The most recent edition of any browser that might have XML support cannot be a prerequisite for using an XML based application. We also do not want to send the same XML document to every client, because some users of the application might be authorized to see more data than others. We must have the ability to process XML documents and generate the kind of response to the client that is adequate for the client type.

Extensible Stylesheet Language Transformations (XSLT) is designed to transform XML data into some other XML form. An XSLT processor, such as Apache’s Xalan, performs transformations using one or more XSLT stylesheets, which are also XML documents. Typically, in an XSLT- and Java-based Web application, XML data is generated dynamically based on database queries. Although some databases can export data directly as XML, you will often write custom Java code to extract data using JDBC and convert it into XML. In order to display this XML data on most browsers, it must first be converted into HTML. The XML data is fed into the processor as one input, and as XSLT stylesheet is provided as a second input. The output is then sent directly to the Web browser as a stream of HTML. The XSLT stylesheet produces HTML formatting instructions, while the XML provides raw data.

So in conclusion, at the heart of every XML application is an XML Processor that parses an XML document, so that the document elements can be retrieved and transformed into a presentation understood by the target client. The other responsibility of the parser is to check the syntax and structure of the XML document. The focus of this chapter is on the Xalan Java processor with all the aspects involved in processing an XML document.

56 The XML Files: Development of XML/XSL Applications Using WebSphere Studio