You can also use XmlReader classes to determine various factors such as the depth of a node in an XML document, whether the node has attributes, the number of attributes in a node, and the value of an attribute. To perform validation while reading the XML data using the XmlReader class, use the new |
System.Xml.XmlReaderSettings class that exposes properties which can be set to appropriate values to validate XML data using DTD and XSD schemas. The XmlReaderSettings class is described in detail in Chapter 5. |
Although the .NET Framework includes concrete implementations of the XmlReader class, such as the |
XmlTextReader, XmlNodeReader, and the XmlValidatingReader classes, the recommended practice in .NET Framework 2.0 is to create XmlReader instances using the Create() method. The |
XmlReader object returned by the Create method has better conformance checking and compliance to the XML 1.0 recommendation. |
SAX Vs XmlReader |
When you first look at it, the .NET Framework class library’s implementation of forward-only access seems very similar to the Simple API for XML (SAX), but actually they are fundamentally different. Where SAX uses a more complex push model, the class library uses a simple pull model. This means that a developer requests or pulls data one record at a time instead of having to capture the data using event handlers. Coding using the .NET Framework class library’s implementation of forward-only access is more intuitive because you can handle the processing of an XML document as you would a simple file, using a good old-fashioned while loop. There is no need to learn about event handlers or SAX’s complex state machine. |
Random Access via DOM |
The XML DOM class, System.Xml.XmlDocument, is a representation of the XML document in memory. The .NET Framework DOM implementation provides classes that enable you to navigate through an XML document and obtain relevant information. Every XML document consists of parent and child nodes. The XmlDocument class has the capability to read in XML files, streams, or XmlReader objects. Among the many public methods of the XmlDocument class, you will want to start with the Load() |
method. Using this method, you can easily load XML data into an XmlDocument object. |
Choosing the Right XML Reader |
Basically, you could take an either/or approach when you choose your XML class for reading. For example, either you choose the XmlReader class for fast, forward-only, read-only, non-cached type reading. Or you can choose the DOM class XmlDocument for full-featured XML document reading and manipulation. The major deciding factors for choosing one method over the other are whether all data needs to be in memory at one time (large files take up large amounts of memory, which in many cases isn’t a good thing) and whether random access to the data is needed. When either of these factors is a requirement, the DOM tree should probably be used because the process of repeatedly reading forward sequentially through a docu- ment to find the right place in the stream of XML to read, update, or write random data is time consuming. |
Is XML API in .NET a Replacement for MSXML 6.0? |
Microsoft’s XML parser, MSXML 6.0 (now known as Microsoft XML Core Services), has historically provided much of the XML DOM support described in this section. The .NET XML managed objects largely overlap the functionality exposed in the COM-based MSXML 6.0 library. Generally, you want to use the managed objects offered in the various .NET XML namespaces. There are occasions, however, when you should use the MSXML 6.0 implementation when you need backward compatibility with |