Ben Sizer wrote:
> It's not a crackpot theory. It's a completely reasonable theory. SQL is
> based on relational algebra, which provides a mathematical set of
> operators for grouping data that is stored in separate sets. That data
> is selected and projected according to its value, and nothing else. The
> concept of it having a 'type' has been overlaid on top of this,
> presumably to facilitate efficient implementation, which tends to
> require fixed-width rows (and hence columns). It's not necessary in any
> sense, and it's reasonable to argue that if it was trivial to implement
> variable width columns as efficiently as fixed width columns, that
> explicit data types might never have needed to exist.
The mathematical definition of the relational model includes
that data values are drawn from specific sets. Implementing
variable width columns has nothing to do with it. Here's the
reference:
1.3. A Relational View of Data
The term relation is used here in its accepted mathematical
sense. Given sets S1, S2, ยทยทยท, Sn, (not necessarily
distinct), R is a relation on these n sets if it is a set
of n-tuples each of which has its first element from S1,
its second element from S2, and so on [1]. We shall refer to
Sj as the jth domain of R.
[Footnote 1:] More concisely, R is a subset of the Cartesian
product S1* S2 * ... * Sn.
-- E. F. Codd. "A Relational Model of Data for Large Shared
Data Banks." /Communications of the ACM/, Vol. 13, No. 6,
June 1970, pp. 377-387.
--
--Bryan
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