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Non-Deterministic Content Models
View an example of using an XML schema with a non-deterministic content model.
MikeRayMSFT
mikeray
randolphwest
05/05/2022
sql
xml
conceptual
non-deterministic content models
content models [XML in SQL Server]

Non-Deterministic content models

[!INCLUDE SQL Server Azure SQL Database]

Non-deterministic content models are accepted in [!INCLUDEssNoVersion] if the occurrence constraints are 0, 1, or unbounded.

Before [!INCLUDEssVersion2005] Service Pack 1 (SP1), [!INCLUDEssNoVersion] rejected XML schemas that had non-deterministic content models.

Example: Non-deterministic content model rejected

The following example attempts to create an XML schema with a non-deterministic content model. The code fails because it isn't clear whether the <root> element should have a sequence of two <a> elements or if the <root> element should have two sequences, each with an <a> element.

CREATE XML SCHEMA COLLECTION MyCollection AS '
<schema xmlns="http://www.w3.org/2001/XMLSchema">
    <element name="root">
        <complexType>
            <sequence minOccurs="1" maxOccurs="2">
                <element name="a" type="string" minOccurs="1" maxOccurs="2"/>
            </sequence>
        </complexType>
    </element>
</schema>
';
GO

The schema can be fixed by moving the occurrence constraint to a unique location. For example, the constraint can be moved to the containing sequence particle:

<sequence minOccurs="1" maxOccurs="4">
    <element name="a" type="string" minOccurs="1" maxOccurs="1"/>
</sequence>

Or the constraint can be moved to the contained element:

<sequence minOccurs="1" maxOccurs="1">
     <element name="a" type="string" minOccurs="1" maxOccurs="4"/>
</sequence>

Example: Non-deterministic content model accepted

The following schema would be rejected in versions of [!INCLUDEssNoVersion] before [!INCLUDEssVersion2005] SP1.

CREATE XML SCHEMA COLLECTION MyCollection AS '
<schema xmlns="http://www.w3.org/2001/XMLSchema">
    <element name="root">
        <complexType>
            <sequence minOccurs="0" maxOccurs="unbounded">
                <element name="a" type="string" minOccurs="0" maxOccurs="1"/>
                <element name="b" type="string" minOccurs="1" maxOccurs="unbounded"/>
            </sequence>
        </complexType>
    </element>
</schema>
';
GO

See also