[This is preliminary documentation and subject to change.]
Web-Based Enterprise Management (WBEM) supports singleton classes, or classes that can have only one instance. Because there is no need to uniquely identify one instance from another, singleton classes do not designate one or more of their properties as the key.
Singleton classes can be defined programmatically using the methods of the IWbemServices interface or with Managed Object Format (MOF) syntax. In either case, the Singleton standard qualifier is attached to the class declaration and set to the Boolean value of TRUE to designate the class as a singleton class. To ensure that the qualifier is propagated from the class to the instance, a qualifier flavor must also be included. The flag ToInstance is specified when defining the class using MOF; the constant WBEM_FLAVOR_FLAG_PROPAGATE_TO_INSTANCES when defining the class programmatically.
To retrieve an instance of a singleton class, call IWbemServices::GetObject with the bstrObjectPath parameter set to SingletonClassName="@".
For more information about defining classes with the MOF syntax, see Managed Object Format (MOF) Language.
For more information about qualifiers and qualifier flavors, see Qualifiers and Qualifier Flavors.