With the module system it is possible to manage several knowledge bases, each of them containing a sequence of clauses and/or a context, where a context is a sequence of module names. The default module always is workspace. Before interpreting a goal, the module extension is created, which is a list of lists of all clauses of the prelude, the current module, and the context modules.
There is an analogy between the module system and the file system, exploited by the rich set of `m'-commands.
One can find an example dialog in appendix F.