Methods on the XML type such as CREATESCHEMABASEDXML and ISSCHEMAVALID take an XSD (XML Schema Definition) schema as a parameter and validate the XML type instance against it. Teradata recommends that you store the schemas as XML type values in tables with unique identifiers associated with them. When invoking a method that requires the schema as an input argument, you can join the schema table and specify the schema by its unique identifier in the WHERE clause.