revert colons in qnames?

[joernhees]

The change of #663 caused the following changed behavior:

import rdflib
print(rdflib.Graph().namespace_manager.compute_qname('http://dbpedia.org/page/Category:Software_bugs'))

before:

('ns1', rdflib.term.URIRef('http://dbpedia.org/page/Category:'), 'Software_bugs')

after:

('ns1', rdflib.term.URIRef('http://dbpedia.org/page/'), 'Category:Software_bugs')

The generated normalized URI causes trouble on for example the DBpedia endpoint:

prefix ns1: <http://dbpedia.org/page/>
select * { ?s ?p ns1:Category:Software_bugs }

On closer inspection ns1:Category:Software_bugs is however both: a valid CURIE and a valid SPARQL PrefixedName, so this is likely a Virtuoso bug.

ns1:Category:Software_bugs is however not a valid QName, which given the name of the compute_qname function is at least problematic.

Maybe as #649 is already dealing with this by introducing a compute_qname_strict, it could be solved in there, maybe by just renaming the new compute_qname to compute_curie and give it a dialect arg???

[tgbugs]

The compute_curie option seems reasonable. I tried a number of variants when implementing compute_qname_strict and it seemed that it was more performant to not have to check whether it was strict or not every time. The same might be true of a dialect arg. There are a number of other use cases for dialect args, e.g. whether a / should be allowed in the suffix.

When I was working on this I recall finding many bugs in other rdf parsing/serializing libs because they had not dealt with the fact that curies are not strictly qnames, so the virtuoso issue wouldn't surprise me at all.