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

Other controls that the XmlTextWriter class performs on the generated XML outputensure that each document starts with the standard XML prolog, shown in the followingcode, and that any DOCTYPE node always precedes the document root node:This said, there is no absolute guarantee that users won't write badly formed code. Ifthe bad format can be detected, the writer throws an exception. Otherwise, the file isconsidered correctly written, but client applications might complain about it, as in Figure4-2.Figure 4-2: An XML file created with the XmlTextWriter class has a duplicated attribute thatthe class did not discover.The following code demonstrates how to write two identical attributes for a specifiednode:xmlw.WriteStartElement("element");xmlw.WriteAttributeString("value", s);xmlw.WriteAttributeString("value", s);xmlw.WriteEndElement();In the check made just before dumping data out, the writer neither verifies the namesand semantics of the attributes nor validates the schema of the resultant document,thus authorizing this code to generate bad XML.Building an XML DocumentUp to now, we've looked at several code snippets showing the XML text writer in action,but without going into details. Let's make up for this now. The necessary steps to createan XML document can be summarized as follows:• Initialize the document The output stream is already open, and at thisstage you simply write the XML prolog, including the XML 1.0 defaultdeclaration and any other heading information that the recommendationmandates to precede actual data nodes. (Typically, this informationconsists of processing instructions, schema references, and the DTD.)• Write data At this stage, you create XML nodes such as element nodes,attributes, CDATA and parsable text, entities, white space, and whatever121