JSON-LD/RDF Round tripping? about json-ld-bp HOT 6 OPEN

The other thing complicating JSON-LD => RDF => JSON-LD round-tripping is array ordering. For example, an object with two values for rdf:type will have a random order when re-serialized to JSON-LD, as will any other cases where there are multiple values. This could possibly be addressed by a post-processing step when ordered all such values (being careful not to do this for lists), which would also require a valuator to provide to sort. While this might be important for test evaluation, it's of little value in the real world, and imposes a processing penalty that's probably not worth it.

Same thing for blank-node labels, and something like RDF Dataset Normalization, performed at the JSON-LD level, might be necessary to compare JSON-LD structures with each other.

One possible solution would be to largely abandon JSON to JSON comparisons and always compare the resulting RDF datasets. This would be a change from 1.0, and would not allow comparing non-RDF things such as @data values.

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Which is related to this issue where changing the ordering will change the compaction, as different scoped contexts would be chosen.

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Can we try to be precise? We have two different issues:

1. Round tripping to and from an RDF graph
2. Round tripping to and from a particular RDF syntax, most probably Turtle

On (1), I believe it is true that:

• Every RDF graph can be put into JSON-LD
• Some JSON-LD cannot be converted into (2), e.g., the blank node properties cited by @azaroth42.

The more problematic case is (2), also described in #13 (comment).

I think that, as far as the BP document goes, my take is that we should not use non-RDF features. We hardly had any use cases for literal-as-subject or bnode-as-predicates, and users should try to avoid that. I am not sure it is worth going way beyond that in the document.

As for (2), I am not sure what we can say.

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Can we separate out some tasks here?

Provide test cases for each non-round-tripping scenario

is clearly not in-scope for a best practices document. On the other hand, it seems very reasonable to me to offer some advice about problematic constructions here in the BP doc.

Do we actually have any use cases for literal-as-subject or bnode-as-predicates? I'm not asking because I think we do not: I genuinely do not remember hearing any, but I had plenty of chances to miss them! 😬

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Given the evolution of the "bnodes-as-predicates" discussion, I'm not entirely sure what we want to say here now. Do we want to say anything about JSON-LD 1.0 that uses bnodes and predicates and what that means for roundtripping?

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