Re: Another view on analysis and ER

On Dec 9, 1:32 am, Jan Hidders <hidd...@xxxxxxxxx> wrote:
On 8 dec, 21:37, JOG <j...@xxxxxxxxxxxxx> wrote:



My question is when should one choose to represent (in FOL if one so
desires) something as a thing, as in Exists x, or as a predicate, X().
So if I have my previous example "John from London married Jane from
Manchester in a Church", do I have:

1) Married(Husband:John, Wife:Jane, Instituion:Church)
2) EXISTS! x E marriages [ Husband(x, John) ^ Wife(x, Jane) ^
Institution(x, Church) ]

First one is marriage as a predicate, the second one the marriage as a
thing, x. Which to choose, and when.

The most simple one that allows you to model your UoD properly. In the
context of FOL this would usually be 1) except if you also have
predicates in your UoD in which a marriage plays a role as an entity.
In the latter case you should probably use 2) but it could also be
that you have to expand even more and also objectify the relationship
between marriage and husband. Obviously this can repeat itself in
theory an arbitrary number of times, and each time you replace a
relationship with an new entity type and a few new relationships that
represent the roles. In a very real sense you can compare it to
zooming in on a fractal. The design principle can then be formulated
as zooming in as much as is needed to place all the predicates you
have to model, but no more.

Note that in an ER dialect that allows objectification, such as ORM,
zooming in one time can often be dealt with by objectification and
keep the basic structure of the model the same, but the second time it
will change it.

-- Jan Hidders

Ok, thanks for the feedback. I have certainly advanced my
understanding or ERM via these discussions, which I don't often get
the opportunity to do.

But now we're finally on the same page, let me offer my final argument
as to why (at least in data modelling) relationships and entities are
the same things. In my example, where a single proposition could be
written as either,

1) x = Married(Husband:John, Wife:Jane, Instituiton:Church)
2) EXISTS! x E marriages [ Husband(x, John) ^ Wife(x, Jane) ^
Institution(x, Church) ]

I'm sure you noted I tweaked FOL - the predicate instantiated in (1)
is unordered in that it includes attribute names rather than being
positional (which I think we'd all accede is in data modelling, where
attribute names are a vital part of the information being modelled).

Okay so my proposition in predicate form is a set of (attribute,
value) pairs. 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.

Ergo, in both (1) and (2) the marriage x can be described by exactly
the same construct... a set of (attribute, value) pairs!
This is the representation that underpins both, and I could infer /
either/ conceptual model, (1) or (2) from that underlying
representation. If I stick to that denotation I never have to
fractally dig down, reobjectify, reify, etc. We have one single
representation of the shared data from which someone may infer their
own particular perspective of the universe of discourse, objectifying
their hearts content to fit their particular application.

Entities and relationships. 2 subjective conceptual views of the same
underlying representation - a set of ordered pairs.

Surely QED? ... I await the rebuttals with interest ;-)
.

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