If the model says that Orange is equivalent class to the anonymous class
representing all things with the price of .25 and you have a lime that costs
.25, you will get a conclusion that this lime is an orange. And, if you have
a statement that these classes are distinct from each other, yes your model
will be inconsistent.
But this is a problem with the model, not a problem with the inferences. If
you don't want this to happen, you can say (as you have suggested) that
Orange is a subclass of the anonymous class representing all things with
the price of .25. You will not get a classification inference then.
< Also, the practice of attaching a property and a value restriction to a
class might make sense from an OO perspective, but it seems incorrect from a
modeling perspective. In fact, this is listed among the "Anti- patterns" in
Dean's book.>
I am not sure what you are talking about.
<How would a rule look that produces the fact that an individual orange(u)
hasPrice 25 cents?.>
# cls-hv1
CONSTRUCT {
?u ?p ?y .}
WHERE {
?x owl:hasValue ?y .
?x owl:onProperty ?p .
?u a ?x .
}
?x is a restriction (anonymous class), not :Orange
The inference that ?u a ?x if :Orange rdfs:subClassOf :?x and ?u a :Orange
comes from a different rule.
?u ?p ?v triple was indeed an unnecessary noise. Thanks for pointing it out.
Irene
From: [email protected]
[mailto:[email protected]] On Behalf Of Leonard Jacuzzo
Sent: Thursday, August 25, 2011 7:00 PM
To: [email protected]
Subject: Re: [topbraid-users] Re: Owlrl in SPARQL
Thanks Scott,
But it does not seem reasonable to assert that a lime is an orange simply
because it has the same price as an orange.
What would happen is the model contains 'Lime is distinct from Orange". This
would create an inconsistency...no?
Also, the practice of attaching a property and a value restriction to a
class might make sense from an OO perspective, but it seems incorrect from a
modeling perspective. In fact, this is listed among the "Anti- patterns" in
Dean's book.
As another question regarding rules.
Let's say that I avoid this OO pattern and instead define Orange as a
sublcass of a restriction on the property hasPrice to the value 25 cents.
(because that is better and true and would not result in anything having the
same price as an orange being classified as an orange)....
How would a rule look that produces the fact that an individual orange(u)
hasPrice 25 cents?.
So what I would have something like
Orange rdfs:subClassOf owl:restriction
owl:onProperty 'hasPrice'
owl: hasValue "..25" xsdfloat.
And
OrangeB rdf:type Orange.
How do I go from there to
OrangeB hasPrice value '.25' xsdfloat.
Sorry for the sloppy fake code..I am a neophyte.
Thanks again for your help. I have learned a great deal.
Best,
LFJ
So this rule is not truth preserving...in itself. It would only be truth
preserving with the appropriate "distinct' values.
On Thu, Aug 25, 2011 at 6:24 PM, Scott Henninger
<[email protected]> wrote:
Hello Leonard; Yes I do believe this is a typo in the rule set. We
will look into this some more and get it fixed for the 3.6 release.
The two rules, cls-hv1 and cls-hv2, are converses of each other. cls-
hv1 covers the case where if a class defines a hasValue restriction
property, then all members of the class must have that property
value. The rule infers this, in typical OWA fashion, making the model
consistent. So given a [:hasPrice value ".25"^^xsd:float] restriction
on :Orange, the triple {?u :hasPrice ".25"^^xsd:float} is inferred for
all members of Orange. Note that members of :Orange can also have
other :hasPrice values - e.g. {?u :hasPrice ".50"^^xsd:float} - and
that is consistent with the model.
The cls-hv2 covers the case that if a resource meets the hasValue
criteria, then it is a member of the class. So let's say we have an
instance with the triple {:alime a :Lime ; :hasPrice ".
25"^^xsd:float}, since the value of :hasPrice is .25, it meets the
criteria of :Orange membership and therefore the rule infers {:alime
a :Orange}. The tricky part to understand in this query is that ?u
refers to any resource. In our example the graph pattern is matched
as:
WHERE
{ ?x owl:hasValue ?y . ## ?x bound to bnode representing the
restriction, ?y bound to ".25"
?x owl:onProperty ?p . ## ?p bound to :hasPrice
?u ?p ?y . ## ?u bound to : alime
}
Try this in your SPARQL view by applying the above to a model that has
some hasValue restrictions. I'd suggest using 'SELECT *' so you can
follow the variable mappings.
<<BTW: what does it mean to assert that a class X hasValue y on
property P?
The class Orange does not have a price, only individual oranges have a
price.>>
If you are familiar with OO programming, this is akin to a class
variable. hasValue restrictions are defined on the class and applies
"automatically" to all instances. This is basically what cls-hv1
does. cls-hv2 allows you to also infer that anything with the
property-value pair is a member of the class.
-- Scott
On Aug 25, 3:39 pm, Leonard Jacuzzo <[email protected]> wrote:
> Hello list,
>
> Thank you for all of the help that you have been to me in understanding
how
> to use SPARQL for rule creation.
>
> I have a few questions.
>
> I was looking over the specification of OWL-RL
athttp://topbraid.org/spin/owlrl-all.html
>
> The rule cls hv1 has a typo in it. The last triple in the WHERE clause has
> not function in the rule and is not part of the W3C specification. That is
> "?u?p ?v should be removed. Here is the rule as it stands.
> # cls-hv1
> CONSTRUCT {
> ?u ?p ?y .}
>
> WHERE {
> ?x owl:hasValue ?y .
> ?x owl:onProperty ?p .
> ?u a ?x .
> ?u ?p ?v .
>
> }
>
> I am also confused by the following rule, which conforms to the W3C, but
> makes no sense to me. Can you explain it to me?
> Here is the rule:
> # cls-hv2
> CONSTRUCT {
> ?u a ?x .}
>
> WHERE {
> ?x owl:hasValue ?y .
> ?x owl:onProperty ?p .
> ?u ?p ?y .
>
> }
>
> The reason that I am confused is that it seems easy to come up with a
> counter example. E.G. imagine that the class "Orange' hasvalue .25 on the
> property "hasPrice" (so oranges are priced at 25 cents) Further imagine
that
> some individual lime(u) hasPrice .25. It does not follow from this that
Lime
> (u) is a lemon.
>
> What am I missing in my understanding of this rule?
>
> BTW: what does it mean to assert that a class X hasValue y on property P?
> The class Orange does not have a price, only individual oranges have a
> price. Should this be a Orange is a subclass of the restriction on the
> property "hasPrice" to the value 25 cents? When would a person use the
> structure in the WHERE clause?
>
> I have one more question about rules, but I will wait until I think some
> more.
>
> Thank you for reading this. Any help will be great,
> LFJ
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