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Re: Objects and Relations

From: Cimode <cimode_at_hotmail.com>
Date: 17 Feb 2007 08:25:08 -0800
Message-ID: <1171729507.948439.110800@a75g2000cwd.googlegroups.com>


On 17 fév, 16:05, "David BL" <davi..._at_iinet.net.au> wrote:
> On Feb 17, 12:18 am, "JOG" <j..._at_cs.nott.ac.uk> wrote:
>
> > On Feb 16, 4:40 am, Joe Thurbon <use..._at_thurbon.com> wrote:
> > > David BL wrote:
> > I am happy to put up with the definition of an entity describing a set
> > of attributes/value pairs. All I object to is the concept that these
> > sets are anything but arbitrary collections.
>
> > To some people a 'book' requires an attribute stating whether it is a
> > hardback or a softback. In other contexts a book might just be
> > composed of its title, its content, etc. (a book published online
> > perhaps). Please don't dwell on this example, it is just off the top
> > of my head to show that 'entities' are artifices and vary incredibly
> > from person to person and context to context. So as far as data
> > management is concerned, keep 'entities' out, and let humans resolve
> > such concepts outside of the logical model.
>
> You seem to be focusing on entity as meaning an abstract type, whereas
> I'm tending to think of an entity as a particular thing. Why are you
> doing that? It is well known that classification of entities is
> adhoc. Fortunately In DB systems we tend to state facts about
> particular things far more often than sets of things.
>
> If I were to place an actual book in front of you, you could think of
> hundreds of objective propositions about it. Actually the number of
> possible propositions you could state about the book would seem almost
> unlimited.
>
> If you were given a different book, again there would be countless
> propositions you could state about it. Now the book may have some
> fundamental differences. Therefore attributes relevant to the first
> book may not make sense for the second book and vice versa. This
> makes classification of books difficult. However we both agree that
> the RM copes well with that because it can represent knowledge about a
> single book across lots of different relations. RM has no need to
> develop a class hierarchy in the manner of OO (or indeed E/R
> diagrams).
>
> What is more fundamental - facts about a particular entity, or the
> entity itself? Surely the facts are secondary - at least for physical
> entities.
>
> Now you might argue that the situation changes as the entities become
> more nebulous. For example a company like Microsoft is not
> particularly well defined. However, to me that just means that some
> facts that one might state about Microsoft will be subjective or
> vague. Does this fuzzyness show that entities or facts are more
> fundamental? I would say neither because both the entity and the
> facts about it are fuzzy.

I hope you realize now that you won't get any education from people here...I suggest you do some reading then make up your mind..;) Received on Sat Feb 17 2007 - 10:25:08 CST

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