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Hi Chris -
Can you please send a pointer to your diagram for
CIM=Domain
PIM=Logical
PSM=Physical
I would like to build on this diagram for a map I'm making between the three
main classifications used in architecture (OmniClass,
Uniformat, and MasterFormat).
Would you say a parallel to your CIM/PIM/PSM diagram in the domain of
building architecture could be:
CIM = Domain = current resources including industry standards and test
methods, required drawing and specification formats, best practice
guidelines, laws and land records. In general, all information is from
"before" with the objective of not repeating mistakes while communicating
design intent and requirements clearly.
PIM = Logical = design formulas that can be followed to begin many different
types of projects (for example programming and flow diagrams to define
proximity and access for x numbers of people, certain levels of quality,
etc). In general, all is in eternal development.
PSM = Physical = actual buildings being used, both to achieve purposes inside
and their geographic locations, with more detailed information like local
building codes narrowing down the standards and formats above for specific
regions or use groups? Again, all elements already exist, even if only an
idea, an communicated idea in some form.
If so, it seems "accommodating
objects without identifiers" would
only be able to be handled in PIM = logic. Identifiers may not exist in the
domain yet because the design criteria for new or developing standards may
not have reached consensus yet. On the other end, there may be a limited
number of, or poorly executed, examples in the real
world. Logic would be the only area that is clean and uncluttered
enough to accept placeholders signifying possible objects. Because they have
no place to be "filed" or looked up in the domain, they may be lost
or torn to shreds on the front lines. In the real world innovations could
fail, or unusual designs may only be present for a short time only to be seen
or remembered by a few. The "missing pieces" may not need to
have an identifier in the logical realm, just a blank space held for future
contemplation and possible implementation based on the changing needs of one
or more domains or the real world.
Debbie
*************************************************
Deborah L. MacPherson
Specifier, WDG Architecture PLLC
Projects Director, Accuracy&Aesthetics
**************************************************
On 4/13/07,
Chris Partridge <mail@xxxxxxxxxxxxxxxxxx>
wrote:
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.
Regards,
Chris
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