Re: Do Data Models Need to built on a Mathematical Concept?
Date: 4 May 2003 15:24:28 -0700
Message-ID: <4b45d3ad.0305041424.3a40c481_at_posting.google.com>
> A relation of degree n over the sets A1, A2, ..., An
> is simply any subset of the cartesian product A1xA2...xAn.
Ok, I can accept a well defined operation called cartesian product.
> For a binary relation the notation is usually R <included in> AxB
> where we call A the domain of R and B the codomain of R. So we say R is
> a binary relation from A to B. When A and B (the domain and codomain
> coincide) we call that a *binary relation over A*. So a binary relation
> R over A is simply a subset of the cartesian product AxA.
Your explanation and the three sited below from text books DO NOT accurately describe the fundamental form of a binary relation.
- A binary relation on A is a subset of (AxA).
- A set R is a binary relation if all elements of R are ordered pairs.
- Let A and B be sets. A binary relation from A to B is a subset of AxB.
These definitions involve multiple binary relations, but do not clearly define a binary relation. The fundamental form of a binary relation is two things that have something in common. Received on Mon May 05 2003 - 00:24:28 CEST