An attribute class is a container object that groups related attributes. The attributes of an object type are organized into one or more attribute classes. For example, within the System Resource object type there is a Processor attribute class and a BIOS attribute class. Within the Processor attribute class there are attributes such as Device ID, Manufacturer, Resource ID, and so on. The attribute classes from which you can select include all the attribute classes belonging to the object type for the current query. Attribute classes are directly analogous to SQL tables and WBEM classes.
An attribute is the specific property that the query searches for. Attributes must be members of an attribute class that is associated with the object type of the current query. Attributes are directly analogous to SQL table columns and WBEM properties.
About Query Elements
About Object Types
Using Queries to Locate Resources Overview