Re: Units of Measurement in the Database Model
Date: Wed, 01 May 2002 11:38:59 GMT
Daniel Dudley wrote:
> "David J. Aronson" wrote in message news:3CBCBCE2.CD7B395C_at_att.net...
> > Daniel Dudley wrote:
> > > "David J. Aronson" wrote
> > ...
> > > > If, as I thought, you were thinking of the "foreign key into
> > > > UoM registry" case, then I agree with all that you said.
> > ...
> > > Right on, although I do dislike the use of the term
> > > "foreign key" when discussing lookup tables.
> > Why? What is your preferred term for such a case?
> How about "lookup value"? ;-)
> A lookup table need not have indexes; indeed, they often
> don't (for reasons given in my previous messages). In
> short, the cost of maintaining an index on a lookup table
> is usually too high to justify its use.
> > When do you prefer to use the term "foreign key"?
> A key (foreign or otherwise) is synonymous with the use of
> an index.
Ah, okay, this explains the difference in our terminologies. Not being a database specialist, I tend to toss terms like "foreign key" around a bit more loosely than you might. In my usual usage, it just means that the values in this column are used as an ID column in another table, whether the lookup in that table uses an index or not. I'll try to be more precise. B-)
(Sorry for the long delay getting back to you; I've been out of town since the day after you wrote the above, without Usenet access. Wife and self are now fully moved from VA to PA....)
-- David J. Aronson, Software Engineer FOR HIRE IN PHILADELPHIA AREA Resume, and other details, online at: http://dja2001.home.att.netReceived on Wed May 01 2002 - 13:38:59 CEST