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Re: OMG Ontology Metamodel Definition Review

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Wed, 26 Jan 2005 15:09:08 +0000
Message-ID: <41F7B294.8040604@hplb.hpl.hp.com>
To: Phil Tetlow <philip.tetlow@uk.ibm.com>, Christopher Welty <welty@us.ibm.com>
CC: public-swbp-wg@w3.org, ewallace@cme.nist.gov, Grady Booch <gbooch@us.ibm.com>


Phil, Chris,

I would find it helpful if you could clairfy whether this review, 
particularly the paragraph "So my preference would not be to construct 
the ODM as ‘an aggregate ..." is a personal comment (as the language 
suggests) or a comment with IBM support.

thanks

Jeremy


Phil Tetlow wrote:
> 
> 
> 
> I have now provisionally reviewed most of the OMG’s Ontology Definition
> Metamodel (ODM) document and on first reading consider section 14 (ER
> Metamodel) to be a recognised subset of the UML which, as such, does not
> warrant significant comment. Bob Lojek (IBM) has also kindly reviewed
> section 10 (UML2 Metamodel) and his findings are appended at the end of
> this mail.
> 
> Firstly I must state that I consider the ODM paper to be a broad and
> significant embodiment of current thinking on the representation of
> ontologies. It extensively collates and articulates a number of
> perspectives that are of great value and I especially like the material
> presented in section 7 (Usage Scenarios and Goals). I find, however, the
> material presented in section 8 (Design Rationale) and 9 (ODM Overview) to
> be somewhat misdirected.
> 
> Section 8.2 presents reasoning as to why the ODM cannot be fully
> represented in the UML, specifically stating a number of acknowledged
> weaknesses within the language. Nevertheless I think that this is being
> somewhat unfair and one must remember two important points about the UML as
> a descriptive tool:
> 
> o     Firstly a primary purpose of the UML is ‘U’nification. This, by
> definition means that it has to cover a lot of ground, hence loosing out on
> specialisation in some cases in favour of a deliberately generalised
> approach. The paper acknowledges this fact but does not appear to convey
> the true values behind a unified approach to modelling.
> o     Secondly the UML is a living ‘L’anguage and as such it should be
> viewed as an evolving entity in its own right,  capable of change to meet
> the requirements of most of the new, valid contexts in which it might be
> used. Just because the UML 2 does not natively support specific concepts
> required for the accurate representation of certain types of ontology does
> not mean that it should or will not in the future. Perhaps, therefore, it
> should be job of this Working Group to recommend amendments for inclusion
> in later versions of the UML. If this means wholesale architectural changes
> or the introduction of completely new schematic representations then so be
> it. Most agree that graphical ontology conceptualisation needs to be based
> closely around a Direct Graph theme and even if either Profiling or
> Stereotyping cannot accomplish this directly in the UML 2 for more
> specialised ontologies, the mapping of predicate associations is central to
> its ethos and culture of those who use it professionally for whatever
> purpose as part of their daily practices. Adding more types of graphing
> schemes to cope for formal and specialised ontology representation is
> hardly going to be rejected out of hand.
> 
> Nevertheless, I agree in particular that there are problems with cross
> meta-level representation in the UML as it currently stands and that these
> indeed may well cause barriers to successful ontology modelling.
> Nevertheless such problems have been encountered a number of times already
> in the modelling community and the use of proper and structured object
> referencing mechanisms has traditionally surmounted such problems.
> Admittedly this adds a layer of complexity on top of any raw ontology
> itself, but that is the nature of the beast – formal representation often
> needs additional ‘straight jackets’ to accommodate more specialised ways of
> thinking.
> 
> So my preference would not be to construct the ODM as ‘an aggregate of
> equal and independent metamodels’ (as described and illustrated in 8.4 and
> 9.0). Instead I think that a ‘hub and spoke’ based model would be more
> valuable, with the UML acting as the hub. Where features of the five
> remaining metamodels cannot be represented directly, then emphasis should
> be placed on either constructing new UML mechanisms for direct
> representation or establishing suitable compromises and translations for
> the purpose of unification. The reasoning behind this approach comes purely
> form the huge gains that unification brings and not out of any preference
> for the UML as a descriptive medium. ‘Pick your poison then drink’ should
> be the message, so long as everyone drinks the same poison. Then at least
> we can all meet in hell afterwards and compare notes, right?!
> 
> From my point of view the UML, for all its faults, has proved its worth
> many times over in the hard faced commercial reality that is significant
> systems’ development. The same is not yet true of ontology representation
> and embodiment, yet its potential is plainly apparent to all who take the
> time to investigate properly. If, as I suspect we all agree, we want to
> make the power of knowledge representation, through graphical ontology
> modelling, available to a much wider audience, then perhaps now is the time
> to be pragmatic, rather than academic, and allow the UML to maintain the
> upper hand? Surely only the most adventurous gamblers amongst us would not
> admit that, for now, the UML is safest ‘bet in town’.
> 
> -----------------------------------------------------------------------------------------------------------
> -
> 
> Bob Lojek wrote:
> 
> Phil,
> 
> Here are my comments:
> 
> Talk to you tomorrow
> 
> Cheers, Bob
> 
> 
> The approach has 4 levels of abstraction called metalevels,
> 
> M0, M1, M2 and M3; each is increasingly abstract as Mn increases and
> decomposable in the opposite direction.
> 
> 
> 10.2.1 UML Kernel
> ---------------------------
> 
> Page 64: "There is no direct linkage between Association and Class. The
> linkage is mediated by Property."
> 
> In the M1 model, why are association stereotypes not used, although table
> 11 and 12 indicate they are?
> 
> 
> 10.2.2 Class and Property - Basics
> --------------------------------------------------
> 
> Page 67: "That is there are cases in which a relational database
> implementation would use a
> compound key to identify an instance of a class."
> 
> This is a conditional association, for example a foreign key that points to
> several primary keys depending on runtime values. Shouldn't this be
> described a the M0 level?
> 
> 
> In the example
> 
> (Embedded image moved to file: pic04092.jpg)
> 
> I would stereotype the association as <<enrolled>>  and perpaps the
> property as well. This will make it easier to process to downstream
> systems.
> 
> Also the relationship of grade to enrolled is unclear to me, looking at the
> diagram and this table.
> 
> 
> (Embedded image moved to file: pic16522.jpg)
> 
> 
> 
> 10.2.3 More Advanced Concepts
> 
> How will namespaces be addressed in the UML model? We are, for example,
> using packages.
> 
> 
> This is basically a comparison between OWL and UML 2, why not go back to
> the language definition of OWL and map the coressponding UML equivilants to
> it. This was done in "Table 18 Common Features of UML and OWL" but in the
> opposite direction.
> 
> Regards
> 
> Phil Tetlow
> Senior Consultant
> IBM Business Consulting Services
> Mobile. (+44) 7740 923328
> 
> 
> ------------------------------------------------------------------------
> 
> 
> ------------------------------------------------------------------------
> 
Received on Wednesday, 26 January 2005 15:10:19 GMT

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