Re: Indexes and Logical design
Date: Sat, 10 Sep 2005 20:36:05 GMT
"VC" <boston103_at_hotmail.com> wrote in message
> "David Cressey" <david.cressey_at_earthlink.net> wrote in message
> >If we're going to take away the pointers they love
> > to play with, we'd better throw them a bone. Indexes fill that bill.
> I do not understand the above. Are you talking about some psycological
> problems that can be settled if the hypothetical, non-database,
> would know tha some table has indexes ?
> You are right of course that constraints are part of the logical model.
> However, the unique index is not. Such index is just an implementation
> vehicle for a unique constraint. Besides, in Oracle (with which you are
> apparently familiar) , a unique constraint can be enforced via a
> index. This piece of trivia should make it clear that an index, either
> unique or non-unique, is just a trick to improve performance. One can
> easily imagine a unique constraint enforcement without any index
> although such enforcement would be impractical.
> > Fourth, the DEC Rdb/VMS command "show table" shows the indexes as
> > of
> > its display.
> Surely, you realize that it's just an impementation pecularity, a
> convenient tool for the DBA.
Life is full of "implementation peculiarities". So far you've dismissed
Oracle, Rdb, and Data Architect
peculiarities as unimportant. What's left?
> Well, as a database designer, you convert your conceptual simplification
> of the 'real world' into a logical model and then you think how to
> this model using various tools at your disposal (indexes being one of
> them). Such impementation would be your physical model.
Nope. There is more than one logical model that corresponds to the same conceptual model. You make choices based on the probable consequences downstream, after implementation. Some of this is hunch work, and not strictly mechanical.