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.
where n,m are date-time expressions, for simplicity let us assume
integers representing milliseconds since some reference point.
Inn OWL 1.1 we can do quite a bit better - although again there is a
need for improved tools to make it easier.
* An organism has a given temperature at some point in an interval
anOrganism -->
has_feature SOME (Temperature_feature THAT
has_time_point SOME (has_coordinate SOME int[>=n, <m])
has_state...
* An organism has a given temperature throughout an interval. (This
has to be expressed as "Any temperature feature of the individual
anOrganism in the time interval has the given state"
Temperature_feature THAT
is_had_by VALUE anOrganism AND
has_time_point (Some has_coordinate SOME int[>=n, <m]) -->
has_state...
where is_time_point_of: inverse has_time_point
has_time_point: functional
Axiom: (Feature THAT has_time_point SOME Time_point) has_value Max
1 State.
has_coordinate is used here with int since I am assuming it is
measured in "ticks since basepoint", but could equally well be a float
Nevertheless the results are clunky and will need special tool
support[**] to avoid going insane. In general I am wary of design
pattern type things - they are usually a sign that the language
lacks the constructs required to express things unambiguously and
concisely.
Separate "unambiguously" and "concisely". Whether or not there is
something ambiguous about a design pattern depends on the case. In
this case I think there is no ambiguity. "Concisely" is a matter for
tools and layered "higher level languages".
The history of computing is the history of "design patterns" at one
level that eventually get built into "higher level languages" at the
next level of abstraction up. No one would argue against layoring
more convenient languages on top of OWL ( or its successors). The
patterns are a first step towards this end, just as they were in the
early days of programming languages. Neither would anyone argue
against more expressive languages.
But I would argue that building on known, tested, and proven
semantics and computational methods is preferable to inventing new
ones. I'd rather spend my time on improving tooling for something
well-understood, standardised, and supported by a community of
specialists than on trying to invent something new on my own that was
likely to be none of these things. I'll invent when I have to -
when I am convinced that the best available methods do not meet
mission critical needs. But I take a lot of convincing, and even if
convinced I will build out from the well understood foundations
wherever possible, with just enough extra invention to do what is
required.
I speak from experience. I've done both.
Regards
Alan
-----------------------
Alan Rector
Professor of Medical Informatics
School of Computer Science
University of Manchester
Manchester M13 9PL, UK
TEL +44 (0) 161 275 6149/6188
FAX +44 (0) 161 275 6204
www.cs.man.ac.uk/mig
www.clinical-esciences.org
www.co-ode.org
