Re: On Formal IS-A definition
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Mon, 03 May 2010 19:42:54 -0300
Message-ID: <4bdf5177$0$12440$9a566e8b_at_news.aliant.net>
>
> I didn't comment on those points.
>
>
>
> That's what I wrote, didn't I? It's strange. It's very unusual.
> It doesn't fit in with ER modelling, for instance.
>
>
>
> Thus far I can agree with you: naming isn't really part of
> the modelling mathematically, and using strange names doesn't
> make a model any more correct or incorrect in mathematical terms.
>
> But this isn't my main argument against your interpretation
> of IS-A. THe main argument is the following.
>
>
>
> I was trying to sidestep the issue of attribute (re)naming here,
> because it is beside the main point of the example, which is that
> according to your definition, the same relation (Herbivores)
> has two different IS-A relations, one with Animals and
> one with Vegetables. I know multiple inheritance in
> programming languages tends to be used in just this kind
> of way (with "mixin classes" for instance) but I think with
> such a notion the name "IS-A" is just wrong. It's fine to have
> your proposed notion but give it a different name: call it a role
> or something. A Herbivore just isn't a Vegetable.
>
> I know this is again an argument about naming, but this time
> it's about the name "is a" itself.
Date: Mon, 03 May 2010 19:42:54 -0300
Message-ID: <4bdf5177$0$12440$9a566e8b_at_news.aliant.net>
Reinier Post wrote:
> Tegiri Nenashi wrote:
>
>>On Apr 29, 2:31 pm, r..._at_raampje.lan (Reinier Post) wrote: >> >>>Tegiri Nenashi wrote: >>> >>>[...] >>> >>> >>>>Animals = [Name] >>>> bear >>>> sheep >>>> wolf >>>>; >>> >>>>Carnivores2 = [Name Prey] >>>> bear deer >>>> wolf sheep >>>> wolf deer >>>>; >>> >>>>I suggest that we still have "Carnivores2" IS-A "Animals". Do you >>>>agree? >>> >>>No. I've never seen this. The naming of Carnivores2 >>>is strange: it should name what each tuple stands for, >>>but a carnivore isn't always represented by a single tuple. >> >>Just to remove any confusion about Carnivores2 name origin: >>1. It is plural because of convention to name relations as sets of >>things >>2. The number two is version number designed to distinguish this >>relation from Carnivores1
>
> I didn't comment on those points.
>
>
>>Perhaps you are not comfortable with the idea than more than one tuple >>of Carnivores2 might represent each "entity"?
>
> That's what I wrote, didn't I? It's strange. It's very unusual.
> It doesn't fit in with ER modelling, for instance.
>
>
>>At this moment I can't >>suggest a convincing argument other than vague intuition that database >>theory should deviate from explicit mentioning tuples (and attributes, >>for that matter, either). All information should be presented in terms >>of constraints, expressed in relational algebra terms.
>
> Thus far I can agree with you: naming isn't really part of
> the modelling mathematically, and using strange names doesn't
> make a model any more correct or incorrect in mathematical terms.
>
> But this isn't my main argument against your interpretation
> of IS-A. THe main argument is the following.
>
>
>>>Suppose we have >>> >>> Herbivores = [Name Foodtype] >>> deer grass >>> rabbit grass >>> rabbit carrots >>> >>>and >>> >>> Vegetables = [Foodtype] >>> grass >>> carrots >>> >>>Would you say that Herbivores IS-A Animals? >>>What about Herbivores IS-A Foodtype? If not, why not? >> >>Wouldn't >> >>Vegetables = [Name] >> grass >> carrots >> >>be a more appropriate choice? Then, we can combine Animals and >>Vegetables into LivingThings. Attribute naming seems to be a tricky >>subject in Relational Model...
>
> I was trying to sidestep the issue of attribute (re)naming here,
> because it is beside the main point of the example, which is that
> according to your definition, the same relation (Herbivores)
> has two different IS-A relations, one with Animals and
> one with Vegetables. I know multiple inheritance in
> programming languages tends to be used in just this kind
> of way (with "mixin classes" for instance) but I think with
> such a notion the name "IS-A" is just wrong. It's fine to have
> your proposed notion but give it a different name: call it a role
> or something. A Herbivore just isn't a Vegetable.
>
> I know this is again an argument about naming, but this time
> it's about the name "is a" itself.
I thought Clinton settled this whole issue already. Cigar anyone? Received on Tue May 04 2010 - 00:42:54 CEST