Convenient ways of specifying sets of data elements, implicitly by attributes (categories)
or explicitly by sets of names (classes).
- Categories are used for describing new data sets in assisting GUI
configuration. Classes are primarily for transferring groups of related
data elements.
- Categories are likely to be the naming system that users see and
understand. Classes are primarily of interest to the people running
servers.
- Both categories and classes are extensible by both the client and the server (new data
elements can be created within existing classes, new classes can be created, new
categories can be created, existing data elements can belong to new categories, etc.)
