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Re: Example of expression bias?

From: J M Davitt <jdavitt_at_aeneas.net>
Date: Wed, 21 Jun 2006 01:35:50 GMT
Message-ID: <Wn1mg.76983$YI5.4098@tornado.ohiordc.rr.com>


paul c wrote:
> Tony D wrote:
>

>> ...
>>
>>> A data type in RM = (a domain1 to draw values from) + (restrictions
>>> implemented on domain1 --> domain constraint) + (operators that can be
>>> defined using that data type)
>>> ...
>>
>> This may be one definition of a data type (not quite one I'd accept, as
>> we've thrashed over elsewhere), but there is nothing particular to RM
>> about this.
>> ...

>
> "domain constraint" seems an uncommon term to me because we usually talk
> of constraints on relations. but I often puzzle over constraints,
> thinking that they could be as fundamental as any other notion, e.g.,
> once one arrives at a similar conception of relations to Codd's, one
> could view everything that one does with them as either adding or
> subtracting constraints.

CJD calls them type constraints; they define the set of values that constitute the type. Types are named, so the sets are named.

The only thing I'd argue about in Cimode's definition is that operators are part of the data type. In fact, D+D make the point that the declaration of operators is orthogonal to the declaration of types -- given that the types are extant before the operators.

>
> p
Received on Tue Jun 20 2006 - 20:35:50 CDT

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