Re: Pizza Example

Cutting slack is a two way street. You could cut other people some slack, and recognize that anyone who expresses a relational model in the form of SQL CREATE commands is probably going to include some features of the physical data model as well as features of the logical model.

Choosing an upper limit of 30 was not inherent in the logical data model.

It might have been (assumption) inherent in the domain definition of the data requirements. A limit on the number of characters IS, after all, a domain constraint. If its conceptual it is discovered, not designed, and is in the conceptual data model as well as the logical data model.

Or it might have been invented at the time the logical model was converted to a physical model, for reasons like storage capacity or throughput (again, an assumption).

Also, what's the big deal? If thirty turns out to be too low, then just ALTER the column to make it forty. A good RDBMS will do that for you, and pad the existing data with blanks. Of course that could wreak havoc with data independence, when users of the data try to stuff a 40 character data value into a 30 character working storage variable. But you can't have everything, can you? Received on Mon Apr 05 2004 - 19:50:52 CEST