"object" with complex type

Hello

I've a basic understanding of how to build a context in json-ld, but I
doesn't find how to compact a structure, which I get commonly by populating
an ontology
I've objects with structure like
    {
      "@id": "math:Competency134_0",
      "@type": [
        "math:hasCompetencyTarget",
        "owl:NamedIndividual"
      ],
      "math:hasBloomDescription": "math:Bloom_Taxonomy1",
      "math:hasTopic": "math:Topic152"
    },
    {
      "@id": "math:Competency22_0",
      "@type": [
        "math:hasCompetencyTarget",
        "owl:NamedIndividual"
      ],
      "math:hasBloomDescription": "math:Bloom_Taxonomy11",
      "math:hasTopic": "math:Topic15"
    },...
where math is just the prefix for my ontology

and expect to get something like
"competencies": [
"math:Competency134_0":
    {
      "math:hasBloomDescription": "math:Bloom_Taxonomy1",
      "math:hasTopic": "math:Topic152"
    },
"math:Competency22_0":
    {
      "math:hasBloomDescription": "math:Bloom_Taxonomy11",
      "math:hasTopic": "math:Topic15"
    },...
],

I've tried different context, but never approch something like this and
can't decide if I'm wrong to trying that and what simplication of my
json-ld I can really get with a context.
For example, I've tried several syntax for playing with an object having a
complex type and I never success; something like:
"competency": {
      "@id":  [
        "math:hasCompetencyTarget",
        "owl:NamedIndividual"
      ],
      "@type": "@id"
},
seems to be wrong
and is very similar to the 'Place' sample in the playground
    "image": {
      "@id": "http://schema.org/image",
      "@type": "@id"
    },


Thank's to give some help or just advice like 'read the section xxx of the
spec', 'look at the example here' or something like that
Than's in advance


--
Jean-Claude Moissinac

ᐧ