Re: Love or hate, or? domains with cardinality two

On 2015-11-17 22:56:59 +0000, Erwin said:

> Op dinsdag 17 november 2015 21:36:54 UTC+1 schreef Nicola:

>> On 2015-11-17 19:45:57 +0000, Erwin said:
>> 
>>> Op maandag 16 november 2015 22:09:14 UTC+1 schreef Nicola:
>>>> ...
>>>>> ???
>>>>> 
>>>>> 
>>>>> 
>>>>> (DEPARTMENT NOTMATCHING EMPLOYEE) SUBSET-OF FI
>>>>> 
>>>>> plus a key declaration {dept} on the view EMPLOYEE WHERE mgr
>>>> 
>>>> Somehow I expected that :) What is FI?
>>>> 
>>>> Nicola
>>> 
>>> What I actually should have replied :
>>> 
>>> Well to me it's clearly not "not straightforward" and if you expected
>>> it, why claim it is [not straightforward] ?
>> 
>> If I interpret correctly your constraints, you've got them wrong, because
>> they allow a department without a manager.
>> 
>> Nicola

Point taken.

This highlights the importance of the succintness of the language, not only the expressiveness. Constraints expressed algebraically are in many cases more succint
than their counterpart in first-order logic (think of division).

SQL is nowhere near that, and when I think of something not being straightforward,
my opinion is biased by the thought that it needs to be eventually implemented in
SQL. That said, my argument is still valid: using a different schema design would allow
you to simplify the above constraint even further, so it is correct that the above
is not the *most* straightforward constraint ;)

Nicola

• news://freenews.netfront.net/ - complaints: news_at_netfront.net ---