Functions are special queries which have some input parameters and return exactly one object as result for one set of input parameters. Similar to builtin-queries, they are implemented by a PROLOG predicate which is defined either in the OB.builtin file (this file is part of every ConceptBase application) or in a LPI-file (see also section 5.2.2).
A couple of aggregation functions are predefined for counting, summing up, and computing the minimum/maximum/average. Furthermore, there are functions for arithmetic and string manipulation. See section E.2 for the complete list. Since functions are defined as regular Telos objects, you can load their definition on the Telos editor of the ConceptBase User Interface. This will also show you the precise parameter definition.
Unlike as for user-defined generic query classes, you have to provide fillers for all parameters of a function. We will refer to any query expression whose outer-most query is a function as a functional expression.