They are "just" instances of sh:ConstraintComponent that you can edit
with TBC. Look at the instances such as sh:ClassConstraintComponent in
dash.ttl for examples. In a nutshell, a constraint component defines the
names of parameters (sh:parameter) and one or more so-called validators.
The validators are typically SPARQL queries and in those the values of
the parameters can be used as pre-bound variables.
If you want to go down this route and run into roadblocks I'd be happy
to help you work out this use case.
Holger
On 12/07/2019 22:09, Fan Li wrote:
Hi Holger: Thanks for your detailed explanation! I am new to SHACL and
EDG... How can I define a new Constraint Component in EDG or Composer?
On Thursday, July 11, 2019 at 8:13:17 PM UTC-4, Holger Knublauch wrote:
On 12/07/2019 09:49, Rob Atkinson wrote:
Hi - I have been thinking about this too - it seems a challenge
in an "open world" or with large reference data sets.
sh:Class allows you to define an acceptable Class, which all your
country codes belong to - but to use this it means importing all
the content, (with explicit rdf:type declarations) into the graph
with the SHACL rules - this wont scale to a bigger dataset - such
as biological species, or even car models.
I wouldn't see that as a problem. The validation of sh:class
happens in the *data graph*, i.e. instances. The shapes graph only
need the class reference, e.g.
sh:class ex:Country
would suffice in the shapes graph, and only the data graph needs
to owl:import the actual instances of ex:Country.
Regardless of where these instances live, sh:class would be
insufficient to express that *only* those values are permitted for
any data graph. So for example, another data graph may owl:import
additional ex:Country instances, or even just define them itself.
The only built-in mechanism to cover finite enumerations in SHACL
core would be sh:in, but that will not scale for large data sets,
and is not very modular.
I believe this indicates the need for another SHACL constraint
component, which could have a syntax such as
ex:Address
sh:property [
sh:path ex:country ;
sh:class ex:Country ;
ext:graph <http://my-dataset.org> <http://my-dataset.org> ;
ext:classInGraph ex:Country ;
] .
This constraint component would take a graph and a class as
arguments, and then only permit the instances from the given
graph. Such a constraint component is reasonably easy to define in
SHACL-SPARQL, and is thus supported by the official standard, see
https://www.w3.org/TR/shacl/#constraint-components-syntax
<https://www.w3.org/TR/shacl/#constraint-components-syntax>
The SPARQL query would be something like
ASK {
GRAPH $graph {
$value rdf:type/rdfs:subClassOf* $classInGraph
}
}
(Replacing $graph with the given ext:graph and $classInGraph with
the given ext:classInGraph).
BTW in the example above I left the sh:class statement to help
tools such as input forms to still make sense of the situation -
these would not know much about the semantics of ext:classInGraph.
Maybe if the rules engine is expected to dereference a URI and
find the Class of the instance referenced - but that only works
in a Linked Data world where URIs will return an RDFS profile.
This may need a control on the rule - eg:sh_x:performLookup
rdfs:range xsd:Boolean
alternatively maybe a sh_xxx:lookup with options - e.g. a SPARQL
query template that names the graph - or maybe just the graph
identifier ?
Yes to the latter, see one such approach above.
Holger
On Friday, 12 July 2019 04:56:44 UTC+10, Fan Li wrote:
For example, if there is an attribute "country code", can I
constraint its value to one of them from the "Country Code"
reference dataset? Thanks!
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