Some comments below. Leo From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Matthew West
Sent: Tuesday, January 25, 2011 11:10 AM
To: '[ontolog-forum] '
Subject: Re: [ontolog-forum] Ontology of Rough Sets Dear Pat, You said: And I guess I have to defer to you when it comes to databases. But then I wonder why there has ever been a notion of, for example, a temporal database? After all, if database classes can change with time, why do we need to do anything special to make them 'temporal' ? There are at least two things going on here. Firstly, the whole point of databases is that you can add records to them. Of course as soon as you do, in principle you have a different ontology (or whatever you want to call it). However, that is OK, because what you want is an ontology of how things are now. [LEO:] Actually in the database world, one talks of the intensional database (the schema) and the extensional database (the rows/tuples). The closest equivalent to an ontology is the schema. With instances or facts being the rows. So the extension changes all the time, and one could even use the same schema for two different databases, which by definition have two different extensions. And though the schema does change over time, it doesn’t change often compared to the rows in tables. The idea of a temporal database is one where you not only know how things are now, but also how things were in the past, so you know about the changes that have happened as well as the current state, for example, a customer’s old address as well as their current one. There may also be other types of temporality, such as time indexed measurements. Regards Matthew West Information Junction Tel: +44 560 302 3685 Mobile: +44 750 3385279 Skype: dr.matthew.west matthew.west@xxxxxxxxxxxxxxxxxxxxxxxxx http://www.informationjunction.co.uk/ http://www.matthew-west.org.uk/ This email originates from Information Junction Ltd. Registered in England and Wales No. 6632177. Registered office: 2 Brookside, Meadow Way, Letchworth Garden City, Hertfordshire, SG6 3JE. From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Pat Hayes
Sent: 25 January 2011 08:04
To: [ontolog-forum]
Subject: Re: [ontolog-forum] Ontology of Rough Sets On Jan 22, 2011, at 8:58 PM, Christopher Menzel wrote: On Jan 22, 2011, at 6:47 PM, Pat Hayes wrote: On Jan 22, 2011, at 4:50 PM, Christopher Menzel wrote: ...A class can change its membership from one interpretation to another merely with the addition or removal of statements.
Sure.
i'm not sure I agree, and I wonder if Chris really does.
I don't. I hastily read Doug's claim to be the rather trivial claim that a class can change its membership from one interpretation to another by the addition or removal of elements from its extension. What does this even mean, "a class can change its membership from one interpretation to another" ? A given class NAME may be interpreted differently in different interpretations, of course: but the classes themselves - the entities, whatever they are, which are denoted by the class names and which are, therefore, classes - cannot "change ... membership from one interpretation to another" since they ARE entities in a given interpretation. It does not make sense to speak of 'moving' a class (or anything else) 'from' one interpretation 'to' another. I'm not following. Suppose I have a class name c in my language and let M be an OWL interpretation in which c denotes OWL class C. Now create a new interpretation M' that differs from M only in that we alter the extension that is assigned to c's denotation C. Doesn't that make credible sense of the idea that C's members have changed? I guess that does make a kind of sense, provided we are all agreed that we are talking within the Common Logic model theory. But it would not make sense if we were using classical Tarskian semantics or, for example, the OWL normative semantics. And I think it is a misleading way of speaking, since it is easily misunderstood as saying that one can take a set and change its members (and it still be the same set....) And even if it did, how would this be achieved by addition or removal of STATEMENTS? Classes do not (usually) contain statements. Agreed. That said, (2) does seem to be a strong *intuitive* idea in the KR, AI, and database communities.
This is the meaning i was referring to.
Never meant to suggest otherwise! :-)
Then allow me to suggest otherwise. As someone somewhat familiar with at least the KR and AI communities, I do not recall that the idea that class membership can change is, in fact, a strong intuitive idea there. If it were, the AI/KR field would have been happily using class language rather than, say, speaking of situations, ever since 1969. Temporal reasoners use many formal devices to represent time and change, but this simplistic notion of classes changing their membership is not one of them. If one were to try to use it in a realistic example, one would rapidly discover why.
I'll defer to you vis-á-vis the AI community; perhaps I've overgeneralized there. But in my own experience building "real world" database models and ontology models, I often heard folks talking about classes changing membership. Notably, in an implementation of a database model, intuitively, the instances of the classes identified in the model change with every update. And I guess I have to defer to you when it comes to databases. But then I wonder why there has ever been a notion of, for example, a temporal database? After all, if database classes can change with time, why do we need to do anything special to make them 'temporal' ?
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