How to nest rdf triples for json-ld output?

[foster...@gmail.com]

Hello, I'm a newbie to rdflib and also to LOD in general.

I'm trying to generate the following using the rdflib-jsonld plugin.

"rdfs:label": {
"en": "mentors",
},
"owl:inverseOf": {
"rdfs:label": {
"en": "is mentored by",
}

I haven't figured out how to get the nested structure of inverseOf - label. Here's a snippet of my attempt, which didn't seem right and isn't.

ref = URIRef(some_namespace["mentor"])
store.add((ref, RDFS.label, Literal("mentors", lang="en")))
store.add((ref, RDFS.label, Literal("is mentored by", lang="en")))
store.add((ref, OWL.inverse, Literal("is mentored by")))

This gives:

"owl:inverse": "is mentored by",
"rdfs:label": [
{
"@language": "en",
"@value": "is mentored by"
},
{
"@language": "en",
"@value": "mentors"
}
]

Thanks in advance for your help!
Lynn

[Niklas Lindström]

Hello Lynn,

I believe this code should create the graph you need, and serialize it:

- - - 8< - - -

from rdflib import *

some_namespace = Namespace("http://example.org/ns/")

graph = Graph()

ref = URIRef(some_namespace["mentor"])

graph.add((ref, RDFS.label, Literal("mentors", lang="en")))

inverse = BNode()

graph.add((ref, OWL.inverseOf, inverse))

graph.add((inverse, RDFS.label, Literal("is mentored by", lang="en")))

output = graph.serialize(format='json-ld', context={

        'rdfs': unicode(RDFS),

        'owl': unicode(OWL),

        'rdfs:label': {'@container': '@language'}

    })

print(output)

- - - >8 - - -

Notice that I supply an explicit context, where rdfs:label is defined as using the @container: @language construct. This tells the compaction algorithm to build dictionaries for labels using their @language as keys.

The compacted output will be like:

- - - 8< - - -

{

  "@context": {

    "owl": "http://www.w3.org/2002/07/owl#",

    "rdfs": "http://www.w3.org/2000/01/rdf-schema#",

    "rdfs:label": {"@container": "@language"}

  },

  "@graph": [

    {

      "@id": "http://example.org/ns/mentor",

      "owl:inverseOf": {"@id": "_:b1"},

      "rdfs:label": {"en": "mentors"}

    },

    {

      "@id": "_:b1",

      "rdfs:label": {"en": "is mentored by"}

    }

  ]

}

- - - >8 - - -

The remaining thing to do to reach your desired form is to frame this by some means, to inline the bnode (_:b1) where it is referenced.

For basic forms you can do this manually by manipulating the resulting JSON. For this case, the following should do the trick:

- - - 8< - - -

def simplyframe(data):

    items, refs = {}, {}

    for item in data['@graph']:

        itemid = item.get('@id')

        if itemid:

            items[itemid] = item

        for vs in item.values():

            for v in [vs] if not isinstance(vs, list) else vs:

                if isinstance(v, dict):

                    refid = v.get('@id')

                    if refid and refid.startswith('_:'):

                        refs.setdefault(refid, (v, []))[1].append(item)

    for ref, subjects in refs.values():

        if len(subjects) == 1:

            ref.update(items.pop(ref['@id']))

            del ref['@id']

    data['@graph'] = items.values()

import json

data = json.loads(output)

simplyframe(data)

print json.dumps(data, indent=2)

- - - >8 - - -

Phew. :) While rdflib-jsonld does not yet do this, I might add a simple option to achieve the above (i.e. to just embed bnodes which are only referenced once). I also have a mechanism for automatic framing which achieves this (and much more) in the works. (I use it in current work, and you can see a version of it here [1].)

I hope this helps in some respect.

Cheers,

Niklas

[1]: https://github.com/libris/lddb/blob/489c66b3fef8/lddb/ld/frame.py

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[Lynn Foster]

Niklas, Thanks so much for your very thorough help!! 

Lynn

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