Re: On formal HAS-A definition
From: Mr. Scott <do_not_reply_at_noone.com>
Date: Sat, 8 May 2010 23:36:40 -0400
Message-ID: <Afydnd_nnuBUsHvWnZ2dnUVZ_v2dnZ2d_at_giganews.com>
> And yet a railcar doesn't have tires and only some subway cars have tires.
> In fact, I believe the first use of car referred to conveyances on iron
> wheels. But put my subjectivity aside, all that matters in db design and
> usage is agreement among a db's users as to what the attributes stand for
> (I believe this is both an advantage as well as a requirement and the
> Information Principle encourages adherence). Some of those users might
> even need to suppress their cultural biases. The subjective and
> doctrinaire stuff doesn't belong here no matter important people such as
> Celko try to make it sound because they have an interest in promoting
> dull, lazy minds in the db population. Same goes for obscure set axioms
> that would appear to prevent users from thinking of sets of people, not
> just animals, unless those approaches can lead to some practical
> advantage. Why theorists would argue about such meanings is beyond me.
Date: Sat, 8 May 2010 23:36:40 -0400
Message-ID: <Afydnd_nnuBUsHvWnZ2dnUVZ_v2dnZ2d_at_giganews.com>
"paul c" <toledobythesea_at_oohay.ac> wrote in message
news:hpnFn.3687$z%6.2949_at_edtnps83...
> 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. >
> And yet a railcar doesn't have tires and only some subway cars have tires.
> In fact, I believe the first use of car referred to conveyances on iron
> wheels. But put my subjectivity aside, all that matters in db design and
> usage is agreement among a db's users as to what the attributes stand for
> (I believe this is both an advantage as well as a requirement and the
> Information Principle encourages adherence). Some of those users might
> even need to suppress their cultural biases. The subjective and
> doctrinaire stuff doesn't belong here no matter important people such as
> Celko try to make it sound because they have an interest in promoting
> dull, lazy minds in the db population. Same goes for obscure set axioms
> that would appear to prevent users from thinking of sets of people, not
> just animals, unless those approaches can lead to some practical
> advantage. Why theorists would argue about such meanings is beyond me.
I think you're oversimplifying. It is necessary for there to be agreement not only on what attributes stand for, but also on what components and sets of components stand for. The propositions represented by tuples in the database are not logical truths but rather analytic truths, which involve valuation and assignment under a particular interpretation.
I must admit that I should have just ignored Bob's stupid remark concerning tires having cars, but I decided to give him the benefit of the doubt. Unfortunately, he is very good at baiting people, and this time I fell into his trap. Never again, though. I perceive no great loss in putting him in the killfile. I can't remember the last time that he contributed anything novel or worthwhile or even constructive--at least nothing that can't be found in my copy of TTM. Received on Sun May 09 2010 - 05:36:40 CEST