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Home -> Community -> Usenet -> comp.databases.theory -> Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Mon, 11 Jul 2005 12:19:31 +0200
Message-ID: <MPG.1d3c661fe1a32dfc9896f6@news.ntnu.no>


In article <1120833398.573397.92590_at_o13g2000cwo.googlegroups.com>, boston103_at_hotmail.com says...
> > 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?

-- 
Jon
Received on Mon Jul 11 2005 - 05:19:31 CDT

Original text of this message

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