Lecture 4: OntoClean

In this lecture, you will:

  • Learn how to theoretically evaluate ontologies
  • Learn about evaluation criteria
  • Learn how to correct ontologies
  • Learn that some modelling decisions are “more correct” than others



Assignment 2: Ontoclean



7 Responses to Lecture 4: OntoClean

  1. Julien L. says:

    I tried to realise a Mind Map while reading the very nice article! Might become quite helpful for understanding tomorrow’s class well or doing the 2nd assignment… 😉

    Here it is: https://dl.dropbox.com/u/61281858/OntoClean.png

  2. Robin says:

    We were working on the assignment today, and we were wondering if something could have identity but no unity, or the other way around?

    • Robin says:

      Our problem lies in misunderstanding identity, unity or both: We think of identity as being able to identify an instance of the class and thus tell them apart from other instances. Whereas we think of unity as being able to count all instances of a class. But if you are able to identify every instance, you can count them, and vice versa. Right? Well obviously not right, but where does it go wrong?

      • Julien L. says:

        I am far from being sure, but here is how I see it:

        You can tell water appart from fire, but you cannot count “waters”. You can count a quantity of water (in liters of cube meters for instance) but cannot say 1 water, 2 waters… Therefore I would say that water has identity (with an identity criteria which could be the H20 molecules and/or the liquid state…) but no unity (you cannot count waters).

        I can be wrong… :S

      • Julien L. says:

        Actually, after asking my friend Wikipedia (http://en.wikipedia.org/wiki/OntoClean#Identity), I would say that identity is more what you had in mind (tell individuals appart from each other within a class) more than what I was considering (tell individuals from different classes appart).

        So I would tend to agree that identity implies unity: if you have a way to tell to individuals appart (e.g. the passport number), the class has identity but you can then also count them (e.g. number of passengers) and the class therefore also has unity.

        It is then interesting to note that unity does not necessarily imply identity: you could be able to count individuals without having anyway telling the difference between them.

  3. Robin says:

    I’m not sure that you could. How would you know you’ve already counted someone, or that you haven’t counted him yet?

    • Julien L. says:

      I think that your way to see it is too practical. The question is more “in theory”, could you count individuals of that class. Like I’m almost sure that a class “Sheep” would have unity because you can count them. Even if in real life, counting sheeps is not an easy task since they all look the same, sheeps are a numerable notion.

      The question to ask yourself for unity, I believe, is more “is it numerable” than “is it easy to count without mistakes”.

      I made a little picture to illustrate my idea: https://dl.dropbox.com/u/61281858/red-circles.jpg Here you don’t need a way to tell the difference between each circle to be able to count them: you can organise the way you count, or even mark the ones you counted already, and agree with me that there are 10 red circles.

      Circles also have identity, since if you consider there center position, radius and color as an identity criteria you can actually tell the difference between each circle… but if in a given case, the class Circle did not consider the position as part of the identity criteria my 10 circles would actually all be the same circle and I would still consider Circle numerable and therefore having Unity.

      I couldn’t think about an example of a Class with no identity but with unity, though, so I might be missing something… After having a look at the assignment hierarchy, I noticed that the class Social Entity had no clear identity criteria and still had unity. Same goes for entites, since you can definitely count them but I couldn’t find a way to identify all entites from each other.

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