Generating DataSet Relational Structure from XML Schema (XSD)

This section provides an overview of how the relational schema of a DataSet is built from an XML Schema definition language (XSD) schema document. In general, for each complexType child element of a schema element, a table is generated in the DataSet. The table structure is determined by the definition of the complex type. Tables are created in the DataSet for top-level elements in the schema. However, a table is only created for a top-level complexType element when the complexType element is nested inside another complexType element, in which case the nested complexType element is mapped to a DataTable within the DataSet.

For more information about the XML Schema definition language (XSD), see the World Wide Web Consortium (W3C) XML Schema Part 0: Primer Recommendation, the XML Schema Part 1: Structures Recommendation, and the XML Schema Part 2: Datatypes Recommendation, located at http://www.w3.org/TR/.

The following example demonstrates an XML Schema where customers is the child element of the MyDataSet element, which is a DataSet element.

 <xs:schema id="SomeID" 
              
             xmlns:xs="http://www.w3.org/2001/XMLSchema" 
             xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
    <xs:element name="MyDataSet" msdata:IsDataSet="true">
      <xs:complexType>
        <xs:choice maxOccurs="unbounded">
          <xs:element name="customers" > 
            <xs:complexType >
              <xs:sequence>
                <xs:element name="CustomerID" type="xs:integer" 
                             minOccurs="0" />
                <xs:element name="CompanyName" type="xs:string" 
                             minOccurs="0" />
                <xs:element name="Phone" type="xs:string" />
              </xs:sequence>
            </xs:complexType>
           </xs:element>
        </xs:choice>
      </xs:complexType>
    </xs:element>
  </xs:schema>

In the preceding example, the element customers is a complex type element. Therefore, the complex type definition is parsed and the mapping process creates the following table.

Customers (CustomerID , CompanyName, Phone)

The data type of each column in the table is derived from the XML Schema type of the corresponding element or attribute specified. For a list of XML Schema data types and their corresponding .NET Framework data types, see Data Type Support between XML Schema (XSD) Types and .NET Framework Types.

Note   If the element

customers

is of a simple XML Schema data type such as integer, no table is generated. Tables are only created for the top-level elements that are complex types.

In the following XML Schema, the Schema element has two element children, InStateCustomers and OutOfStateCustomers.

 <xs:schema id="SomeID" 
              
             xmlns:xs="http://www.w3.org/2001/XMLSchema" 
             xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
    <xs:element name="InStateCustomers" type="customerType" />
    <xs:element name="OutOfStateCustomers" type="customerType" />
     <xs:complexType name="customerType" >
         ...
      </xs:complexType>

    <xs:element name="MyDataSet" msdata:IsDataSet="true">
      <xs:complexType>
        <xs:choice maxOccurs="unbounded">
          <xs:element ref="customers" />
        </xs:choice>
      </xs:complexType>
    </xs:element>
  </xs:schema>

Both the InStateCustomers and the OutOfStateCustomers child elements are complex type elements (customerType). Therefore, the mapping process generates the following two identical tables in the DataSet.

InStateCustomers (CustomerID , CompanyName, Phone)
OutOfStateCustomers (CustomerID , CompanyName, Phone)

In This Section

• Mapping XML Schema (XSD) Constraints to DataSet Constraints
  Describes the XML Schema elements used to create unique and foreign key constraints in a DataSet.
• Generating DataSet Relations from XML Schema (XSD)
  Describes the XML Schema elements used to create relations between table columns in a DataSet.
• Understanding the Interrelationship between Constraints and Relationships
  Describes how relations are created implicitly when using XML Schema elements to create constraints in a DataSet.

Related Sections

• XML and the DataSet
  Describes how to load and persist the relational structure and data in a DataSet as XML data.
• XML Schema Reference (XSD)
  Provides a reference of the XML Schema definition language (XSD).