XSD Restrictions / Facets

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

Restrictions on Values

The following example defines an element named "age" with a restriction. The value of age cannot be lower than 0 or higher than 120:

<xs:element name="age">
<xs:simpleType>
    <xs:restriction base="xs:integer">
      <xs:minInclusive value="0"/>
      <xs:maxInclusive value="120"/>
    </xs:restriction>
</xs:simpleType>
</xs:element>

Restriction on a Set of Values

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

The following example defines an element named "car" with a restriction. The acceptable values are only: Audi, Golf, BMW:

<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 example above can also be written as:

<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 part of the "car" element.

Restriction on a Series of Values

To restrict the content of an XML element to a series of usable numbers or letters, we use the pattern constraint.

The following example defines an element named "letter" with a restriction. The acceptable values are only one of the lowercase letters a - z:

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

The next example defines an element named "initials" with a restriction. The acceptable values are three of the uppercase letters A - Z:

<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 next example also defines an element named "initials" with a restriction. The acceptable values are three of the uppercase or lowercase letters a - z:

<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 next example defines an element named "choice" with a restriction. The acceptable values are one of the letters x, y, or z:

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

The next example defines an element named "prodid" with a restriction. The acceptable values are a sequence of five Arabic digits, with each digit ranging from 0-9:

<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>

Other Restrictions on a Series of Values

The following example defines an element named "letter" with a restriction. The acceptable values are zero or more letters from a - z:

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

The following example defines an element named "letter" with a restriction. The acceptable values are one or more pairs of letters, each pair consisting of a lowercase letter followed by an uppercase letter. For example, "sToP" would pass validation of this pattern, but "Stop", "STOP", or "stop" would not pass validation:

<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 following example defines an element named "gender" with a restriction. The acceptable values are male or female:

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

The following example defines an element named "password" with a restriction. The acceptable values are a line of characters consisting of 8 characters, which must be uppercase or lowercase letters a - z or digits 0 - 9:

<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>

Restriction on Whitespace Characters

To specify how whitespace characters are handled, we need to use the whiteSpace restriction.

The following example defines an element named "address" with a restriction. This whiteSpace restriction is set to "preserve", which means the XML processor will not remove any whitespace characters:

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

This example also defines an element named "address" with a restriction. This whiteSpace restriction is set to "replace", which means the XML processor will remove all whitespace characters (line feeds, carriage returns, spaces, and tabs):

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

This example also defines an element named "address" with a restriction. This whiteSpace restriction is set to "collapse", which means the XML processor will remove all whitespace characters (line feeds, carriage returns, spaces, and tabs are replaced with spaces, leading and trailing spaces are removed, and multiple consecutive spaces are reduced to a single space):

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

Restrictions on Length

To restrict the length of a value in an element, we need to use the length, maxLength, and minLength restrictions.

This example defines an element named "password" with a restriction. Its value must be exactly 8 characters:

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

This example also defines an element named "password" with a restriction. Its value must be at least 5 characters and at most 8 characters:

<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>

Data Type Restrictions

Restriction	Description
enumeration	Defines a list of acceptable values
fractionDigits	Defines the maximum number of decimal places allowed. Must be greater than or equal to 0.
length	Defines the exact number of characters or list items allowed. Must be greater than or equal to 0.
maxExclusive	Defines the upper bound of a value. Allowed values must be less than this value.
maxInclusive	Defines the upper bound of a value. Allowed values must be less than or equal to this value.
maxLength	Defines the maximum number of characters or list items allowed. Must be greater than or equal to 0.
minExclusive	Defines the lower bound of a value. Allowed values must be greater than this value.
minInclusive	Defines the lower bound of a value. Allowed values must be greater than or equal to this value.
minLength	Defines the minimum number of characters or list items allowed. Must be greater than or equal to 0.
pattern	Defines the exact sequence of acceptable characters.
totalDigits	Defines the exact number of Arabic digits allowed. Must be greater than 0.
whiteSpace	Defines how whitespace characters (line feeds, carriage returns, spaces, and tabs) are handled.

Other Extensions