Primary and foreign keys in xml schema

Question

I am trying to insert primary and foreign keys in XSD schema file below :-

Primary key is StudentID and Foreign Keys are courseID, AddressID, GradeID.

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="Student">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="Title" type="xs:string"/>
      <xs:element name="FirstName" type="xs:string"/>
      <xs:element name="LastName" type="xs:string"/>
      <xs:element name="Dateborn"  type="xs:date"/>
      <xs:element name="Gender"  type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>
</xs:schema>

However above code is not working in my setup please help me in tracing the issue,

Answer 1

In general you would need to put more details in a question... So this should be enough to understand what else you might need to define, and how. I'll tackle what's needed to understand how to define a primary key/foreign key by illustrating an assumed student/address relationship.

First you need to define a context where these constraints hold true. In my modified XSD, I call it the "World".

<?xml version="1.0" encoding="utf-8" ?>
<!-- XML Schema generated by QTAssistant/XSD Module (http://www.paschidev.com) -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="World">
        <xs:complexType>
            <xs:sequence>
                <xs:element ref="Student" maxOccurs="unbounded"/>   
                <xs:element ref="Address" minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>          
        </xs:complexType>
        <xs:key name="PKStudents">
            <xs:selector xpath="Student/StudentID"/>
            <xs:field xpath="."/>
        </xs:key>
        <xs:key name="PKAddresses">
            <xs:selector xpath="Address/AddressID"/>
            <xs:field xpath="."/>
        </xs:key>
        <xs:keyref name="FKStudentToAddress" refer="PKAddresses">
            <xs:selector xpath="Student/AddressID"/>
            <xs:field xpath="."/>
        </xs:keyref>
    </xs:element>
    <xs:element name="Student">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="Title" type="xs:string"/>
                <xs:element name="FirstName" type="xs:string"/>
                <xs:element name="LastName" type="xs:string"/>
                <xs:element name="Dateborn" type="xs:date"/>
                <xs:element name="Gender" type="xs:string"/>
                <xs:element name="StudentID" type="xs:string"/>
                <xs:element name="AddressID" type="xs:string" minOccurs="0"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    <xs:element name="Address">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="AddressID" type="xs:string"/>
                <xs:element name="Street" type="xs:string"/>
                <xs:element name="City" type="xs:string"/>
                <xs:element name="Province" type="xs:string" minOccurs="0"/>
                <xs:element name="Country" type="xs:date" minOccurs="0"/>
                <xs:element name="PostalCode" type="xs:string" minOccurs="0"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

Then an XML like this would pass or fail, depending on what you do with the values in the StudentID and AddressID fields.

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<!-- Sample XML generated by QTAssistant (http://www.paschidev.com) -->
<World xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <Student>
        <Title>Title1</Title>
        <FirstName>FirstName1</FirstName>
        <LastName>LastName1</LastName>
        <Dateborn>1900-01-01</Dateborn>
        <Gender>Gender1</Gender>
        <StudentID>StudentID1</StudentID>
        <AddressID>AddressID1</AddressID>
    </Student>
    <Student>
        <Title>Title1</Title>
        <FirstName>FirstName1</FirstName>
        <LastName>LastName1</LastName>
        <Dateborn>1900-01-01</Dateborn>
        <Gender>Gender1</Gender>
        <StudentID>StudentID2</StudentID>
        <AddressID>AddressID1</AddressID>
    </Student>
    <Address>
        <AddressID>AddressID1</AddressID>
        <Street>Street1</Street>
        <City>City1</City>
        <Province>Province1</Province>
        <Country>1900-01-01</Country>
        <PostalCode>PostalCode1</PostalCode>
    </Address>
    <Address>
        <AddressID>AddressID2</AddressID>
        <Street>Street1</Street>
        <City>City1</City>
        <Province>Province1</Province>
        <Country>1900-01-01</Country>
        <PostalCode>PostalCode1</PostalCode>
    </Address>
</World>

To finish your solution, you would need to define the Course and Grade "entities" in your "world", define the xs:key for each, similar to Student/*Address*, then add CourseID and GradeID attributes to the entities that need them, and finally, define the keyref, as above, for Entity to Grade and Entity to Course.