Re: [spr35236] Problem with namespace resolution for AG in CL

Hi Stewart,


> but when I run a simple query like (sparql:run-sparql " SELECT DISTINCT ?s ?o
> WHERE { ?s rdfs:subClassOf ?o}"), I get this error (and the same for any other
> Qnames I try to use):


AllegroGraph's namespace mechanism is used for resolving future-parts with the '!' syntax: e.g.,


   (add-triple !rdf:type !rdfs:label !"type")


It doesn't apply to SPARQL, because the SPARQL standard specifies its own namespace prefix mechanism.


The correct way to do things in SPARQL is

(sparql:run-sparql "
   PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
   SELECT DISTINCT ?s ?o
   WHERE {
     ?s rdfs:subClassOf ?o
   }")


As a shorthand, you can supply a hash-table of the correct 'shape' as the value of the :default-prefixes argument, which 
*namespaces* just so happens to be:


(sparql:run-sparql "
   SELECT DISTINCT ?s ?o
   WHERE {
     ?s rdfs:subClassOf ?o
   }"
   :default-prefixes db.agraph::*namespaces*)


This is mentioned in the documentation for run-sparql if you would like more details.


While convenient, this approach is generally inadvisable for 'real' code that you intend to keep and continue to use, 
because the binding of *namespaces* can change.

If it does, the meaning of your query will change: for example, rdfs: could expand to a different URI, or it could be 
removed entirely (resulting in a query parse error at runtime).


Let me know if that answers your question.

Regards,

-Richard