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XSD Restrictions/Facets

Restrictions are used to control acceptable values for XML elements or attributes. Restrictions on XML elements are called facets.

Restrictions on Values

This example defines an element called "age" with a restriction. The value of age can NOT be lower than 0 or greater than 100:

<xs:element name="age">

<xs:simpleType>
  <xs:restriction base="xs:integer">
    <xs:minInclusive value="0"/>
    <xs:maxInclusive value="100"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

Restrictions on a Set of Values

To limit the content of an XML element to a set of acceptable values, we would use the enumeration constraint.

This example defines an element called "car":

<xs:element name="car">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:enumeration value="Audi"/>
    <xs:enumeration value="Golf"/>
    <xs:enumeration value="BMW"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "car" element is a simple type with a restriction. The acceptable values are: Audi, Golf, BMW.

The example above could also have been written like this:.

<xs:element name="car" type="carType"/>

<xs:simpleType name="carType">
  <xs:restriction base="xs:string">
    <xs:enumeration value="Audi"/>
    <xs:enumeration value="Golf"/>
    <xs:enumeration value="BMW"/>
  </xs:restriction>
</xs:simpleType>

Note: In this case the type "carType" can be used by other elements because it is not a part of the "car" element.

Restrictions on a Series of Values

To limit the content of an XML element to define a series of numbers or letters that can be used, we would use the pattern constraint.

This example defines an element called "letter":

<xs:element name="letter">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="[a-z]"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "letter" element is a simple type with a restriction. The only acceptable value is ONE of the LOWERCASE letters from a to z.

The next example defines an element called "initials":

<xs:element name="initials">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="[A-Z][A-Z][A-Z]"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "initials" element is a simple type with a restriction. The only acceptable value is THREE of the UPPERCASE letters from a to z.

This example also defines an element called "initials":

<xs:element name="initials">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="[a-zA-Z][a-zA-Z][a-zA-Z]"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "initials" element is a simple type with a restriction. The only acceptable value is THREE of the LOWERCASE OR UPPERCASE letters from a to z.

This example defines an element called "choice":

<xs:element name="choice">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="[xyz]"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "choice" element is a simple type with a restriction. The only acceptable value is ONE of the following letters: x, y, OR z.

The next example defines an element called "prodid":

<xs:element name="prodid">

<xs:simpleType>
  <xs:restriction base="xs:integer">
    <xs:pattern value="[0-9][0-9][0-9][0-9][0-9]"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "prodid" element is a simple type with a restriction. The only acceptable value is FIVE digits in a sequence, and each digit must be in a range from 0 to 9.

Other Restrictions on a Series of Values

Some other restrictions that can be defined by the pattern constraint:

This example defines an element called "letter":

<xs:element name="letter">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="([a-z])*"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "letter" element is a simple type with a restriction. The acceptable value is zero or more occurrences of lowercase letters from a to z.

This example also defines an element called "letter":

<xs:element name="letter">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="([a-z][A-Z])+"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "letter" element is a simple type with a restriction. The acceptable value is one or more occurrences of a lowercase letter followed by a uppercase letter from a to z.

This example defines an element called "gender":

<xs:element name="gender">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="male|female"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "gender" element is a simple type with a restriction. The only acceptable values are male OR female.

This example defines an element called "password":

<xs:element name="password">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:pattern value="[a-zA-Z0-9]{8}"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "password" element is a simple type with a restriction. There must be exactly eight characters in a row and those characters must be lowercase or uppercase letters from a to z, or a number from 0 to 9.

Restrictions on White Space Characters

To specify how white space characters should be handled, we would use the whiteSpace constraint.

This example defines an element called "address":

<xs:element name="address">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:whiteSpace value="preserve"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "address" element is a simple type with a restriction. The whiteSpace constraint is set to "preserve", which means that the XML processor WILL NOT remove any white space characters.

This example also defines an element called "address":

<xs:element name="address">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:whiteSpace value="replace"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

This "address" element is a simple type with a restriction. The whiteSpace constraint is set to "replace", which means that the XML processor WILL REPLACE all white space characters (line feeds, tabs, spaces, and carriage returns) with spaces.

This example also defines an element called "address":

<xs:element name="address">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:whiteSpace value="collapse"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

This "address" element is a simple type with a restriction. The whiteSpace constraint is set to "collapse", which means that the XML processor WILL REMOVE all white space characters (line feeds, tabs, spaces, carriage returns are replaced with spaces, leading and trailing spaces are removed, multiple spaces are reduced to a single space).

Restrictions on Length

To limit the length of a value in an element, we would use the length, maxLength, and minLength constraints.

This example defines an element called "password":

<xs:element name="password">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:length value="8"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

The "password" element is a simple type with a restriction. The value must be exactly eight characters.

This example defines another element called "password":

<xs:element name="password">

<xs:simpleType>
  <xs:restriction base="xs:string">
    <xs:minLength value="5"/>
    <xs:maxLength value="8"/>
  </xs:restriction>
</xs:simpleType>

</xs:element> 

This "password" element is a simple type with a restriction. The value must be minimum five characters and maximum eight characters.

Restrictions for Datatypes

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