Re: Objects and Relations

On Feb 19, 10:42 pm, "JOG" <j..._at_cs.nott.ac.uk> wrote:
> On 19 Feb, 01:01, "David BL" <davi..._at_iinet.net.au> wrote:
>
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> > On Feb 18, 12:36 am, "JOG" <j..._at_cs.nott.ac.uk> wrote:
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> > > 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.
>
> > Are you making a real attempt to understand me? That's a trivial
> > strawman. It clearly wasn't a definition.
>
> Apologies if you thought it was tangential, but I feel your definition
> of an entity (or lack thereof) indicates the concepts lack of utility /
> as a whole/. This is an underlying problem I have with the whole
> 'entity' line of thought, and not just in the conversation with
> yourself.
>
> However if you are saying an entity isn't a type, well that goes
> against the premise of Entity/Relationship modelling, which itself has
> such a big role in the current data management field. Again why are
> you using different definitions?

I cannot say for sure but I don't believe your definition of entity follows the convention. The following is quoted from Wikipedia

    http://en.wikipedia.org/wiki/Entity-Relationship_Model

    "Entity-relationship diagrams don't show single     entities or single instances of relations. Rather,     they show entity sets and relationship sets     (displayed as rectangles and diamonds respectively).     Example: a particular song is an entity. The     collection of all songs in a database is an entity     set."

> 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.

> 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.

> 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. Received on Tue Feb 20 2007 - 02:22:29 CET