Re: Example of expression bias?

From: J M Davitt <>
Date: Wed, 21 Jun 2006 13:03:04 GMT
Message-ID: <csbmg.62591$>

Cimode wrote:

> 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.
>>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.
> No need to argue on that, operators are indeed a part of a data type
> definition.  I would personally define *possible* operators applyable
> at domain level then define attribute *permissible* operators at data
> type level .

Then, would you explain why D+D are wrong? And you should probably elaborate on what the "domain level" and the "data type level" are.

And, while you're at it, explain in which data type definition [sic] an operation like, say, division, defined on integers and returning a rational, belongs?

[snip] Received on Wed Jun 21 2006 - 15:03:04 CEST

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