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title description author ms.author ms.reviewer ms.date ms.service ms.subservice ms.topic helpviewer_keywords
Wildcard Components and Content Validation
Learn how the XML Element and Attribute wildcard components are used to increase flexibility in what is allowed to appear in a content model.
MikeRayMSFT
mikeray
randolphwest
05/05/2022
sql
xml
conceptual
wildcard components [XML]
content validation [XML]

Wildcard components and content validation

[!INCLUDE SQL Server Azure SQL Database]

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 aren't validated.

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

Lax validation and xs:anyType elements

The XML Schema specification uses lax validation for elements of the anyType type. Because [!INCLUDEssVersion2005] didn't support lax validation, strict validation was applied for elements of the anyType. Beginning with [!INCLUDEsql2008-md], 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 doesn't allow a string value.

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

See also