Re: Love or hate, or? domains with cardinality two
From: Nicola <nvitacolonna_at_gmail.com>
Date: Mon, 16 Nov 2015 22:09:11 +0100
Message-ID: <n2dglm$hft$1_at_adenine.netfront.net>
>> On 2015-11-10 18:21:54 +0000, Gene Wirchenko said:
>>
>> On the Employee(id, dept, mgr : boolean) schema, the constraint by which
>> at any time each department has one and only one manager may be formalized
>> as follows:
>>
>> forall x (Department(x) -> (exists y (Employee(x, y, true)
>> and
>> forall w,z (Employee(x, w, z) and w <> y -> z = false))))
>>
>> This is not the most straightforward constraint
Date: Mon, 16 Nov 2015 22:09:11 +0100
Message-ID: <n2dglm$hft$1_at_adenine.netfront.net>
On 2015-11-16 20:34:27 +0000, Erwin said:
> Op woensdag 11 november 2015 19:36:37 UTC+1 schreef Nicola:
>> On 2015-11-10 18:21:54 +0000, Gene Wirchenko said:
>>> >>>>> And what obvious difficulties? >>>> >>>> If you think there aren't any, show me a straightforward solution (of >>>> course, what is difficult and what is not is largely subjective!). >>> >>> I have not claimed that there were none. >>> >>> You are the one who made the claim that they were obvious. Prove >>> your claim.
>>
>> On the Employee(id, dept, mgr : boolean) schema, the constraint by which
>> at any time each department has one and only one manager may be formalized
>> as follows:
>>
>> forall x (Department(x) -> (exists y (Employee(x, y, true)
>> and
>> forall w,z (Employee(x, w, z) and w <> y -> z = false))))
>>
>> This is not the most straightforward constraint
> > ??? > > > > (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
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