Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]
Date: Mon, 11 Jul 2005 12:19:31 +0200
In article <1120833398.573397.92590_at_o13g2000cwo.googlegroups.com>,
> > Your zipcode is either a string or a number. A value with (say) two
> > possreps has two representation, not just the one xor the other.
> My zipcode is either a tagged string or a tagged number. If a value
> with two possreps is thought of as having two "representations" at the
> same time than it's a record/structure (see above). Btw, does the
> T.D. say the definition implies that two possreps *exist* at the same
> time or it's your own interpretation ?
From RM prescription 4: Actual vs. possible representations (page 110, TTM 1st ed.):
For each declared possible representation PR for [the scalar type] T, a selector operator S shall automatically be defined with the following properties: [...] b. Every value of T shall be produced by some invocation of S.
Will that do?
-- JonReceived on Mon Jul 11 2005 - 12:19:31 CEST