Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

For an effective programmatic manipulation of an XML schema, you need an objectmodel. An object model enables you to build and edit schema information in memory. Italso gives you access to each element that forms the schema and that exposesread/write properties in homage to the pre-schema-validation and post-schemavalidationinfoset specifications.The .NET Framework provides a hierarchy of classes under the System.Xml.Schemanamespace to edit existing schemas or create new ones from the ground up. The rootclass of the hierarchy is XmlSchema. Once your application holds an instance of theclass, it can load an existing XSD file and populate the internal properties andcollections with the contained information. By using the XmlSchema programminginterface, you can then add or edit elements, attributes, and other schema components.Finally, the class exposes a Write method that allows you to persist to a valid streamobject the current contents of the schema.Reading a Schema from a FileYou can create an instance of the XmlSchema class in two ways. You can use thedefault constructor, which returns a new, empty instance of the class, or you can usethe static Read method.The Read method operates on schema information available through a stream, a textreader, or an XML reader. The schema returned is not yet compiled. The Read methodaccepts a second argument—a validation event handler such as the ones discussed inthe section "The XmlValidatingReader Programming Interface," on page 78. You canset this argument to null, but in this case you won't be able to catch and handlevalidation errors. The following code shows how to read and compile a schema usingthe .NET SOM:XmlSchema schema;XmlTextReader reader = new XmlTextReader(filename);schema = XmlSchema.Read(reader, null);schema.Compile(null);//// Do something here//⋮reader.Close();Once the schema has been compiled, you can access the constituent elements of theschema as defined by the PSVI. To access the actual types in the schema, you use theSchemaTypes collection. One of the differences between the information availablebefore and after compilation is that an included complex type will not be detected untilthe schema is compiled. For example, in eu_address.xsd, we extended theAddressType type after importing it through the tag. To programmaticallydetect the presence of the AddressType complex type, however, you must first compilethe schema, which would expand the include element that imports the type definition.The following code snippet demonstrates how to get the list of complex types defined inthe specified schema after compilation:void ListComplexTypes(string filename){XmlSchema schema;99