Re: Objects and Relations

On Feb 17, 3:05 pm, "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.

Your definition is meaningless as has been pointed out by several people. entity = particular thing, just begs the question of what a 'thing' is. You seem to have a circular definition that a thing = a particular entity.

> Why are you doing that?

I am trying to help you to a better definition, from which the limits of thinking in terms of 'entities' becomes clearer.

If it helps given the E/R-style 'entity' terminology you are holding onto, you might consider that I view /everything/ as an "associative entity". But of course I would not call it 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).

It is good we are agreed of the benefit there, and an important point not to forget in all of this.

>
> What is more fundamental - facts about a particular entity, or the
> entity itself? Surely the facts are secondary - at least for physical
> entities.

Well of course I don't accept there is anything but facts and values, so your question is nonsensical to me.

Remember that there are practical evidence of this standpoint having merit. For instance Symbolic AI died in the 1970's - a very real, practical example of how tyring to manipulate these elusive 'entities' results in failure. Situated and Nouvelle AI was born from this and I'd encourage you to check this area out - "Elephants don't play chess" by Brooks, is a good starting point.

>
> 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.
Received on Sat Feb 17 2007 - 16:36:31 CET