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sp_xml_preparedocument (Transact-SQL)

Updated: 14 April 2006

Reads the XML text provided as input, parses the text by using the MSXML parser (Msxmlsql.dll), and provides the parsed document in a state ready for consumption. This parsed document is a tree representation of the various nodes in the XML document: elements, attributes, text, comments, and so on.

sp_xml_preparedocument returns a handle that can be used to access the newly created internal representation of the XML document. This handle is valid for the duration of the session or until the handle is invalidated by executing sp_xml_removedocument.

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A parsed document is stored in the internal cache of SQL Server 2005. The MSXML parser uses one-eighth the total memory available for SQL Server. To avoid running out of memory, run sp_xml_removedocument to free up the memory.

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For backwards compatibility, sp_xml_preparedocument collapses the CR (char(13)) and LF (char(10)) characters in attributes even if these characters are entitized.

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The XML parser invoked by sp_xml_preparedocument can parse internal DTDs and entity declarations. Because maliciously constructed DTDs and entity declarations can be used to perform a denial of service attack, we strongly recommend that users not directly pass XML documents from untrusted sources to sp_xml_preparedocument.

To mitigate recursive entity expansion attacks, sp_xml_preparedocument limits to 10,000 the number of entities that can be expanded underneath a single entity at the top level of a document. The limit does not apply to character or numeric entities. This limit allows documents with many entity references to be stored, but prevents any one entity from being recursively expanded in a chain longer than 10,000 expansions.

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sp_xml_preparedocument limits the number of elements that can be open at one time to 256.

Topic link icon Transact-SQL Syntax Conventions


sp_xml_preparedocument
hdoc 
OUTPUT
[ , xmltext ]
[ , xpath_namespaces ] 

hdoc

Is the handle to the newly created document. hdoc is an integer.

[ xmltext ]

Is the original XML document. The MSXML parser parses this XML document. xmltext is a text parameter: char, nchar, varchar, nvarchar, text, ntext or xml. The default value is NULL, in which case an internal representation of an empty XML document is created.

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sp_xml_preparedocument can only process text or untyped XML. If an instance value to be used as input is already typed XML, first cast it to a new untyped XML instance or as a string and then pass that value as input. For more information, see Typed vs. Untyped XML.

[ xpath_namespaces ]

Specifies the namespace declarations that are used in row and column XPath expressions in OPENXML. xpath_namespaces is a text parameter: char, nchar, varchar, nvarchar, text, ntext or xml.

The default value is <root xmlns:mp="urn:schemas-microsoft-com:xml-metaprop">. xpath_namespaces provides the namespace URIs for the prefixes used in the XPath expressions in OPENXML by means of a well-formed XML document. xpath_namespaces declares the prefix that must be used to refer to the namespace urn:schemas-microsoft-com:xml-metaprop; this provides metadata about the parsed XML elements. Although you can redefine the namespace prefix for the metaproperty namespace by using this technique, this namespace is not lost. The prefix mp is still valid for urn:schemas-microsoft-com:xml-metaprop even if xpath_namespaces contains no such declaration.

0 (success) or >0 (failure)

Requires membership in the public role.

A. Preparing an internal representation for a well-formed XML document

The following example returns a handle to the newly created internal representation of the XML document that is provided as input. In the call to sp_xml_preparedocument, a default namespace prefix mapping is used.

DECLARE @hdoc int
DECLARE @doc varchar(1000)
SET @doc ='
<ROOT>
<Customer CustomerID="VINET" ContactName="Paul Henriot">
   <Order CustomerID="VINET" EmployeeID="5" OrderDate="1996-07-04T00:00:00">
      <OrderDetail OrderID="10248" ProductID="11" Quantity="12"/>
      <OrderDetail OrderID="10248" ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" ContactName="Carlos Gonzlez">
   <Order CustomerID="LILAS" EmployeeID="3" OrderDate="1996-08-16T00:00:00">
      <OrderDetail OrderID="10283" ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
--Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @hdoc OUTPUT, @doc
-- Remove the internal representation.
exec sp_xml_removedocument @hdoc

B. Preparing an internal representation for a well-formed XML document with a DTD

The following example returns a handle to the newly created internal representation of the XML document that is provided as input. The stored procedure validates the document loaded against the DTD included in the document. In the call to sp_xml_preparedocument, a default namespace prefix mapping is used.

DECLARE @hdoc int
DECLARE @doc varchar(2000)
SET @doc = '
<?xml version="1.0" encoding="UTF-8" ?> 
<!DOCTYPE root 
[<!ELEMENT root (Customers)*>
<!ELEMENT Customers EMPTY>
<!ATTLIST Customers CustomerID CDATA #IMPLIED ContactName CDATA #IMPLIED>]>
<root>
<Customers CustomerID="ALFKI" ContactName="Maria Anders"/>
</root>'

EXEC sp_xml_preparedocument @hdoc OUTPUT, @doc

C. Specifying a namespace URI

The following example returns a handle to the newly created internal representation of the XML document that is provided as input. The call to sp_xml_preparedocument preserves the mp prefix to the metaproperty namespace mapping and adds the xyz mapping prefix to the namespace urn:MyNamespace.

DECLARE @hdoc int
DECLARE @doc varchar(1000)
SET @doc ='
<ROOT>
<Customer CustomerID="VINET" ContactName="Paul Henriot">
   <Order CustomerID="VINET" EmployeeID="5" 
           OrderDate="1996-07-04T00:00:00">
      <OrderDetail OrderID="10248" ProductID="11" Quantity="12"/>
      <OrderDetail OrderID="10248" ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" ContactName="Carlos Gonzlez">
   <Order CustomerID="LILAS" EmployeeID="3" 
           OrderDate="1996-08-16T00:00:00">
      <OrderDetail OrderID="10283" ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
--Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @hdoc OUTPUT, @doc, '<ROOT xmlns:xyz="urn:MyNamespace"/>'

Release History

14 April 2006

New content:
  • Described the new entity expansion limit introduced in Service Pack 1.
  • Described the new element limit introduced in Service Pack 1.

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