From: pat hayes ([email protected])
Date: 04/24/01
Checking thru the walk-thru. The section which introduces properties
is worded in a way that suggests a different semantics from the one
given in the model theory.
The example says that the domain of hasParent is #Animal, and this
clearly suggests that the intention is that this should mean that
every animal has a parent, ie that hasParent applies to the entire
domain class (in contrast to the range specification.) I wrote the
following 'explanation' before realising that it might not be true:
"The range specification restricts the property from 'above', ie it
specifies a class into which the value of the property must fit,
while the domain restricts it from 'below', ie it specifies a class
which must be included in the class of things that the property can
be applied to. "
Is this correct?? Because if so, the semantics is wrong at this point. It says
<rdfs:domain,?P,?C> means: if <x,y> in IR(?P) then x in IC(?C)
but if the above is correct then it ought to say:
<rdfs:domain,?P,?C> means: if x in IC(?C) then for some y, <x,y> in IR(?P)
If the semantics is correct, however, then the example in the
walkthrough is rather misleading, and we will need to correct against
any potential misunderstanding. Also, in this case, HOW does someone
give a 'lower' bound to the domain of a property? Eg how can one say
that hasParent applies to *any* animal? (If both domain and range
restrict from above, then it would be consistent to give all
properties empty domains and ranges.)
I await clarification from the Semantic Gurus, and will write
appropriate prose for the walkthru when clarity is restored to my
mind.
Pat Hayes
PS. A related question. If
<rdfs:domain,?P,?D>
<rdfs:range,?P,?R>
<inverseOf,?P,?S>
does it follow that
<rdfs:domain, ?S,?R>
<rdfs:range,?S,?D>
??
PPS. The only way to really learn something is to try teaching it to
other people :-)
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