Retrieving Class Definitions
Schema queries are WQL statements that request class definitions and information about schema associations. Class providers use schema queries in their instances of the __ClassProviderRegistration class to specify the classes that they support when they register with WMI. Schema queries are placed in the ResultSetQueries, ReferencedSetQueries, and UnsupportedQueries properties of the __ClassProviderRegistration instance.
Schema queries are similar to data queries in that they support the following WQL statements:
A schema query is similar to a REFERENCES OF data query that specifies the ClassDefsOnly keyword; in other words, that returns a result set of class definition objects rather than actual instances of association classes. However, REFERENCES OF returns class definitions only if there are instances present. A schema query returns class definitions whether or not instances are present.