Re: Objects and Relations
Date: 19 Feb 2007 18:36:48 -0800
Message-ID: <1171939008.171572.262650_at_s48g2000cws.googlegroups.com>
On Feb 20, 1:22 am, "David BL" <davi..._at_iinet.net.au> wrote:
> On Feb 19, 10:42 pm, "JOG" <j..._at_cs.nott.ac.uk> wrote:
> [snip for length]
> > It seems a lot of the communication
> > problems here are because of you using different terminology to that
> > which is accepted in the field.
>
> I don't know what terminology is used in the field because I'm a
> systems programmer. However I would say that thinking entity means a
> type of thing is quite strange.
I rarely hear the term entity set. I hear people talk of entity types, but more often than not this seems to be shortened to just 'entity' (as opposed to an instance). But who cares. At least I see where the miscommunication stems from.
>
> > Either way, it is better to recognize
> > this gap and bridge it, agreed?
>
> Agreed.
>
>
>
> > > It was in reference to
> > > your book example. For the purposes of stating facts about books, an
> > > entity would be a particular book, not some type "book".
> > > Classification is not necessary. It is irrelevant to the discussion.
>
> > > > > 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.
>
> > > I can't understand your point. From my perspective you appear to make
> > > the simple mistake of thinking that because it's difficult to classify
> > > things, things don't exist!
>
> > Well I can only quote you "Are you making a real attempt to understand
> > me?". I mean you keep quoting "entities are illusionary" , even though
> > we have clarified pages ago the intention of this statement. I think
> > it adequately infers the mistake people often made in assuming that
> > entities are anything but arbitrary concoctions.
> > But furthermore I have already offered that your confusion with the
> > statement is just semantics, and you have ignored this. To clarify one
> > more time, consider an analogy.
>
> > I am saying: "Unicorns don't exist."
> > You are saying "Unicorns do exist, look, I just imagined one"
> > To which I reply "ok unicorns do exist, but they are something just
> > made up in your mind".
>
> I not sure what's point you're making. If you're going to create a
> fiction then you're going to store fiction (in the DB) no matter how
> you think about.
Well the idea is to highlight that your complaint of "entities being real as opposed to illusionary" is all just semantics, and it just depends what "real" means. You keep bringing this up, so it was worth addressing. Hopefully that can be hit on the head now.
I'd say a more important point is that because they are all just made up, we can't ever measure where an entity starts and finishes, where it ovelaps with other entities, and so on. There is no correct way of determing what it is composed of, or what it is part of (In a world of entities do written_papers have an authors property, or the other way around?).So why /ever/ try and wrap that fiction up as an entity type then, with remits, boundaries, and qualified attributes then? Just state propositions (always). I see no added value in ever turning any information into an object.
(or to bring it back to the OP, why would a struct ever be preferable
to a relational encoding?)
>
I imagine it probably is.
('Course, don't forget I didn't think your intiial conjecture was
testable, or that its comparison made sense.)
>
> > Does that make more sense as to the semantic difference that you are
> > (perhaps) obsessing over, but now seems to preventing further
> > conversation?
>
> I would suggest we avoid generalised statements and use examples to
> clarify what is meant. I agree that definitions of terms is a likely
> cause of difference of opinion.
> > > I ask again, what's you point about the difficulties of
> > > classification?
>
> > What difficulties?
>
> You pointed out (correctly) that it is difficult to have a type called
> "book" and to know what attributes it should have.
>
> I regard that as a classification problem. It doesn't imply that a
> particular entity is illusionary or subjective.
>
>
>
> > > > 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.
>
> > > I guess your statement that entities are illusionary is nonsensical to
> > > yourself as well then.
>
> > > > 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.
>
> > No comment on this? I've offered to points indicating to how thinking
> > in terms of entities can be unproductive - the lack of success of E/R
> > modelling in replacing RM (which was its original goal), and the
> > collapse of the entity-based manipulation of Classical AI in the 70's.
> > There is insight in both of these.
>
> IMO the insight in the first is the difficulty of an objective
> classification of things.
>
> The second I cannot properly comment on - I'm out of my depth. My
> impression is that AI in general hasn't lived anywhere near to the
> original promises and there are more explanations than you can poke a
> stick at. One explanation I favor is that it is difficult to close
> the association between reasoning and meta-reasoning, leading to the
> so-called ghost in the machine. I find it telling that it's not
> generally possible to apply one's own high level understanding of
> "truth" to the very sentences that are used to reason about those
> truths. As a simple example, 3+4 and 7 are equal and yet not equal.