Re: temporary databases

Mikito,

Queries are only one function of a DBMS.

For all practical purposes, all intervals within a DBMS represent a set of discrete points. As a result, a tuple that has an interval attribute represents a set of discrete propositions. In the absence of any interval attributes, a tuple represents a single proposition.

This affects the integrity function, the manipulation function etc.

Consider an HOURS relation with a single interval column representing the hours of operation and an APPT relation with an interval column representing the time and duration of appointments plus other columns identifying the customer and reason etc.

One would like to declare an integrity constraint that the discrete points represented by any APPT interval are a subset of the points represented by the HOURS relation. Likewise, one would like to declare an integrity constraint that the discrete points represented by all APPT intervals are unique within APPT. One would like uniqueness within the discrete points of time represented by the HOURS relation too.

These constraints are very similar to a foreign key constraint and a candidate key constraint, but they are subtly different due to the intervals. For instance, a traditional foreign key constraint would require that the HOURS relation have the exact intervals in the APPT relation. A traditional candidate key constraint would not prevent overlapping intervals and would thus not enfore uniqueness among the discrete points represented by the intervals.

I recently attended a fascinating seminar by Chris Date on the subject. He is holding the same seminar the week of June 10th in Rome if you are in Europe and can afford to go. (http://www.technologytransfer.it/en/seminars/)

He mentioned that he is writing a book on the subject that should hit store shelves Q4.

Cheers,
Bob Received on Fri Jun 07 2002 - 07:06:56 CEST