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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