Re: Another view on analysis and ER

From: JOG <>
Date: Fri, 14 Dec 2007 04:00:39 -0800 (PST)
Message-ID: <>

On Dec 13, 12:26 am, Jan Hidders <> wrote:
> On 11 dec, 12:37, JOG <> wrote:
> > On Dec 10, 6:33 pm, Jan Hidders <> wrote:
> > > On 9 dec, 22:10, JOG <> wrote:
> > > > On Dec 9, 5:20 pm, Jan Hidders <> wrote:
> > > > > On 9 dec, 04:04, JOG <> wrote:
> > > > > > Now in ontology, it is generally accepted that an
> > > > > > object, or entity, is nothing more than a compressence of a collection
> > > > > > of properties - i.e. (attribute, value) pairs.
> > > > > [....]
> > > > > I'm also not comfortable with the usage of "is" here. I'd agree that
> > > > > this is how entities can be described, but saying that they "are"
> > > > > these descriptions seems wrong to me.
> > > > Why are you uncomfortable with that. An entity is nothing more and
> > > > nothing less than the 'compressence' of its _full_ set of all its
> > > > attributes.
> > > > > After all, different descriptions may describe the same entity.
> > > > Well, I haven't talked about describing entities, rather we're
> > > > defining them. This is an entity as our model sees it, not how it is
> > > > seen in the real world (obviously there are concessions, given the set
> > > > of possible attributes is probably infinite).
> > > But that is what I'm saying, isn't it? These sets of properties are
> > > part of your model of a piece of reality and as such *represent*
> > > entities that are part of that reality, Saying that they *are* these
> > > entities is sloppy use of language and confuses the map with the
> > > territory. If I didn't know any better I'd almost think you could be
> > > accused of muddled thinking. :-)
> > Ha, I'll have you know that it would only be a case of muddled writing
> > not muddled thinking sir! In my defence I'd refer you back to some
> > posts I made a while back in another thread where I was promoting a
> > distinction between a "construct" and an "entity" to try and avoid the
> > very ambiguity that you are talking about. I hold little hope of
> > changing anyones terminology though, however worthwhile I think that
> > would be ;)
> Just our own terminology for the duration of this discussion seems
> ambitious enough. :-) At least it seems we're on the same page here,
> so that's nice. Btw. what is the difference between your internal
> entity / construct and a tuple with named fields?

The construct/entity might well be encoded as a tuple, but there may be a host of other valid encodings. I would not want the concept be seen as tied to an RM encoding, nor constrain it to being viewed as a finite partial function. I would rather see it in a more general fashion as a mathematical relation between attributes (a name and a domain) and values (objects/entities/whatever), over which one might apply all the facilities that set theory can accord.

> > I would say though that the internal entity (henceforth referred to as
> > a construct by myself) and the external entity, /must/ share the same
> > identifiers for them to be consistent with each other. Its a simple
> > rule, but without it one ends up in a artificial quagmire of hidden
> > surrogates or OID's (which have no correspondence whatsoever with data
> > as observed out in the wild), or worse still, broken databases.
> That is something that you still have to show. To me it is very clear
> what OIDs correspond to: they correspond the entities we want to
> represent.

Well, I have never suggested that anyone doesn't understand what an OID corresponds to. The concern is the fact they are superfluous and facilitate results which have no correspondence to the real world with which we are modelling - they add nothing that cannot be achieved with content-based addressing. But then this is all well documented by date, pascal, darwen, etc.

Ought I infer that you don't agree with their perspective? That somehow all of an entity's properties can change and yet, because it has an OID, it is magically the same thing? No theory of identity that I have ever read would accede to such a view (even substance theorists), and yet it perpetuates in computer science due to the familiarity we all have with memory allocation. And let me preempt the argument for OID's and hidden surrogates that follows that suggestion that are necessary due to the distinction between modelled entities and their external counterparts - it does not stand due to the requirement of /identifiable/ correspondence between the two.

> These, by definition, can be observed in the wild, at least
> in the sense that is relevant here.

Entities or OID's can be observed in the wild? OID's I disagree 100%. And in the sense that the world around us has no innate partitioning, entities are constructed rather than observed. And then to subsequently recognize them again we observe identifying properties.

> So as far as I am concerned you
> are just introducing an ad hoc rule for no other reason than that it
> seems to lead to the conclusion you were trying to prove, namely that
> your construct is the best way of representing entities in a database.

Well, I certainly hope not. I have started from base principles of how we identify items, looked to a valid representation in set theory, and continued from there. I see no ad-hoccity, but if you do, then great, lets stamp on it ;)

> -- Jan Hidders

All best, J. Received on Fri Dec 14 2007 - 13:00:39 CET

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