Deriving 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 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/.
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.
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.XML Schema Constraints and Relationships (ADO.NET)
Describes how relations are created implicitly when using XML Schema elements to create constraints in a DataSet.
Related Sections
- Using XML in a DataSet (ADO.NET)
Describes how to load and persist the relational structure and data in a DataSet as XML data.