On 30 Jan 2014, at 08:38, Matthew West wrote: Dear Andrea, Actually, over constrained axioms (or their application to over general terms) is one of the main reasons for a lack of reuse. I once came across a data model that had as a constraint that an oil company only had one refinery. Guess how reusable that was… It is the embedding of local constraints that might be true locally (and accidentally) but are not true generally that is the biggest barrier I have found to reuse. So when you come across such a data model or ontology, in attempting to reuse it, you inevitably have to generalize (which usually means removing inappropriate constraints). There is no need to apologise for this. Of course, it is then OK to specialize and add constraints that apply to the specialization, which is your local set of constraints. Just don’t make the same mistake as those before you.
I led a group in an unnamed ISO committee on the architecture for modularizing a suite of large information models. There were lots of lessons learned but a few key ones were:
1 - the optimal breakdown of an ontology into modules is different depending on whether you are the creator or user of the ontology. The mistake the ISO committee made was that it only ever thought about reuse from the point of view of the standards-maker, what was important for the implementors of that standard was an afterthought and the process and modeling language made supporting that different viewpoint nearly impossible.
2 - maintain modular layers of structure and usage rules separately. All organizations, disciplines and industries have many rules wrt the creation of usage of data, and all organizations, disciplines and industries break those rules regularly ... real life is too complex to model correctly in the time/money available, so there are always exceptions.
3 - no set of ontologies is ever sufficient. Organizations and industries will always need to extend, modify or replace portions of the beautifully modular ontology that you create.
4 - build a plan for change into your process. Needless to say the ISO committee was beyond hopeless in this respect (i.e. mistakes made 20 years ago are treated as gospel, even today). Obviously, change is more acceptable in some industries than in other. A friend working in telecoms and was always asking how we could be using "engineering standards" that were 5 or 10 or 15 years old - in telecoms everyone expected change every year or two.
A couple of personal thoughts on this wrt OWL:
- OWL enables reasonable solutions to 2 and 3 above.
- don't make your approach to modularity/reuse depend on inferences such as sameAs for any app where scalability is a requirement. Simple rdfs:subClassOf and similar inference is fine over the "schema", but don't depend on anything that infers over the "data" ... just too many performance/scalability issues. I realize others have suggested this approach, and it may work in some scenarios, but it does not work in large-scale data integration scenarios for example. I also realize the linked data world is built around sameAs, which seems to me to be an issue to address wrt reuse of linked data in a large-scale app (unless the linked data in question has followed rule 2 above:-).
- WRT 1 and 4 (and 3 as well), a better approach than producing "complete" ontologies is probably to produce a library of small, self-consistent, reusable "ontology snippets" and let organizations, disciplines and industries build what they actually implement using those as a basis. That library could also include software that interacts with those ontology snipptes (e.g. present an instance of this class in a Web page or as JSON-LD). I guess this is really a functional "parts catalogue" for ontologies.
Mike raises a good point wrt the purpose of the ontology, and this is something the OMG UML and things like UPDM/DODAF/MODAF support reasonably well. However, there seems to be little in the way of support in the semantics world for identifying the role/purpose of the ontology in a larger architecture framework of ontology. For example, I've even resorted to crazy things like subclassing OWL Ontology to provide some hint wrt the purpose of an ontology in an overall ontology architecture framework. FWIW we subclass OWL Class regularly too:-)
Cheers, David
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Regards Matthew West Information Junction Mobile: +44 750 3385279 Skype: dr.matthew.west This email originates from Information Junction Ltd. Registered in England and Wales No. 6632177. Registered office: 8 Ennismore Close, Letchworth Garden City, Hertfordshire, SG6 2SU. From: ontology-summit-bounces@xxxxxxxxxxxxxxxx [mailto:ontology-summit-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Andrea Westerinen
Sent: 30 January 2014 02:23
To: Ontology Summit 2014 discussion
