On 21 May 2007, at 19:50, Chris Mungall wrote:
On May 20, 2007, at 11:49 PM, Alan Rector wrote:
Chris
On 18 May 2007, at 18:10, Chris Mungall wrote:
I'm afraid I'm unclear how to state the OWL n-ary relation
pattern(http://www.w3.org/TR/swbp-n-aryRelations) where I really
need it. In all the examples given, the "lifted"[*] n-ary
relation was never truly a relation in the first place and always
better modeled as a class. It's kind of cheating. What if my
n-ary relation is transitive or if the 3rd argument is a temporal
interval over which the relation holds?
I think the former is doable with property role chains. Updating
the n-ary relations note with this - and all the other omitted
details, such as how to re-represent domain/range, functional
properties, n-ary relations in restrictions etc - would take a
lot of work and would make it utterly terrifying to the naive
user.
Nevertheless the results are clunky and will need special tool
support[**] to avoid going insane.
I'd love to see DLR or similar means worked into future versions
of OWL or other standards, although I am not the one to comment on
the logical/complexity issues. I certainly agree that
re-expresssing relations as properties carries a modest penalty by
being more verbose, but it is manageable.
To take the example in question for some relation R, let's take
temperature as an example. I shall use the subrelations
"has_feature" / "has_state" to minimise arguments over what is,
and is not a "quality" - an issue not germane to this discussion.
Also I will use "has_state" as the property name so we don't have
both a property "has_value" and a keyword VALUE.
In the binary relation form in manchester simplfied syntax in OWL
1.0 we have:
Organism has_feature SOME (Temperature_Feature THAT
has_temporal_extent VALUE temporal_extent_1 AND
has_state SOME (has_magnitude VALUE 37 AND has_units VALUE
degrees_C))
where temporal_extent_1 is an individual which has facts
has_start_time VALUE n AND has_end_time VALUE m.
has_magnitude is a functional datatype property and has_units
is a functional property.
For the record, I accidentally left this ambiguous as to whether it was
"Organisms that a temperature of 37C during temopral extent 1"
Organism THAT has_feature. SOME (...
or the claim, better as
"This class of organism has the temperature feature during temporal extent 1"
"ThisOrganismClass --> has_feature SOME (...
Should be
Here Temperature_Feature is a "history" (sensu Hayes) or a
time-slice. Do I have this correct?
Deliberately left ambiguous to limit the number of cardinaltiy
constraints to explain. It depends on the cardinality of
is_feature_of. I had not put a max 1 cardinality constraint on it,
implying that there can be many features, but any feature at any
time. For most purposes the inferences are the same. However, to
expand the example.
If you want features to be 4-D objects
Just for the record, that IS the 'histories' view. That is,
'histories' was the name I used for 4-d objects.
that have values at a time,
However, 4-d objects don't have values *at a time*, since they have
time built into them. They are objects-at-a-time, and they simply
have values. If they weren't objects-at-a-time, they wouldn't be 4-d.
Let's go back to basics.
What is the statement in plane English? I presume:
"A protein that is located in some cytoplasm during some temporal extent"
What inferences do you want to draw about the Protein? the Cytoplasm?
As usual with a robust call to plain old English, it is no longer
clear what we are talking about. What ARE these entities?
Continuants? Occurrents? Do they extend through time? Do they have
temporal parts? Do they have spatial parts?
the History of each?
In the 4-d view, these things (in fact, everything that exists in
space-time) IS a history. Histories do not 'have' histories. (The
idea of a thing having a history, and the two of them being
inherently distinct, is a hallmark of the continuants notion, where
continuants aren't allowed to have temporal parts. Unfortunately,
this continuant/occurrent distinction has been welded into BOF and
DOLCE and so has become very influential.)
What inferences do you wish to make that you cannot make from the
simpler representations?
What else do you need to say that can be expressed with Histories
that cannot be expressed in the simpler representation?
Seems to me that histories is a simpler representation. It treats all
spatiotemporal entities uniformly, and does not require maintaining a
distinction between continuant things and occurrent
lifetimes-of-things, for example. All it amounts to in practice is to
be rigorous about the idea that (expressed in terms familiar to
occurrent/continuant philosophy) everything is an occurrent, so
everything has temporal parts. Even continuants are occurrents :-)
Temporal parts can then be simply related to one another without
being concerned with where to put the temporal parameters, etc.. So
in this example, the relation between the protein-during-extent and
the cytoplasm-during-extent (both temporal parts of protein and
cytoplasm, respectively) is simply located-in, with no temporal
qualification at all. Since all part-of relations, temporal or
spatial, are binary, this fits very well into the OWL world of binary
properties. One way to do it for example is to treat a time-interval
as a property on things whose value is the relevant temporal part of
that thing. Of course, this isn't how we speak in English, which is
no doubt why many people find it confusing at first; but one can
treat this simply as a matter of translation of surface form. To say
that (say) A is inside B during interval I, is a compact way of
saying A-I is inside B-I; or using the convention suggested above,
that the I-value of A is inside the I-value of B. Humans prefer the
more compact representation, which is fine. But what best fits the
human left temporal lobe is not necessarily best for machines to
reason with. And in any case, as I myself can attest, it does not
take long to get used to the 4-d way of thinking. Assuming of course
that I am human.
Pat
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