Designing Your own XML Schema: Restrictions and User Defined Types - Restrictions based on patterns in XML Schema
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Let us consider that we would like to have an employee ID to be provided with only five digits, in the form of a string. If it is in the form of a string, it would accept any character. I wanted to restrict it to only digits. Another good example along the same lines would be a zip code.
In these situations, you can use “patterns” in XML Schema. Even though I present a simple example of this, I suggest you refer to http://www.w3c.org/ for further in-depth information on “patterns.” It is just beyond the scope of this article to concentrate so deeply on patterns.
Let us look at the following complete schema before I give a complete explanation:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/
XMLSchema" elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:element name="Employees">
<xs:annotation>
<xs:documentation>Contains All Employee information</xs:documentation>
</xs:annotation>
<xs:complexType>
<xs:sequence>
<xs:element name="Employee" maxOccurs="unbounded">
<xs:complexType>
<xs:sequence>
<xs:element name="ID">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{5}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="Name" type="xs:string" />
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<xs:key name="PK_Employee_ID">
<xs:selector xpath=".//Employee" />
<xs:field xpath="ID" />
</xs:key>
</xs:element>
</xs:schema>
You need to observe the following fragment within the above complete schema, which actually does the restriction:
<xs:element name="ID">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]{5}" />
</xs:restriction>
</xs:simpleType>
</xs:element>
The above “restriction” is of type “pattern” facet where it would allow any digit between zero and nine, and a maximum of five digits. And not only that, it would not accept less than five digits as well!
I strongly suggest you go through several types of patterns available in XML Schema criteria, before designing a schema. This will help you get a better grasp of what you need to know to design powerful schema.
Next: How to define your own simple type (user-defined data type) in XML Schema >>
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