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

XPath Expressions and XSLTIn the .NET Framework, XSLT and XPath expressions are fully supported but areimplemented in classes distinct from those that parse and write XML text. This is a keyfeature of the overall .NET XML API. Any functionality is provided through a smallhierarchy of objects, although each subtree connects and interoperates well withothers. Figure 1-2 demonstrates the interconnection between constituent APIs.Figure 1-2: The XMLDOM API is built on top of readers and writers, but both XSLT andXPath expressions need to have a complete and XMLDOM-based vision of the entire XMLdocument to process it.XML readers and writers are the primitive elements of the .NET XML API. WheneverXML text must be parsed or written, all classes, directly or indirectly, refer to them. Amore complex primitive element is the XMLDOM tree. Transformations and advancedqueries must rely on the document in its entirety being held in memory and accessiblethrough a well-known interface—the XMLDOM.The XSLT ProcessorThe key class for XSLT is XslTransform. The class works as an XSLT processor andcomplies with version 1.0 of the XSLT recommendation. The class has two keymethods, Load and Transform, whose behavior is for the most part selfexplanatory.Once you acquire an instance of the XslTransform class, you first load the source of anXSL document that contains the transformation rules. By calling the Transform method,you actually perform the conversion from native XML to the output format. Prior toapplying the transformation, the underlying XML document is loaded as a kind ofXMLDOM tree. (The details of XSLT are covered in Chapter 7.)18