Default serialization format for conjunctive graph is turtle, but turtle cannot handle quads (AFAIK)

[aucampia]

I believe turtle does not handle quads, but our default serialization format for ConjunctiveGraph is turtle as turtle does not override the default for Graph, I guess we should probably change this, question is to what.

I think TriG would make most sense, but the other option is n3.

[niklasl]

I agree that TriG is best. TriG is explicitly a superset of Turtle for supporting multiple named graphs (RDF datasets). Notation 3 is not a W3C REC, and it extends things with more complex structures (variables, graphs as formulas ("complex values") etc.). It is not (AFAIK) a superset of TriG (if it was, it could make sense).

[aucampia]

@WhiteGobo made a PR to fix this, but it occurs to me now that fixing this is potentially a breaking change.

There may be some mitigating factors, in that serializing a ConjunctiveGraph that contains quads outside the default graph using turtle generates output, but the output is wrong. And furthermore, serializing a ConjunctiveGraph that only had triples in the default graph as trig should result in valid turtle output.

Given these two conditions hold, I think it is okay to include a fix in version 6; otherwise this has to be merged in a way that only has an effect on version 7 onwards[ref].

CC: @RDFLib/core-reviewers

[aucampia]

This issue is somewhat related:

• Formats that don't support named graphs serialize Datasets and ConjunctiveGraphs with non-default graphs without raising any errors #2393

[aucampia]

Next release will be 7 and we will generally be more open to breaking changes going forward.