Support JSKOS as alternative output format

[nichtich]

Support JSKOS as alternative output format

[nichtich]

See https://github.com/gbv/mc2skos/tree/jskos for a first try based on rdflib-jsonld

• update JSKOS context document
• set @context field to URL instead of copying the full context in output
• find out how to iteratively convert RDF to JSKOS to process multiple records. Converting the full DDC would not work

[danmichaelo]

By "Converting the full DDC would not work", do you mean that it consumes too much memory? Serializing each concept in a streaming manner as it's processed instead of piling them all up in the graph would be good for all output formats, but not sure how to implement it without digging too much into rdflib internals. Perhaps it could work to serialize and flush the graph after each concept has been processed, but not sure what the overhead would be, and how to handle the context.

[nichtich]

Yes, I bet that streaming would be required at least for JSKOS - but I have not tested with a full DDC dump yet.

[danmichaelo]

When I'm converting a full DDC to Turtle, it uses about 400 MB of memory (or 500 when using all the flags), which isn't really an issue, even though streaming output would be much more elegant, and the lack of it is clearly one of the weak points of this tool.

[nichtich]

Ok - streaming is not actually needed. I'll further work on support of JSKOS.