Re: no names allowed, we serve types only
Date: Tue, 16 Feb 2010 01:47:42 -0800 (PST)
Message-ID: <80ab0a99-5da2-4274-8350-03ec2d79919d_at_x22g2000yqx.googlegroups.com>
On Feb 15, 8:07 pm, Tegiri Nenashi <tegirinena..._at_gmail.com> wrote:
>
> The more I study relational model, the less I appreciate the concept
> of type (domain). This is consistent with dbms vendors failed to
> deliver genuine rdbms extensibility via user defined types: when did
> you last time program a new type? It looks like the only important
> operation on any domain is equality, and the other ones are just
> predicates in disguise.
It seems to me operators only apply to types of entities in a defined algebraic structure like a field (I hope that's right, I'm no mathematician). Still, they're absolutely necessary for those cases - how else could we do things like number arithmetic, string slicing, point translation, shape scaling and rotation, line intersection, color mixing, matrix multiplication, polynomial addition, regexp concatenation, and so on in a database? Granted, we can't do most of those things now because of lack of vendor domain support, but I'm not ready to give up on types yet.
I agree with your point about predicates, though. Most entities require no operators except equality (and perhaps constructors). I just wish those teaching programming and databases knew this. The database design module I completed last year was pure ER diagrams, everything-is-an-attribute-of-an-object and not a single mention of predicates. So too the OO design patterns module, and the OOAD modules the year before. Received on Tue Feb 16 2010 - 10:47:42 CET