Re: c.d.theory glossary - NULL
Date: Tue, 27 Apr 2004 12:18:40 -0400
And here's another difference between a logical model and a physical model.
In a logical model,
if you are using relations as your modeling tool, then NULLS should not be allowed. The reason?
NULLS can't exist in a relation.
In the physical model, if you a modeling in terms of tables, rows and columns, there's no real reason to forbid NULLS in every column. Some columns should have NULLS forbidden in order to maintain entity integrity, but optional data is a possibility. Received on Tue Apr 27 2004 - 18:18:40 CEST