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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: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Mon, 04 Jul 2005 20:13:10 GMT
Message-ID: <qLgye.137278$Nn7.7012386@phobos.telenet-ops.be>


Jon Heggland wrote:
> In article <NBAxe.135734$rx6.7273595_at_phobos.telenet-ops.be>,
> jan.hidders_at_REMOVETHIS.pandora.be says...
>

>>>>Not really, I'm restricting it slightly. I'm using the one that says 
>>>>that a value is something that (1) has one or more representations, 
>>>>i.e., can be encoded in memory and (2) is identified by that encoding in 
>>>>the sense that some equivalence relation over all possible 
>>>>representations is defined and each value corresponds to an equivalence 
>>>>class defined by it.
>>>
>>>This sounds just like D&D's definition in TTM. But a lexical object is 
>>>not a value, it is the representation of a value? What then is a lexical 
>>>object *type*?
>>
>>A set of values.

>
> Let me try to sum up.
>
> A value has one or more representations.

Yes, but note that that was true in *my* definition of value. In ORM terminology the notions of value and representation are usually considered synonymous.

> A lexical object is a representation, not a value.

Again, under my definition of value. In ORM's vocabulary this would not be true.

> A lexical object type is a set of values.

Yep, although it would probably have been less confusing if I would have said it was a set of representations. My apologies for that.

Received on Mon Jul 04 2005 - 15:13:10 CDT

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