The XmlDataDocument class is a derived class of the XmlDocument, and contains XML data. The advantage of the XmlDataDocument is that it provides a bridge between relational and hierarchical data. It is an XmlDocument that can be bound to a DataSet and both classes can synchronize changes made to data contained in the two classes. An XmlDocument that is bound to a DataSet allows XML to integrate with relational data, and you do not have to have your data represented as either XML or in a relational format. You can do both and not be constrained to a single representation of the data.
The benefits of having data available in two views are:
The structured portion of an XML document can be mapped to a dataset, and be efficiently stored, indexed, and searched.
Transformations, validation, and navigation can be done efficiently through a cursor model over the XML data that is stored relationally. At times, it can be done more efficiently against relational structures than if the XML is stored in an XmlDocument model.
The DataSet can store a portion of the XML. That is, you can use XPath or XslTransform to store to a DataSet only those elements and attributes of interest. From there, changes can be made to the smaller, filtered subset of data, with the changes propagating to the larger data in the XmlDataDocument.
You can also run a transform over data that was loaded into the DataSet from SQL Server. Another option is to bind .NET Framework classes-style-managed WinForm and WebForm controls to a DataSet that was populated from an XML input stream.
In addition to supporting XslTransform, an XmlDataDocument exposes relational data to XPath queries and validation. Basically, all XML services are available over relational data, and relational facilities, such as control binding, codegen, and so on, are available over a structured projection of XML without compromising XML fidelity.
Because XmlDataDocument is inherited from an XmlDocument, it provides an implementation of the W3C DOM. The fact that the XmlDataDocument is associated with, and stores a subset of its data within, a DataSet does not restrict or alter its use as an XmlDocument in any way. Code written to consume an XmlDocument works unaltered against an XmlDataDocument. The DataSet provides the relational view of the same data by defining tables, columns, relations, and constraints, and is a stand-alone, in-memory user data store.
The following illustration shows the different associations that XML data has with the DataSet and XmlDataDocument.
The illustration shows that XML data can be loaded directly into a DataSet, which allows direct manipulation with XML in the relational manner. Or, the XML can be loaded into a derived class of the DOM, which is the XmlDataDocument, and subsequently loaded and synchronized with the DataSet. Because the DataSet and XmlDataDocument are synchronized over a single set of data, changes made to the data in one store are reflected in the other store.
The XmlDataDocument inherits all the editing and navigational features from the XmlDocument. There are times when using the XmlDataDocument and its inherited features, synchronized with a DataSet, is a more appropriate option than loading XML directly into the DataSet. The following table shows the items to be considered when choosing which method to use to load the DataSet.
|When to load XML directly into a DataSet||When to synchronize an XmlDataDocument with a DataSet|
|Queries of data in the DataSet are easier using SQL than XPath.||XPath queries are needed over data in the DataSet.|
|Preservation of element ordering in the source XML is not critical.||Preservation of element ordering in the source XML is critical.|
|White space between elements and formatting does not need to be preserved in the source XML.||White space and formatting preservation in the source XML is critical.|
If loading the DataSet from an XmlDataDocument addresses your needs, see Synchronizing a Datasetwith an XML Document.