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Re: OMG Ontology Metamodel Definition Review

From: Phil Tetlow <philip.tetlow@uk.ibm.com>
Date: Wed, 26 Jan 2005 10:50:27 -0500
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Cc: Christopher Welty <welty@us.ibm.com>, public-swbp-wg@w3.org, ewallace@cme.nist.gov, Grady Booch <gbooch@us.ibm.com>, Bob Lojek <bob.lojek@uk.ibm.com>
Message-ID: <OF053BCBDC.C89739EF-ON80256F95.0055A4A0-85256F95.0055DDFA@uk.ibm.com>


Certainly. My recollection of the last telecon was that Guus asked for a
personal review of the ODM document and, as such, I tried hard to phrase my
mail from a first person perspective. The text below, as you quite
correctly identified, is, hence, solely a collection of personal thoughts
and in no way represents IBM's corporate opinion. If a corporate opinion is
required then this will take significantly more time and effort.
Nevertheless I did pass my review by Bob Lojek for comment before I
submitted to the public mailing list . As such I have also copied him on
this mail as well.

Kind Regards

Phil Tetlow
Senior Consultant
IBM Business Consulting Services
Mobile. (+44) 7740 923328

             Jeremy Carroll                                                
             com>                                                       To 
             Sent by:                  Phil Tetlow/UK/IBM@IBMGB,           
             public-swbp-wg-re         Christopher Welty                   
             quest@w3.org              <welty@us.ibm.com>                  
             26/01/2005 10:09          ewallace@cme.nist.gov, Grady Booch  
                                       Re: OMG Ontology Metamodel          
                                       Definition Review                   

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.



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)
> 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
> 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
> 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
> 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
> or the introduction of completely new schematic representations then so
> it. Most agree that graphical ontology conceptualisation needs to be
> 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
> 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
> indeed may well cause barriers to successful ontology modelling.
> Nevertheless such problems have been encountered a number of times
> 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
> 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
> 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
> 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
> to be pragmatic, rather than academic, and allow the UML to maintain the
> upper hand? Surely only the most adventurous gamblers amongst us would
> 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
> 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
> 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
> 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 15:46:58 UTC

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