Dear Mike, (01)
Alas, everything is abstract except the members of particular_quantity. The
different abstractions are at different meta-levels, which it is why it is
so confusing. (02)
I have taken Hajo's example, and shown the objects and their meta-levels in
http://www.caesarsystems.co.uk/uom_ontology_progress/uom_ontology_progress-f
iles/quantity_meta-levels.gif . (03)
The bottom left of the diagram has exactly what Hajo wishes. The top right
of the diagram is entirely abstract and may seem unnecessary, but I do not
think that this is so. Its utility is justified as follows: (04)
1) "1.3 metres" and "the metre" are both members of "magnitude of quantity"
and of "length as a class of magnitude" (neither are members of "length as a
class of particular quantity" because both are abstractions and not members
of "particular quantity");
2) that "1.3 metres" can be expressed in terms of its relationship with a
unit, such as "the metre", is a property of the class "length as a class of
magnitude";
3) a subclass of "Q4, kind of quantity as class of magnitude" can be defined
that contains all members for which a simple relationship with a unit exists. (05)
Best regards,
David (06)
At 00:39 05/09/2009 +0100, you wrote:
>Would it be less confusing if one of those had a parent class of
>"Abstract Thing" and the other had a parent class of " Concrete thing"
>or "Particular thing" or some such? Because I think you've hit the nail
>on the head about what the actual distinction is, and therefore it
>should be possible to represent that in the upper ontology.
>
>More broadly, all these distinctions would surely lend themselves to
>modeling such that the model, and not the reader's understanding of some
>paragraph, is what captures or fixes the meaning?
>
>Mike
>
>Ed Barkmeyer wrote:
>> Rijgersberg, Hajo wrote:
>>
>>> 1. Maybe the most important question is (and probably only for my
information and understanding): why do we base the vocabulary on VIM?
>>>
>> VIM is the International Vocabulary for Measurement, a publication of
>> BIPM -- the people who maintain the international standards for units of
>> measure. http://www.bipm.org/en/publications/guides/vim.html
>> It seemed like adopting their vocabulary would be good, and we have
>> tried to stay close to that.
>>
>>
>>> (I'm very interested in studying VIM, but couldn't find the document.
Could someone please send me a link?) There are also other documents that we
could base our vocabulary on.
>>>
>>>
>> Yes. For example, we could use the model in DOLCE or Cyc or SUMO or
>> some other published upper ontology that provides formal axioms for the
>> quantity and measurement concepts. We have a work item that says we
>> should look at these.
>>
>>
>>> 2. But then I ignore VIM, and repeat myself: couldn't we have:
>>>
>>> "length of my table" ---"member of" ---> "length quantity"
>>> "length quantity" ---"subclass of" ---> "quantity"
>>>
>>> This is in accordance with some standard documents I know.
>>>
>>>
>> And it is in accordance with the model that David has produced. But he
>> uses "instance of", instead of "member of" ("instance" is an
>> "intensional" characterization; "member" is an "extensional"
>> characterization; although probably only an ontology purist would care.)
>>
>>
>>>
>>> 3. Also, according to these documents, e.g. "1.3 metre" is not a
quantity, but a measure.
>>>
>> Agreed. VIM calls it a "quantity value", which is an "expression of the
>> magnitude of a quantity". VIM uses "measure" to talk about a process
>> for determining a quantity value and for the results of that process.
>>
>>
>>> (A quantity is like a variable, it is a reference to a value, like "1.3
metre".)
>>>
>>>
>> We are careful to distinguish the class "quantity", whose instances are
>> particular quantities, like "the length of your table", from the class
>> "quantity magnitude", whose instances are the abstractions -- amounts of
>> length stuff. So if you have two chairs next to your table and they are
>> identical in size and shape, "the height of the first chair" is a
>> (particular) quantity, and "the height of the second chair" is a
>> (particular) quantity, and they are _different_ instances of "quantity",
>> but they have the same "magnitude". That is, there is one amount of
>> 'length' that they both have.
>>
>> "1.3 metre" is a quantity value, which is an expression/name for a
>> "quantity magnitude". If your chairs are 1.3 metres high, then "1.3
>> metres" is a name for the magnitude of the height of each chair. And of
>> course, the same magnitude can have other names, such as "51 inches".
>> "51 inches" and "1.3 metres" are two different quantity values, but they
>> express the same "magnitude". That is the model we are proposing.
>>
>> But then there are two (or more) different classifiers that are called
>> "length". length-1 is a subclass of "(particular) quantity". The
>> length of your table is a length-1, the height of the second chair is a
>> length-1. But the magnitude of the height of the second chair is not a
>> length-1. length-2 is a subclass of 'quantity magnitude'. The
>> magnitude of the height of the second chair, which is the same as the
>> magnitude of the height of the first chair, is a length-2. So we must
>> choose one of these to be what we mean by "length". VIM is very clear
>> that it means length-1. But then we must not say that "1.3 metres
>> expresses a length"; we must say (as VIM does) that "1.3 metres
>> expresses the magnitude of a length".
>>
>> I personally think this usage is confusing for everyone. I would prefer
>> that we use "particular quantity" to be the class of things like the
>> height of the second chair, and use "quantity" to be what VIM calls the
>> "magnitude". But, on the other hand, you can't ever measure a
>> "magnitude"; you can only measure a particular quantity -- the height of
>> the second chair. The "magnitude" itself is not a physical phenomenon;
>> it is an abstraction. So it is very important that we agree on what
>> definition we choose for each term we use. Otherwise, everyone is confused.
>>
>>
>>> Again, hopefully this discussion is appreciated; it is meant to be
constructive, with the aim of working together to achieve a high-quality
vocabulary.
>>>
>> Me, too. But we keep going around these same issues, because people
>> don't understand the definitions.
>>
>> -Ed
>>
>>
>
>
>--
>Mike Bennett
>Director
>Hypercube Ltd.
>89 Worship Street
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>
>
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> (07)
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