Represents an operation on catalogue(s).

An instance of this interface performs an operation on one or more catalogues and stores intermediate and final results of the operation.

The first catalogue in its argument(s) is called the 'source catalogue' or 'source' and the following results are stored:

Messages: also called 'all', are valid messages for the given domain after the operation is performed.

New Messages: also called 'new' (new = all ∖ source = {x: x ∈ all ∧ x ∉ source}).

Obsolete Messages: also called 'obsolete' (obsolete = source ∖ all = {x: x ∈ source ∧ x ∉ all}).

Result: also called 'result', is the resulting catalogue for the given domain that holds the same messages as 'all'.