Re: Comments on Norbert's topological extension of relational algebra

On 2015-12-19 11:14:52 +0000, Norbert_Paul said:

> R1
> object id1 id2
> --------------
> cube n 1
> cube n 2
> ...
> sausage m 1
> sausage m 2
> ...
> ball k 1
> ball k 2
> ..
>
> Then consider R1 a binary relation on PART:
> FOREIGN KEY(object id1) REFERENCES PART
> FOREIGN KEY(object id2) REFERENCES PART

The term "relation" is used to denote

1. a mathematical relation (the subset of a Cartesian product);
2. a named relation (a set of tuples);
3. an association defined by foreign keys.

Although it is clear from the context what you mean, calling R1 a "binary relation" (in the sense C) is a bit confusing because R1 is a relation of degree 3 (in the sense B). On the other hand, R1 represents a specialization preorder, which is a binary relation (in the sense A). In this specific example "binary relationship" or "binary association" might be a better term.

In general, I wish that we could use a less ambiguous terminology, especially to distinguish between A and B (but I am not fond of "relvar"...).

Nicola

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