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XML Schema Object Model Overview

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The Schema Object Model (SOM) in the Microsoft .NET Framework is a rich API that allows you to create, edit, and validate schemas programmatically. The SOM operates on XML schema documents similarly to the way the Document Object Model (DOM) operates on XML documents. XML schema documents are valid XML files that, once loaded into the SOM, convey meaning about the structure and validity of other XML documents which conform to the schema.

A schema is an XML document that defines a class of XML documents by specifying the structure or model of XML documents for a particular schema. A schema identifies the constraints on the content of the XML documents, and describes the vocabulary (rules or grammar) that compliant XML documents must follow in order to be considered schema-valid with that particular schema. Validation of an XML document is the process that ensures that the document conforms to the grammar specified by the schema.

The following are ways the SOM API in the .NET Framework enables you to create, edit, and validate schemas.

  • Load and save valid schemas to and from files.

  • Create in-memory schemas using strongly typed classes.

  • Interact with the XmlSchemaSet class to cache, compile, and retrieve schemas.

  • Interact with the Create method of the XmlReader class to validate XML instance documents against schemas.

  • Build editors for creating and maintaining schemas.

  • Dynamically edit a schema that can be complied and saved for use in the validation of XML instance documents.

The Schema Object Model

The SOM consists of an extensive set of classes in the System.Xml.Schema namespace corresponding to the elements in an XML schema. For example, the <xsd:schema>...</xsd:schema> element maps to the System.Xml.Schema.XmlSchema class, and all the information that can be contained within an <xsd:schema/> element can be represented using the XmlSchema class. Similarly, the <xsd:element>...</xsd:element> and <xsd:attribute>...</xsd:attribute> elements map to the System.Xml.Schema.XmlSchemaElement and System.Xml.Schema.XmlSchemaAttribute classes respectively. This mapping continues for all the elements of an XML schema creating an XML schema object model in the System.Xml.Schema namespace illustrated in the diagram that follows.

System.Xml.Schema Object Model

For more information about each class in the System.Xml.Schema namespace, see the System.Xml.Schema namespace reference documentation in the .NET Framework class library.

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