Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

Load always works synchronously, so when it returns, you can be sure that the loadingstep has been completed. You will not get from Load any return value that denotes thefailure or the success of the operation. When something goes wrong with the Loadmethod, however, some exceptions are thrown. In particular, you will get aFileNotFoundException exception if you are pointing to a missing style sheet, and youwill get a more generic XsltCompileException exception if the XSLT script containserrors. An XsltCompileException exception provides you with a line position andnumber indicating where the error occurred in the style sheet.Loading the Style SheetThe input style sheet can be loaded from four sources: a URL, an XML reader, anXPath document, or an XPath navigator. Whatever the source, the Load method firstexpresses it as an XPath navigator. As discussed in Chapter 6, an XPath navigatorrepresents a generic interface able to navigate over any XMLbased, or XML-looking,data store. The XPathNavigator class enables you to move from one node to the nextand to retrieve node-sets using XPath queries.The source style sheet is normalized to an XPath navigator mostly for performancereasons. The style sheet must be compiled and, given the compiler's architecture, anavigator is an extremely efficient object for performing the task. Compiling is a processthat simply excerpts information from the original style sheet and stores it in handy datastructures for further use. The entire set of these data structures is said to be the stateof the XSLT processor. Figure 7-6 illustrates the flow of the Load method.Figure 7-6: The style sheet is first normalized to an XPath navigator and then compiled.Managing the Processor's StateThe style sheet compiler populates three internal data structures with the data readfrom the source. The compiled style sheet object shown in Figure 7-6 represents an255