Very different behavior on iterators compared to RMLViewer + RMLMapper

[termontwouter]

Following up on #3, but using LogicalViews, there's a big gap between what MappingWeaver allows to access array values, versus what RMLViewer + RMLMapper allow.

Given the following scaffolding:

:view a rml:LogicalView ;
  rml:viewOn [
    # JSONPath root iterator over { "key": [ "1", "2" ] }
  ] ;
  rml:field [
    rml:fieldName "key"
    # insert field definition from list below
  ] .

:mapping a rml:TriplesMap ;
  rml:logicalSource :view ;
  rml:subjectMap [ rml:termType rml:BlankNode ] ;
  rml:predicateObjectMap [
    rml:predicate <urn:example:hasValue> ;
    rml:objectMap [ 
      # insert corresponding reference from field definitions below
    ]
  ] .

A. With direct reference rml:reference "key" in the mapping:

• rml:reference "key[*]" in the view's field works
• rml:reference "$.key[*]" in the view's field works
• rml:reference "key" in the view's field fails in MappingWeaver
• rml:reference "$.key" in the view's field fails in MappingWeaver
• rml:iterator "$.key[*]" (without nested field) fails in MappingWeaver and RMLViewer+RMLMapper

B. With nested reference rml:reference "key.value" in the mapping:

1. Using rml:iterator "$.key[*]" ; rml:field [ rml:fieldName "value" ; ... ] in the view:

• rml:reference "@" in the nested field works (and MappingWeaver adds canonical type)
• rml:reference "[*]" in the nested field fails in MappingWeaver
• rml:reference "$" in the nested field fails in MappingWeaver

2. Using rml:iterator "key[*]" [ rml:fieldName "value" ; ... ] in the view, all of the references above (@, [*], $) fail in MappingWeaver

3. Using rml:iterator "$.key" [ rml:fieldName "value" ; ... ], in the view, all of the references above fail in MappingWeaver

4. Using rml:iterator "key" [ rml:fieldName "value" ; ... ], in the view, all of the references above fail in MappingWeaver

[termontwouter]

Given the long opening post, let me summarize the crucial differences that made my mappings not simply transportable from a working RMLViewer + RMLMapper setup to a MappingWeaver one:

• The latter requires the value of rml:iterator statements to start with the root ($); for rml:reference, this is not the case; in the former setup, both are allowed.

• The latter requires the value of rml:iterator statements to end with the index wildcard ([*]); in the former setup, this is not necessary.

• The latter fails on $ and [*] as rml:reference within an iterator field; in the former setup, this returns the iteration's value.

Note that I am not an RML expert, so I don't take a stance on which behavior correctly implements the RML spec.