XML

Designing Your own XML Schema: Constraining with Restrictions

This is second article in a series which guides you in designing XML Schemas right from the basics without any hurdles.

Author Info:

By: Jagadish Chaterjee

Poor Best

Rating:

/ 7

March 13, 2006

TABLE OF CONTENTS:

This topic is a bit more complicated than any of the previous sections, as it involves a bit of XPATH as well. What is a Primary Key? Anyone familiar with database design would understand it on the spot. A Primary Key is a special type of constraint (or restriction) which makes sure that all the values are unique and without nulls (you can forget about indexing in XML here).

For example, all the Employee IDs should never repeat and are compulsory. How do I enforce it? Let us look into the following complete schema, which does the same.

<?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" type="xs:string" />

<xs:element name="Name" type="xs:string" />

<xs:element name="Age" type="xs:int" />

</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>

Within the above code, you can see the definition of “Key.” I provided a name (“PK_Employee_ID”) to identify the key. I also specified that the element “ID” (in the “Employee” element) is the one which should be applicable to the “Key.” You can also provide more than one element as part of the “Key” (making it a composite primary key).

Any comments, suggestions, feedback, bugs, errors are highly appreciated at jag_chat@yahoo.com

DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware.