[SCL] Functional dependencies

[John F. Sowa]

Folks,

I am currently writing the mapping from CGIF to CL
semantics, and one of the CG constructs that we have
been using is called an actor, which is defined to
have two disjoint kinds of arcs:  input arcs and
output arcs.

An actor with exactly one output arc is called
a function, but in general, actors are relations
that may have more than one output.

Question:  I'd like to ask whether anyone else finds
this useful and worth putting into CL?  I can define
the notion in CGs independently of whether it is
explicitly recognized in CL, but I would like to know
whether other people might consider it useful.

Following are two definitions that I am putting into
Annex B of the CL document.  The notion of functional
dependency is widely used in database theory, where the
set of input arcs corresponds to the _key_ of a relation,
which uniquely determines all the other values.

John
_____________________________________________________

actor.

A conceptual relation in which functional dependencies are explicitly 
indicated. Formally, the arcs of any actor are explicitly marked as the 
disjoint union of a set of input arcs and output arcs, and every output 
arc is functionally dependent on some subset of the input arcs. An actor 
that has exactly one output arc is called a function.

functional dependency.

A property of some type t of conceptual relation. Formally, an arc a of 
a conceptual relation r of type t is said to be functionally dependent 
on some subset of one or more arcs S={a1,...,an} of r where a is not in 
S, provided that the following condition is true:

    For any possible sequence of entities e1,...,en that may occur
    as referents of concepts linked to the arcs a1,...,an respectively,
    there exists one and only one entity e that may occur as the referent
    of the concept linked to arc a.

If this condition is true, the relation r is said to have a functional 
dependency of arc a on the arcs in S.

Source:

    http://www.jfsowa.com/cg/annexb.htm
    Conceptual Graph Interchange Format