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> ;
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
(I just noticed the example there was wrong but this will hopefully be
fixed soon).
Holger
Steve
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