Tuesday, February 14, 2006
Generative Methodology Glass Bead Games
n-articulated ontological framework
On using RDF to model web services
Link back to part of the “solution” to translations between
RDF / OWL and Models of Information -> [167]
Sub-theme
n-articulated
ontological framework
[168] [169] [170] [171] [172] [173] [174]
Communication to the Protégé forum from Andrea
Hi Dirk,
UML was intentionally designed without an unambiguous formal semantics, and after 8 years it still does not have one: indeed, UML is defined by means of itself, i.e. it is specified by its metamodel, which in turn is expressed in UML.
This reflects a precise conscious design decision not to give it a formal semantics. I do not say that this is necessarily bad, but just that it is a strong point of criticism; anyway, I am really glad to hear that someone is eventually working on that. As long as no formal, standard, and agreed-upon specification of its semantics is given, however, UML remains a mere graphical notation. As to the "expressiveness" issue, no quantification of "expressiveness" is possible unless a formal framework that denotes *what* exactly a UML model expresses, and how relationships, classes, and objects exactly relate to one another, is provided.
The reason why you perceive that the instance-of relationship is overused and you suggest to replace it with is-role-of properties, in my opinion, is not that you don't really need the semantics of the instance-of relationship, but that you want instance-of relationships to behave like is-role-of properties in ordinary programs, i.e. being able to change dynamically and possibly assume several values.
This is probably due to the fact that you are deeply involved in the Software Engineering discipline, and I can understand your point of view because I also was a few time ago. But still, replacing instance-of with is-role-of properties is just a trick, an implementation issue that arises. You have already made a commitment to the execution platform (the logical model) in which you are going to translate your conceptual models: that of an object-oriented programming language.
Actually, I conjecture that , you don't want to give up the semantics of instance-of, you just want to overcome the limitations that are imposed by those environments because they designed to maximize efficiency.
Please note, that I am not claiming that object-oriented programming languages are something "improper", just that they have very specific goals, and "expressive" conceptual modeling languages should have a denotation, set-based, model-theoretic semantics in order to be regarded as such. And this applies to UML, if its expectations include, as you say, not to be just a graphical notation.
Anyway, Dirk, in case you felt my post was rude or offending, I apologize for that: don't feel attacked. I was only trying to expose my point of view; maybe I did it with too much strength. ;)
Friendly,
Andrea