How do I compact and/or frame a json-ld document so that IRI values are expressed succinctly as well as keys? - json-ld

Question

Given an original JSON-LD document like this example, which defines the sources for some thing1:
[
{
"#id": "https://example.com/thing1",
"https://example.com/sources": [
{
"#id": "https://example.com/vocab/countries/EN"
},
{
"#id": "https://example.com/vocab/countries/FR"
}
]
}
]
(I'm simplifying quite a lot - in my real use-case this is larger and generated from RDF data. ex:vocab/countries is a SKOS ConceptScheme including EN and FR as Concepts)
I want to collapse it into something approximating what I'd use to express that in more normal JSON:
{
"#id": "https://example.com/thing1",
"sources": ["EN", "FR"]
}
I find I can use a context to collapse into name/values and shorten the names:
{
"#context": {
"#version": 1.1,
"ex": "https://example.com/",
"sources": {
"#id": "ex:sources",
"#type": "#id"
}
},
"#id": "ex:thing1",
"sources": [
"ex:vocab/countries/EN",
"ex:vocab/countries/FR"
]
}
An important element is "#type": "#id" which collapses the source definitions from (a list of) objects into key/value pairs, and the enclosing context term maps https://example.com/sources to sources.
But I cannot find a way which seems to do the same on the values, so that they become EN and FR instead of ex:vocab/countries/EN and ex:vocab/countries/FR. My experiments with adding #base and #vocab properties to the context don't appear to work like I expected them to.
I also need to do this in a scoped way, so that other properties besides sources can be defined which reference different vocabularies. For instance I might want to include languages, which could include terms from a vocabulary representing English, French, Gaelic, Breton, etc. In other words, I can't just set a global vocabulary or base for the entire document.
Can anyone tell me if this kind of transform is possible, and if so, how to achieve it?
JSON-LD Playground link here

Answer 1

You could set the expected values of sources to #vocab instead of #type and use a scoped context to set the #vocab to use. For example:
{
"#version": 1.1,
"ex": "https://example.com/",
"sources": {
"#id": "ex:sources",
"#type": "#vocab",
"#context": {
"#vocab": "https://example.com/vocab/countries/"
}
}
}
(playground link).
This says to treat the values of playground as vocabulary-relative IRIs, and sets the base of that vocabulary for those values. You should get the following:
{
"#context": {
"#version": 1.1,
"ex": "https://example.com/",
"sources": {
"#id": "ex:sources",
"#type": "#vocab",
"#context": {
"#vocab": "https://example.com/vocab/countries/"
}
}
},
"#id": "ex:thing1",
"sources": [
"EN",
"FR"
]
}