`rdf_update/4` introduces duplicate quads

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`rdf_update/4` introduces duplicate quads #28

Closed wouterbeek closed 7 years ago

wouterbeek commented 8 years ago

rdf_update/4 is able to introduce duplicate quadruples, something that cannot be achieved with rdf_assert/4. This seems to be unintended?

?- [library(semweb/rdf_db)].
?- rdf_assert(a, b, c, x).
?- rdf_assert(a, b, c, y).
?- rdf_update(a, b, c, graph(z)).
?- rdf(S, P, O, G), writeln(rdf(S,P,O,G)), fail.
rdf(a,b,c,z).
rdf(a,b,c,z).
false.

wouterbeek commented 7 years ago

This is now fixed in rdf11 by disallowing Action = graph(+) for the ternary predicate.