Re: On formal HAS-A definition
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 08 May 2010 23:00:14 -0300
Message-ID: <4be61731$0$12462$9a566e8b_at_news.aliant.net>
>
> A vehicle that never has had nor can have tires is not a car. If the car is
> on blocks, then even though its tires have been removed, they're still the
> car's tires. A car that is still on the assembly line also has tires--even
> if they haven't yet been ordered. If someone were to ask, "Where are that
> car's tires?" It would be really strange to hear an answer like "there
> aren't any." Instead, one might say, "they've been put on another car," or
> "they're on order," or "they've been stolen."
>
> An amputee's limb is still his limb even though it has been removed, but
> even so, having four limbs isn't essential to being a human, whereas having
> tires is essential to being a car.
Date: Sat, 08 May 2010 23:00:14 -0300
Message-ID: <4be61731$0$12462$9a566e8b_at_news.aliant.net>
Mr. Scott wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:4be5b09f$0$26945$9a566e8b_at_news.aliant.net...
>
>>Mr. Scott wrote: >> >> >>>"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message >>>news:4be59bfa$0$12451$9a566e8b_at_news.aliant.net... >>> >>> >>>>Mr. Scott wrote: >>>> >>>> >>>> >>>>>"Mr. Scott" <do_not_reply_at_noone.com> wrote in message >>>>>news:Atqdnbh1eNZ_YX7WnZ2dnUVZ_g-dnZ2d_at_giganews.com... >>>>> >>>>> >>>>> >>>>>>"Tegiri Nenashi" <tegirinenashi_at_gmail.com> wrote in message >>>>>>news:0b0623a8-7a8c-476b-8de2-78c31a36ab17_at_f17g2000pra.googlegroups.com... >>>>>> >>>>>> >>>>>> >>>>>>>Again, I didn't research literature, but here is my shot: the HAS-A is >>>>>>>an inclusion dependency. Example: >>>>>>> >>>>>>>Dept = [DeptNo DeptName] >>>>>>> 10 Accounting >>>>>>> 20 Research >>>>>>>; >>>>>>> >>>>>>>Emp = [DeptNo EmpName] >>>>>>> 10 King >>>>>>> 10 Smith >>>>>>>; >>>>>>> >>>>>>>Formally: >>>>>>> >>>>>>>Emp v (Dept ^ []) < Dept v (Emp ^ []). >>>>>>> >>>>>>>I suppose HAS-A shares many unconvenient properties with set >>>>>>>membership, for example, it is not transitive. Consider >>>>>>> >>>>>>>Accounts = [EmpName Institution] >>>>>>> Smith BoFA >>>>>>> Smith WellsFargo >>>>>>>; >>>>>>> >>>>>>>the it is not the case that "Dept HAS-A Accounts". Again, the naming >>>>>>>problem raises its ugly head: why would the first attributes be called >>>>>>>"EmpName" rather than "PersonName"? >>>>>>> >>>>>>>More important: is this correct formalization? Specifically, shouldn't >>>>>>>functional dependency >>>>>>> >>>>>>>Dept # DeptNo < Dept # DeptName >>>>>>> >>>>>>>be a part of HAS-A constraint definition? >>>>>> >>>>>>I don't think nontrivial functional dependencies have any bearing on >>>>>>whether or not there is a 'has-a' relationship; instead, it is the >>>>>>juxtaposition of attributes in a relation scheme under the convention >>>>>>that it is not just components that are significant but also tuples. >>>>>>If there is a mapping from tuples into the domain of discourse, then it >>>>>>follows that the components of a tuple map to parts of the whole that >>>>>>the tuple maps to. >>>>> >>>>>One could argue that a trivial functional dependency from the superkey >>>>>that consists of the entire heading of a relation to any proper subset >>>>>of the heading specifies a 'has-a' relationship. >>>>> >>>>>I should also point out that because 'has-a' relationships are in >>>>>essence part-whole relationships, that they are transitive. For >>>>>example, cars have tires; tires have rims; therefore, cars have rims. >>>> >>>>Except that not all cars have tires--some are on blocks. We could just as >>>>legitimately say that all tires have cars. >>> >>>Without tires, there is no car, but it is not necessary for a car's tires >>>to be physically attached for them to be part of the car. >> >>That's absurd. A car without tires remains a car just as an amputee >>remains a human being.
>
> A vehicle that never has had nor can have tires is not a car. If the car is
> on blocks, then even though its tires have been removed, they're still the
> car's tires. A car that is still on the assembly line also has tires--even
> if they haven't yet been ordered. If someone were to ask, "Where are that
> car's tires?" It would be really strange to hear an answer like "there
> aren't any." Instead, one might say, "they've been put on another car," or
> "they're on order," or "they've been stolen."
>
> An amputee's limb is still his limb even though it has been removed, but
> even so, having four limbs isn't essential to being a human, whereas having
> tires is essential to being a car.
You are a complete fucking idiot. Received on Sun May 09 2010 - 04:00:14 CEST