Re: Issues with the logical consistency of The Third Manifesto
Date: 15 Nov 2004 12:06:20 -0800
Message-ID: <1b604f4e.0411151206.146b57f3_at_posting.google.com>
Jonathan Leffler <jleffler_at_earthlink.net> wrote in message news:<4196FB0A.4030902_at_earthlink.net>...
> Q1: "relation values are manipulated by [...] operators defined
> specifically for their types"?
>
> A1: No, relations are manipulated by generic operators, not by
> operators defined for a specific relation. That is, the JOIN operator
> is not tied to a single pair of relations. The JOIN operator in TTM
> works on any pair of relations (subject only fixing up name/type
> clashes in the attributes via the RENAME operator). That is *not* an
> operation defined specifically for any particular pair of relations.
>
But isn't JOIN a mapping from relations to relations? Regardless of
the most specific "type" of relation? (After all its still a
relation.) Taken with the other relational operators, haven't we
defined an algebra over a type? The type being the relation?
Abstractly, if we can take a "type" without regard to its structure, we can define an algebra over that type. From that 30,000 ft view, relations and objects have a lot of similarities. At least that's what it sounds like to me. Received on Mon Nov 15 2004 - 21:06:20 CET