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Re: Example of expression bias?

From: paul c <toledobythesea_at_oohay.ac>
Date: Wed, 21 Jun 2006 01:41:07 GMT
Message-ID: <Ts1mg.68637$Mn5.61432@pd7tw3no>


J M Davitt wrote:

> 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.
> ...

what do you say? is there such a thing as relation constraints?

p Received on Tue Jun 20 2006 - 20:41:07 CDT

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