Feature: how to nest a joincondition inside a function?

[bjdmeest]

Came from kg-construct/rml-core#1

it is possible to nest functions (see eg https://github.com/RMLio/rml-fno-test-cases/blob/master/RMLFNOTC0018-CSV/mapping.ttl), so functions on top of functions, but not functions on top of joins.

[bjdmeest]

The whole 'functions on top of joins' is specifically about functions on top of (regular) join conditions.
However, for this to be actually useful, I believe we need kg-construct/mapping-challenges#29 tackled first (and how to specifically tackle this for values, is discussed in #4)

[bjdmeest]

An example would be, in YARRRML, based on https://rml.io/yarrrml/matey/ Advanced example:

prefixes:
  ex: "http://example.com/"

mappings:
  person:
    sources:
      - ['persons.json~jsonpath', '$.persons[*]']
    s: http://example.com/person/$(firstname)
    po:
      - [a, foaf:Person]
      - [ex:name, $(firstname)]
      - p: ex:likes
        o:
         - function: ex:getAfterHash
           parameters:
             - parameter: ex:param1
               value:
                 mapping: movie
                 condition:
                  function: equal
                  parameters:
                    - [str1, $(movie)]
                    - [str2, $(slug)]
  movie:
    sources:
      - ['movies.csv~csv']
    s: http://example.com/movie#$(slug)
    po:
      - [a, schema:Movie]

@dachafra did you have something like this in mind?

[andimou]

let's see how join conditions will evolve in RML before we go too far with this ;)

[bjdmeest]

I don't have a specific reference, but we at some point agreed that functions wouldn't work on top of joins, i.e. functions only work on one source at a time.
Meanwhile, RML-LV allows for joins. So when using standard FNML over a logicalView Source, we could have a function that uses data coming originally from another source. So I think this is in fact solved, but rather needs an example that combines FNML and LV