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

Table 2-4: Types of Nodes in the XmlNodeType EnumerationNode TypeDescriptionSignificantWhitespace Represents a significant white space characterbetween markup text in a mixed-content model orwhite space within the scope ofxml:space="preserve".TextRepresents the text content of an element.WhitespaceRepresents an insignificant space between markuptext.XmlDeclaration Represents the XML declaration node.XmlDeclaration must be the first node in thedocument and can't have children. The node canhave attributes that provide version and encodinginformation.Table 2-4 includes all the possible types of nodes found within the body of an XMLdocument—at least when the document is parsed through a .NET XML reader. Noticethat the XML element that is normally perceived as being the node—that is, marked uptext—is said to be an element node. Attributes, comments, and even processinginstructions are just other types of nodes. In light of this, when you move from one nodeto the next, you are not necessarily moving between nodes of the same type.A lot of XML documents begin with several tags that do not represent any data content.The reader's MoveToContent method lets you skip all the heading information andposition the pointer directly in the first content node. In doing so, the method skips overthe following node types: ProcessingInstruction, DocumentType, Comment,Whitespace, and SignificantWhitespace.Specialized Reader ClassesThe XmlReader class defines only the clauses and appendices in the contract that.NET XML applications sign with the actual parser class. Because XmlReader is anabstract class, you'll use it in your code only as a reference type when type casting isneeded. In lieu of XmlReader, you can use any of its derived classes already defined inthe .NET Framework. In addition, you can use any other custom reader class that thirdpartyvendors, or you yourself, might have written. All of these reader classes share theprogramming interface with XmlReader, however, and provide an actual, albeit custom,implementation for each of the methods and properties listed in Table 2-1, on page 27,and Table 2-3, on page 30.Implementations of the XmlReader class extend the base class and vary in their designto support different scenarios. The .NET Framework supplies the following readerclasses:• XmlTextReader Extremely fast; the reader ensures that the XML sourceis well-formed but neither validates it against a schema or a DTD norresolves any embedded entity.• XmlValidatingReader An XML reader that can validate the source usinga DTD, an XML-Data Reduced (XDR) schema, and an XML SchemaDefinition (XSD). In addition, the reader is capable of expanding entitiesand also supports default attributes as defined in the DTD or schema.• XmlNodeReader The reader specializes in parsing XML data from anXML Document Object Model (XML DOM) subtree and does not supportvalidation.In the next section, we'll examine the XmlTextReader class—probably the mostfrequently used .NET reader class. Validating readers will be covered in Chapter 3;27