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Designing Your Own XML Schema: Indicators


This is the fourth (and last) in this series of articles, which guides you in designing XML Schemas right from the basics without any hurdles. This part explains what indicators are and how to use them.

Author Info:
By: Jagadish Chaterjee
Rating: 5 stars5 stars5 stars5 stars5 stars / 9
March 27, 2006
TABLE OF CONTENTS:
  1. · Designing Your Own XML Schema: Indicators
  2. · The Choice indicator in XML Schema
  3. · The Sequence indicator in XML Schema
  4. · The maxOccurs and minOccurs indicators in XML Schema
  5. · Groups in XML Schema
  6. · Attribute Groups in XML Schema

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Designing Your Own XML Schema: Indicators - The Choice indicator in XML Schema
(Page 2 of 6 )

Another indicator from the XML Schema vocabulary is the “Choice” indicator.  It is specially used to inform that one of the child elements could occur.  We can define as many numbers of elements as possible (with the “choice” indicator), but finally only one has to be chosen.  Let us consider the following schema:

<?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="EmployeeType">
                                         <xs:complexType>
                                               <xs:choice>
                                                            <xs:element name="Management" type="xs:string" />
                                                            <xs:element name="Clerk" type="xs:string" />
                                                      </xs:choice>
                                         </xs:complexType>
                                   </xs:element>
                             </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>

The most important fragment to concentrate on is the following:

<xs:element name="EmployeeType">
  <xs:complexType>
        <xs:choice>
              <xs:element name="Management" type="xs:string" />
              <xs:element name="Clerk" type="xs:string" />
        </xs:choice>
  </xs:complexType>
</xs:element>

The above specifies that the “EmployeeType” element can contain “Management” or “Clerk” elements (but not both).  A sample XML document, which conforms to the above schema, would be as follows:

<?xml version="1.0" encoding="UTF-8"?>
<Employees xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="C:\Documents and
Settings\Administrator\Desktop\Employees.xsd
">
      <Employee>
            <ID>1001</ID>
            <Name>Jag</Name>
            <EmployeeType>
                  <Management>Manager</Management>
            </EmployeeType>
      </Employee>
      <Employee>
            <ID>1002</ID>
            <Name>Chat</Name>
            <EmployeeType>
                  <Clerk>Admin</Clerk>
            </EmployeeType>
      </Employee>
</Employees>




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