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

denote insertions, deletions, and updates. The mapping schema of the XML viewcontains the necessary information to map XML elements and attributes to tables andcolumns in the database. From a .NET Framework perspective, Updategrams look a lotlike DiffGrams. In SQL Server 2000, however, Updategrams are the native XMLlanguage to denote database changes.The OPENXML Rowset ProviderOPENXML is a T-SQL function that takes care of inserting data represented as an XMLdocument. OPENXML parses the contents of the XML document and exposes it as arowset. As a result, the records in the rowset can be stored in database tables.OPENXML is not a write-only keyword that you can use only with INSERT or UPDATE.Because it is a generic rowset provider, you can use it with statements such asSELECT and SELECT INTO, and in general wherever a source table or view isaccepted.OPENXML takes up to three arguments, as shown here:OPENXML (handle, rowpattern [, flags])[WITH (SchemaDeclaration | TableName)]The first argument (handle) is the handle of the internal representation of an XMLdocument. The document handle is created by the sp_xml_preparedocument systemstored procedure. The rowpattern argument is the XPath expression that selects thenodes in the source XML that must be processed as database rows.The flags argument is optional and, if specified, indicates how attributes and elementsin the selected nodes should be processed. By default, the flag is set to 1, whichindicates attribute-centric mapping. Attribute-centric mapping accepts input values onlyfrom the attributes of the selected nodes. The mapping between attributes and columnsis determined by name. Alternatively, you can specify element-centric mapping(a valueof 2). Element-centric mapping is similar to attribute-centric mapping except for the factthat it accepts input values from the text of child element nodes.Caution You could also opt for mixed mapping—a value of 3—bycombining attribute-centric and element-centric mapping. In thiscase, attribute-centric mapping is applied first, and then for allstill unmatched columns, an element-centric mapping is applied.You should use this feature only when absolutely necessary.Using a double flag can significantly slow performance.The WITH clause is optional and can be used to define the schema of the target table.If a table with the desired schema already exists, you simply indicate the table name.This is what commonly happens when you use OPENXML to write data. When you useOPENXML with a SELECT statement, you can specify the schema of the columnsbeing returned. (More details on the syntax of OPENXML can be found in SQL Server2000 Books Online.)OPENXML in ActionThe first step in using OPENXML is calling the sp_xml_preparedocument storedprocedure to parse the XML document. The stored procedure returns a treerepresentation of the nodes in the XML document, and this in-memory image becomesthe input for OPENXML. The stored procedure returns the handle of the document asan output parameter. Here's an example of how to use OPENXML:DECLARE @handle intEXEC sp_xml_preparedocument @handle OUTPUT,N'306