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XmlSchemaCollection as a Schema Cache

The XmlSchemaCollection is a cache or library where XML-Data Reduced (XDR) and XML Schema definition language (XSD) schemas can be stored and validated. XmlSchemaCollection improves performance by caching schemas in memory instead of accessing them from a file or URL.

Note   Although the XmlSchemaCollection class stores both XDR schemas and XML Schemas, any method and property that takes or returns an XmlSchema object supports XML Schemas only.

Add Schemas to the Collection

Schemas are loaded to the collection using the Add method of XmlSchemaCollection, at which time the schema is associated with a namespace URI. For XML Schemas, the namespace URI will typically be the target namespace for the schema. For XDR schemas, the namespace URI is the namespace specified when the schema was added to the collection.

Check for a Schema in the Collection

You can check to see if a schema is in the collection by using the Contains method. The Contains method takes either an XmlSchema object (for XML Schemas only) or a string representing the namespace URI associated with the schema (for XML Schemas and XDR schemas).

Retrieve a Schema from the Collection

You can retrieve a schema from the collection by using the Item property. The Item property takes a string representing the namespace URI associated with the schema, typically its target namespace, and returns an XmlSchema object. The Item property applies to XML Schemas only. The return value is always a null reference for XDR schemas because they do not have an object model available.

Validate XML Documents Using XmlSchemaCollection

You can validate an XML instance document using an XmlSchemaCollection by creating the XmlSchemaCollection object, adding your schemas to the collection, and setting the Schemas property on the XmlValidatingReader to assign the created XmlSchemaCollection to the XmlValidatingReader.

Improved Performance

It is recommended, if you are validating more than one document against the same schema, that you use the XmlSchemaCollection because it provides better performance by caching schemas in memory.

The following code example creates the XmlSchemaCollection object, adds schemas to the collection, and sets the Schemas property.

Dim tr as XmlTextReader = new XmlTextReader("Books.xml")
Dim vr as XmlValidatingReader = new XmlValidatingReader(tr)
Dim xsc as XmlSchemaCollection = new XmlSchemaCollection
xsc.Add("urn:bookstore-schema", "Books.xsd")
XmlTextReader tr = new XmlTextReader("Books.xml");
XmlValidatingReader vr = new XmlValidatingReader(tr);
XmlSchemaCollection xsc = new XmlSchemaCollection();
xsc.Add("urn:bookstore-schema", "Books.xsd");  

See Also

Validation of XML with Schemas | XDR Validation with XmlSchemaCollection | XML Schema (XSD) Validation with XmlSchemaCollection