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Re: [ontolog-forum] Ontology, Information Models and the 'Real World'

To: "'[ontolog-forum] '" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: "Chris Partridge" <mail@xxxxxxxxxxxxxxxxxx>
Date: Fri, 13 Apr 2007 14:26:24 +0100
Message-id: <00f801c77dcf$55d62bb0$6f00a8c0@Aegir>

Hi Ed,


Just to say before I get to the discussion/questions - I really liked your seminar. I especially liked your listing and analysis of the functionality required for information models. We need more of this.


I think we were asked to continue our discussion on this forum.


The point I started to raise (and we started to discuss) in the forum was where the ‘real world’, things or entities entered into the equation.


You mentioned Peter Chen and the distinction he made between modelling things and the information about things – which (as you said) shows this has been a concern for some time.


What I felt was that your exposition of information modelling (as is often the case) seemed to me to dance between these two interpretations. Let me try and justify my claim.


For example:


EB>”Entity type classifies things in the universe

Value type classifies information about things

Data type represents Value types”


Line one seems to be discussing the domain, whereas line two deals with information.


It is clear that there is a strong strand through the development of information modelling of the need to model the domain (the universe of discourse).

There is also a clear distinction between a logical system model and physical system model, where the logical model does not concern it self with the particular physical platform.


I think OMG’s MDA structure is a useful framework to illustrate this point. One can see the CIM as the model of the domain, the PIM as the logical model and the PSM as the physical model. I have a diagram of this if anyone wants.


What seems to me to have happened back in the 70’s and 80’s (and I am publishing a paper on this) is that the business domain model and the logical system model have been (deliberately?) confused. One reason, I think, is that there is an assumption that the same model can be seamlessly interpreted in two ways. Another reason is the lack of a framework for explaining/understanding the structure of the domain (and so its model) and how this is translated into information.


How does the confusion arise? Firstly, I think there is a problem with the terms. One would expect an ‘information model’ to be a model (in the engineering sense) of the information – rather than a model of the domain referred to by the information.


EB>“Information models

universe is things used by the business processes

classification/axioms are as used by the business
business rules, not accepted scientific truth

distinguish conceptual schema
            = invariants, quantified assertions
from the information base
            = current assertions about individual things “


Similarly, one would expect that ‘conceptual schema’ and ‘information base’ to be at one remove from the domain/real world – in the information world.


There also seems to a divide between academics and practitioners, where the academics focus on the information model and its structure, whereas practitioners worry more about how the ‘real world’ is reflected in the domain.


What seems to me to be opportunity open to ontology is to build on the requirement these practitioners are raising – for a model of the domain.


A modern definition of ontology ("the set of things whose existence is acknowledged by a particular theory or system of thought." (E. J. Lowe, The Oxford Companion to Philosophy) ) seems suited – and one can go back to 1967 (Mealy) to find this being recognised.


However, the computer science favoured definition of ontology (Gruber’s “specification of a conceptualization”) seems more to focus on information/concepts than the domain.


From what you said in the seminar, it would seem you look favourably on ‘real world’ models.


However, I think the information modelling community is so tied into looking at information, it often misses the domain.


I would like to, if I may, take an example from your slides.


You talked about identifiers – and gave a v. useful overview on how they are used in information models/systems.

However, it seems to me that not enough attention is being paid to the ‘real world’ here.


Before, I explain, let me make clear that I am not talking here about the (internal) identifiers that systems need to maintain to keep track of items. These seem to me to sit within the information world, rather than the universe of discourse.


EB>“Identifiers/keys distinguish instances of an entity class

simple key: a property whose inverse is “functional”

for each v in the range, there exists at most 1 d in the domain
such that P(d,v)

almost always an attribute (value type)”


What I understood you to be saying is that things should have identifiers.

While this is a practical issue for the information system, it is not true that these exist in the real world. Something have identifiers – some don’t. Some have multiple identifiers. Etc.

What is more interesting to me is what kind of thing names/identifiers are. I do not see much investigation of this in the information modelling community.


So, the thrust of my argument goes like this. If we are modelling the domain, we need to look at the domain.

Is it true that every object in every domain has an identifier? I think not, so we need to accommodate objects without identifiers.

Do identifiers exist in the domain? I think so.

If they do, do we know what they are? I think it is not clear that we do.


I suspect this is enough to get our discussion going.








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