Re: Relation Definition

Dawn M. Wolthuis wrote:
>
> Is this one from Date the best in the industry?

No. Of all the formal definitions of the relational model I have seen his is probably the clumsiest. For the authorative ones that real database theorists use see the definitions in the Alice book:

  http://portal.acm.org/citation.cfm?id=551350

To summarize, when it is sufficient the "subset of cartesian product" definition is used, and when the names of the columns are relevant for the discussion at hand the definition goes roughly something like the following:

Def. [Tuple] A *tuple* is a partial function that maps column names to domain values and is defined for a finite set of column names which is called its *header*.

Def. [Relation] A *relation* is a set of tuples that all have the same header.

There, that wasn't so hard now, was it? :-)

• Jan Hidders