Hi Steve,
your email appears unfinished so I wasn't sure when/whether to respond.
But the correct syntax for sh:filterShape would be like
sh:exists [
sh:filterShape qudt:Unit ;
sh:nodes [
sh:path [
sh:inversePath qudt:hasQuantityKind ;
] ;
] ;
]
i.e. it needs to be combined with sh:nodes. Imagine these node
expressions like a pipeline where the output of one step becomes the
input to the next. Here, the input nodes to the filterShape would be the
results of the sh:path expression.
HTH
Holger
On 10/30/2020 8:34 AM, Steve Ray wrote:
Thanks Holger! That worked! I had to rebalance some ]'s but then it
performed perfectly!
I'm still getting used to the syntax of the sh: operators. If I could
trouble you for one more piece of advice.
I realized that there are some instances of qudt:PhysicalConstant that
also point to instances of qudt:QuantityKind, so I want to filter out
anything that is not an instance of qudt:Unit. After exploring the
documentation at https://w3c.github.io/shacl/shacl-af
<https://w3c.github.io/shacl/shacl-af>, I thought sh:filterShape might
do the trick. The amended code is shown below. It isn't working - in
fact it is weirdly now returning just the value of $this, i.e. the
subject QuantityKind. Am I using sh:filterShape correctly? I'm trying
to say "Look to see if anything is pointing to you via the
hasQuantityKind property, and filter those down to just instances of
qudt:Unit. If you find some, return those. If not, follow the
skos:broader relation and try again with that QuantityKind."
Here is the functioning code:
qudt:QuantityKind-appropriateUnit
rdf:type sh:NodeShape ;
sh:property [
rdf:type sh:PropertyShape ;
sh:path qudt:appropriateUnit ;
sh:group qudt:AppropriateUnitsGroup ;
sh:order "15"^^xsd:decimal ;
sh:values [
sh:distinct [
sh:else [
sh:path qudt:appropriateUnit ;
sh:nodes [
sh:path skos:broader ;
] ;
] ;
sh:if [
sh:exists [
sh:path [
sh:inversePath qudt:hasQuantityKind ;
] ;
sh:filterShape qudt:Unit ;
] ;
] ;
sh:then [
sh:path [
sh:inversePath qudt:hasQuantityKind ;
] ;
sh:filterShape qudt:Unit ;
] ;
] ;
] ;
] ;
sh:targetClass qudt:QuantityKind ;
.
I realized that I need to
Steve
On Wed, Oct 28, 2020 at 7:39 PM Holger Knublauch
<hol...@topquadrant.com <mailto:hol...@topquadrant.com>> wrote:
On 10/29/2020 11:51 AM, Steve Ray wrote:
Hi,
I am trying to recreate a recursive magic property, using a SHACL
property shape. However, I suspect that the reason the recursion
is not working is because the property identified in the sh:path
statement isn't really a function in the same sense as a magic
property is a function.
My shape code is as follows:
qudt:QuantityKind-appropriateUnit
rdf:type sh:NodeShape ;
sh:property [
rdf:type sh:PropertyShape ;
sh:path qudt:dappropriateUnit ;
sh:values [
sh:prefixes <http://qudt.org/2.1/schema/shacl/overlay/qudt
<http://qudt.org/2.1/schema/shacl/overlay/qudt>> ;
sh:select """SELECT DISTINCT ?unit
WHERE {
{
?unit qudt:hasQuantityKind $this .
}
UNION
{
NOT EXISTS {
?unit qudt:hasQuantityKind $this .
} .
$this skos:broader ?parent1 .
?parent1 qudt:dappropriateUnit ?unit .
} .
}""" ;
] ;
] ;
sh:targetClass qudt:QuantityKind ;
.
The non-recursive part works (the first clause of the union). But
the second union clause does not work. Is there a way to make the
qudt:dappropriateUnit property know that there's this associated
sh:values clause?
As you have found out, SPARQL itself doesn't "see" the additional
inferred triples. SHACL node expressions do, if you can
reformulate this query, using sh:path.
In TopBraid there is a "native" way of querying inferred values
within SPARQL too:
Try
( ?parent1 qudt:dappropriateUnit ) tosh:values ?unit .
which is a magic property that will look at both inferred and
asserted values at query time. Make sure to avoid infinite loops
though, i.e. no cycles in the graph.
As this would only work within TopBraid, a more "standard"
approach would be to use node expressions. Something like
sh:values [
sh:distinct [
sh:if [
sh:exists [
sh:path [ sh:inversePath qudt:hasQuantityKind ]
]
] ;
sh:then [
sh:path [ sh:inversePath qudt:hasQuantityKind ]
]
] ;
sh:else [
sh:path qudt:dappropriateUnit ;
sh:nodes [
sh:path skos:broader ;
]
]
]
]
which due to the geekiness and my lack of example data I haven't
tested. It's another syntax for "If this has a subject for
hasQuantityKind then use that, otherwise recurse into the broader
parent". The sh:path near the sh:else would do the recursion
automatically, I believe.
https://w3c.github.io/shacl/shacl-af/#node-expressions-path
<https://w3c.github.io/shacl/shacl-af/#node-expressions-path>
(I just noticed the example there was wrong but this will
hopefully be fixed soon).
Holger
Steve
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