Subject: Re: [ontology-summit] [Reusable Content] Characterizing or measuring reuse Ed, Thanks for the clarification. I would agree with you regarding the concept of consistency as defined by axioms. However, I was also advocating for 1) more modularity (as you point out) and 2) separation (from the entity declarations) and acknowledgement of the axioms. In this way, there is the possibility for the axioms to be reused (or not) or evolved. To be clear, I am not saying that simply splitting the axioms from the entity declarations is sufficient to mend a basic difference in semantics and allow reuse where it is not reasonable. But, it may be sufficient to overcome minor contradictions by defining different but still semantically relevant axioms. Thanks for continuing the dialog to clarify and tease apart the concepts ... Andrea, When I said “consistent”, I meant it in the formal logic sense:. If I propose all the axioms in the two theories, I cannot infer a contradiction. Now, I may import an ontology that describes a single general concept and has many subclasses and properties that I can use, and other aspects I don’t care about. It is very unlikely that incorporating that ontology will produce inconsistencies, as long as I agree with the statements about the elements I intend to reuse. But consider, for example, the case in which I import an ontology for time. It will have a very small number of undefined terms with characterizing axioms, and quite possibly a rather large set of well-defined terms for derived concepts, some of which I use. Again, I can see pretty clearly whether the parts I use are consistent. But suppose the time ontology says that a time interval can be started by an event, and it provides a number of axioms that characterize its “event” notion. In my ontology, I want to use that idea, but I have an elaborate model of events and activities. Now I need to be sure that the imported axioms for ‘events’ (or whatever symbol I equate) don’t contradict my axioms, directly or indirectly. If there is a contradiction, we don’t mean the same thing by “event”. I can still use the imported ontology if I have some class that satisfies the imported event axioms (a “mapping”), but the import is only useful if I agree that that, or some subclass of it, is the class of things I want to use as the start of time intervals. Further, if my intended use is a subclass of the imported “event” concept, I need to know that admitting instances of the imported class that I don’t intend to use as the starts of time intervals won’t contradict something I say about activities and time. In particular, consider the case where the imported ontology says that every event starts the time interval in which that event “has happened”, and implicitly all subintervals thereof that start at the same instant. If his ‘event’ includes things that my model says have a non-zero duration, and I consider those ‘events’ not to “have happened” until that duration has elapsed, there are some small intervals in which the imported model says the event ‘has happened’, but my model says the event ‘has not happened’ but ‘is happening’, which is a different state. Then there exist events e and time intervals t in which my theory says (not (hasHappenedin e t)) and the imported ontology says (hasHappenedin e t), which is a contradiction. There is clearly an underlying inconsistency in intent, but it is only a logical inconsistency if I care about the specific behaviors of things that are accidentally included in his somewhat larger category. This is a version of Pat Hayes’ “Horatio principle” – “there are more things in (my) heaven and earth, Horatio, than are dreamt of in your philosophy” (Hamlet, Act I). As Gary (?) pointed out, this is why you would really want these ontologies to be as modular as possible. If the imported ontology for “events and time” includes, but is separate from, the imported ontology for “time”, I can import the latter without creating the problems engendered by importing the former, even if I really wanted the kind of thing the former covers, and have to develop that part separately. And it would be a different kind of “reuse” if in that ‘separate development’ I take his “events and time” ontology and MODIFY it to be consistent with my events and activities module. I think this latter is a pretty common form of ‘reuse’. (I am reminded of Tom Lehrer: “Don’t let others’ work evade your eyes, ... but plagiarize, plagiarize, plagiarize (only be sure always to call it, please, ‘research’).”* J) -Ed * from “Lobachevsky”, Tom Lehrer, 1960.
To: Ontology Summit 2014 discussion
Subject: Re: [ontology-summit] [Reusable Content] Characterizing or measuring reuse Gary and Ed, There are two bullets in the reuse discussion where I (somewhat) disagree ... - the content is consistent with the micro-theory adopted by the re-user - the re-user is able to determine that the content is consistent with his/her theory Yes, I guess that we might look for structural consistency which was perhaps handled in the conversion process mentioned previously, the logical consistency (check with a reasoner?) and consistency with the user's conceptualization.
I don't think that the content must be consistent, but the content must be mappable or translatable.
This takes us back to Hans' point about understanding the assumptions and context of the original content ... Just as more discussion showed that the events in Pascal's talk and in FIBO were semantically close (if not equivalent), it is important to somehow enable a similar line of reasoning. We need to understand how and why some model was created/defined as it was, and then other alternatives/possibilities that the model enables. The problem here (as Cory noted) is time and money to create the information or have the dialog. Is this something that could be crowd-sourced?
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