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Wildcard Components and Content Validation

Wildcard components are used to increase flexibility in what is allowed to appear in a content model. These components are supported in the XSD language in the following ways:

  • Element wildcard components. These are represented by the <xsd:any> element.

  • Attribute wildcard components. These are represented by the <xsd:anyAttribute> element.

Both wildcard character elements, <xsd:any> and <xsd:anyAttribute>, support the use of a processContents attribute. This lets you specify a value that indicates how XML applications handle the validation of document content associated with these wildcard character elements. These are the different values and their effect:

  • The strict value specifies that the contents are fully validated.

  • The skip value specifies that the contents are not validated.

  • The lax value specifies that only elements and attributes for which schema definitions are available are validated.

The XML Schema specification uses lax validation for elements of the anyType type. Because SQL Server 2005 did not support lax validation, strict validation was applied for elements of the anyType. Beginning with SQL Server 2008, lax validation is supported. Content of elements of type anyType will be validated using lax validation.

The following example illustrates the lax validation. The schema element e is of the anyType type. The example creates typed xml variables and illustrates the lax validation of the element of the anyType type.

CREATE XML SCHEMA COLLECTION SC AS '
<schema xmlns="http://www.w3.org/2001/XMLSchema" 
        targetNamespace="http://ns">
   <element name="e" type="anyType"/>
   <element name="a" type="byte"/>
   <element name="b" type="string"/>
 </schema>'
GO

The following example succeeds, because the validation of <e> is successful:

DECLARE @var XML(SC)
SET @var = '<e xmlns="http://ns"><a>1</a><b>data</b></e>'
GO

The following example succeeds. The instance is accepted, even though no element <c> is defined in the schema:

DECLARE @var XML(SC)
SET @var = '<e xmlns="http://ns"><a>1</a><c>Wrong</c><b>data</b></e>'
GO

The XML instance in the following example is rejected, because the definition of the <a> element does not allow a string value.

DECLARE @var XML(SC)
SET @var = '<e xmlns="http://ns"><a>Wrong</a><b>data</b></e>'
SELECT @var
GO

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