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

XMLDOM model (memory footprint and bandwidth required to process largedocuments) are structural and stem directly from design choices.SAX parsers work by letting client applications pass living instances of platform-specificobjects to handle parser events. The parser controls the whole process and pushesdata to the application, which is in turn free to accept or simply ignore the data. TheSAX model is extremely lean and features a limited complexity in space.The .NET Framework provides full support for the XMLDOM parsing model but not forthe SAX model. The set of .NET Framework XML core classes supports two parsermodels: XMLDOM and a new model called an XML reader. The lack of support for SAXparsers does not mean that you have to renounce the functionality that a SAX parsercan bring, however. All the functions of a SAX parser can be easily and even moreeffectively implemented using an XML reader. Unlike a SAX parser, a .NET FrameworkXML reader works under the total control of the client application, enabling theapplication to pull out only the data it really needs and skip over the remainder of theXML stream.Readers are based on .NET Framework streams and work in much the same way as adatabase cursor. Interestingly, the classes that implement this cursor-like parsing modelalso provide the substrate for the .NET Framework implementation of the XMLDOMparser. Two abstract classes—XmlReader and XmlWriter—are at the very foundation ofall .NET Framework XML classes, including XMLDOM classes, ADO.NET-relatedclasses, and configuration classes. So in the .NET Framework you have two possibleapproaches when it comes to processing XML data. You can use either any classesdirectly built onto XmlReader and XmlWriter or classes that expose information throughthe well-known XMLDOM.The set of XML core classes also includes tailor-made class hierarchies to supportother related XML technologies such as XSLT, XPath expressions, and the SchemaObject Model (SOM).We'll look at XML core classes and related standards in the following chapters. Inparticular, Chapter 2, Chapter 3, Chapter 4, and Chapter 5 describe the core classesand parsing models. Chapter 6 and Chapter 7 examine the related standards, such asXPath and XSL.XML and ADO.NETThe interaction between ADO.NET classes and XML documents takes one of twoforms:• Serialization of ADO.NET objects (in particular, the DataSet object) toXML documents and corresponding deserialization. Data can be saved toXML in a variety of formats, with or without schema information, as a fullsnapshot of the in-memory data including pending changes and errors, orwith just the current instance of the data.• A dual-access model that lets you access and update the same piece ofdata either through a hierarchical programming interface or using theADO.NET relational API. Basically, you can transform a DataSet objectinto an XMLDOM object and view the XMLDOM's subtrees as tablesmerged with the DataSet object's tables.The ADO.NET DataSet class represents the only .NET Framework object that can benatively saved to XML. The XML representation of a DataSet object can have twodifferent layouts: the ADO.NET normal form and the DiffGram format. In particular, theDiffGram format describes the history of the data and all recent changes. Eachchanged row in each table is represented by two nodes: the first node contains the9