Documenting missing feature in the specs: RML cannot handle JSON non objects array

[vemonet]

Issue type: ❓ Question

Is there any plan to solve this issue? #3 @thomas-delva

The issue was also mentioned here: RMLio/rmlmapper-java#95

In JSON there are 3 kind of objects:

• objects
• array
• array of objects.

Unfortunately RML cannot iterate on array, hence missing 1/3 of objects potentially expressed in a JSON file. Unfortunately this is preventing to use RML to map JSON to RDF, the loss of information (1/3) is too important

Would it be possible to make this issue clearly highlighted at the top of the RML specifications and documentations? So that new users are aware of the issue, and they know they should not consider using RML to map JSON files.

Note that in my experience, most mappings using RML required extensive preprocessing to overcome this crucial missing feature. Even for relatively simple JSON files (it's quite common to find non objects array in JSON)

Or maybe, would it be possible to add an exception for this use case? Maybe using something such as $($) or $(.), I am not specialist in JSONPath, but their might be a way to reference the root of an element, and RML should be able to pick it up.

Github already tracked it but I gave more detailed answer in the issue here

In summary: yes, we are certainly aiming to solve this issue