Re: Concurrency in an RDB - another question about recursive definitions
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 21 Jan 2007 17:51:52 GMT
Message-ID: <YKNsh.3606$1x.61956_at_ursa-nb00s0.nbnet.nb.ca>
>
>
> Let's just say confusing a relation with a domain is a blunder. Using
> the same name to refer to a relation and a domain is not necessarily a
> blunder provided everyone agrees that relations and domains with the
> same name are not the same thing.
>
> Consider a system with Person, Name, Date and Integer domains. Might the
> following compile?
>
> CREATE RELATION Person (
> Person Person
> , Name Name
> , DOB Date
> , #Dependents Integer
> )
>
> It might compile provided the language can always contextually
> distinguish between relation names, attribute names and domain names.
> Would it be a good idea to create such a relation? That's a matter of
> opinion.
Date: Sun, 21 Jan 2007 17:51:52 GMT
Message-ID: <YKNsh.3606$1x.61956_at_ursa-nb00s0.nbnet.nb.ca>
Bob Badour wrote:
> paul c wrote:
>
>> Bob Badour wrote:
>>
>>> paul c wrote:
>>> ...
>>>
>>>> Given relation : B = { {a,b} | a in A and b in B } /* Using C-style
>>> ^
>>> |
>>> Relations are not domains ----------------------/
>>
>> Thanks and okay, to put it bluntly, I take it that using B to stand
>> for a relation in this way is nonsense.
>
>
> Let's just say confusing a relation with a domain is a blunder. Using
> the same name to refer to a relation and a domain is not necessarily a
> blunder provided everyone agrees that relations and domains with the
> same name are not the same thing.
>
> Consider a system with Person, Name, Date and Integer domains. Might the
> following compile?
>
> CREATE RELATION Person (
> Person Person
> , Name Name
> , DOB Date
> , #Dependents Integer
> )
>
> It might compile provided the language can always contextually
> distinguish between relation names, attribute names and domain names.
> Would it be a good idea to create such a relation? That's a matter of
> opinion.
And of course, one could argue I made a blunder above by possibly confusing a value with a variable. Values, variables and domains/types all being very distinct.
[snip] Received on Sun Jan 21 2007 - 18:51:52 CET