On 2021-03-24 8:48 am, Steve Ray wrote:
Also, the ambiguity in the example is that ex: represents both a
prefix found in the SPARQL query and also represents the URI for the
ontology in which the prefixes are defined. I had interpreted the
example at https://www.w3.org/TR/shacl/#sparql-constraints-example
<https://www.w3.org/TR/shacl/#sparql-constraints-example> to mean
"Identify all the prefixes you need in the query here" rather than "go
to this URI to find all the prefix definitions".
Also, by the way, I have never succeeded in using the prefix as in
your example at
https://www.w3.org/TR/shacl/#sparql-constraints-example
<https://www.w3.org/TR/shacl/#sparql-constraints-example>. In your
example you say
sh:prefixes ex: ;
sh:select """
I have only gotten it to work when I expand ex: to the full URI. I
wondered whether it was because the ex: turns into
http://example.com/ns# <http://example.com/ns#> and when I spell it
out I don't include the #, rather I write <http://example.com/ns
<http://example.com/ns>>.
Yes this is easy to get wrong. URLs ending with # are often used without
the # for the base URI/owl:Ontology. This problem doesn't exist for
namespaces ending with /
So regardless of the namespace, you typically want to reference the
*base URI* (aka named graph) which is where the owl:Ontology is. In the
SHACL spec's example that base URI and namespace are identical and both
end with the #. However, if you had
<http://example.com/ns>
a owl:Ontology ;
sh:declare ...
then you would use sh:prefixes <http://example.com/ns> without the hash.
For the examples and the SHACL namespace itself we chose to use a # URL
both for the namespace and the graph URI.
(These are very recurring questions not only from you, which indicates
that there is a deeper design problem with this aspect of the RDF world).
Holger
Steve
On Tue, Mar 23, 2021 at 3:32 PM Holger Knublauch
<[email protected] <mailto:[email protected]>> wrote:
On 2021-03-24 2:36 am, Steve Ray wrote:
I think the light bulb just went on.
Are you saying that the natural language interpretation of the
sh:prefixes triple *_inside_* a SPARQLRule is:
"Go to the following graph URI to get the definitions for the
prefixes you will need in the SPARQL query"...
...and in the ontology declaration, you use the sh:declare to do
those definitions. (without wrapping those sh:declare statements
inside a sh:prefixes clause)?
Yes exactly. The idea is that each graph declares its "main"
prefix and then includes the other prefixes that it needs via
owl:imports. Since the owl:imports are found at the graph URI
resource, this was a natural place to attach this info to, without
too much redundancy. Anyone who owl:imports your graph can then
use its own owl:Ontology and will get the other prefix
declarations automatically.
A problem is that this one example in the SHACL spec
https://www.w3.org/TR/shacl/#sparql-constraints-example
<https://www.w3.org/TR/shacl/#sparql-constraints-example>
doesn't include the triples behind ex: and most readers will not
scroll down to
https://www.w3.org/TR/shacl/#sparql-prefixes
<https://www.w3.org/TR/shacl/#sparql-prefixes>
for the full picture.
Holger
(I will test this while waiting for the Australian day to begin. :)
Steve
On Mon, Mar 22, 2021 at 4:49 PM Holger Knublauch
<[email protected] <mailto:[email protected]>> wrote:
In your first example, add
sh:rule [
a sh:SPARQLRule ;
sh:prefixes
<http://data.ashrae.org/standard223/1.0/inference/owl-subset>
<http://data.ashrae.org/standard223/1.0/inference/owl-subset> ;
because
<http://data.ashrae.org/standard223/1.0/inference/owl-subset>
<http://data.ashrae.org/standard223/1.0/inference/owl-subset>
sh:declare [
sh:namespace "http://www.w3.org/2002/07/owl#";
<http://www.w3.org/2002/07/owl#>^^xsd:anyURI ;
sh:prefix "owl" ;
] .
is already a correct prefix declaration.
If you attempt something like in your second example:
sh:prefixes <http://www.w3.org/2002/07/owl>
<http://www.w3.org/2002/07/owl> ;
then the assumption is that the following triples are present
<http://www.w3.org/2002/07/owl> <http://www.w3.org/2002/07/owl>
sh:declare [
sh:namespace "http://www.w3.org/2002/07/owl#";
<http://www.w3.org/2002/07/owl#>^^xsd:anyURI ;
sh:prefix "owl" ;
] .
which they are not.
There is clear evidence that too many people struggle with
this aspect of the SHACL spec, and that as an editor I should
have done a better job there. If I could simply re-upload the
SHACL spec this would be the first thing to fix. However, the
formal W3C process doesn't allow this easily.
I have to admit I never liked to even have the need to
declare those namespaces as triples - this is a mixed
blessing because nobody seems to understand the syntax yet
namespace prefixes are a serialization concept only, not a
graph concept. At some stage I may just give up on this and
change our SHACL engine to simply add the declared prefixes
from the files, like SPIN did for pragmatic reasons, ignoring
the spec.
BTW both examples have a mismatch between the baseURI and the
owl:Ontology. I suggest to keep them aligned.
HTH
Holger
On 2021-03-23 6:40 am, Steve Ray wrote:
I have been working around this problem by avoiding any
prefixes when defining a shape with SPARQL, but this still
bugs me. Attached are two tiny files, epp1.shapes.ttl and
epp2.shapes.ttl.
I'm running the SHACL reasoner.
epp1 works - it does not use any prefixes inside the shape.
epp2 is identical to epp1, except it declares the owl:
prefix in the shape.
TBC complains that it cannot resolve owl:SymmetricProperty.
I have tried following the documentation for this, but
clearly I'm getting something wrong. What am I missing?
Steve
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