why the output not included prefixes

[Amrosx]

this is the body

{ "rml": "@prefix rr: <http://www.w3.org/ns/r2rml#>. @prefix rml: <http://semweb.mmlab.be/ns/rml#>. @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>. @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>. @prefix ql: <http://semweb.mmlab.be/ns/ql#>. @prefix map: <http://mapping.example.com/>. map:map_person_0 rml:logicalSource map:source_0; a rr:TriplesMap; rdfs:label \"person\"; rr:subjectMap map:s_0; rr:predicateObjectMap map:pom_0, map:pom_1. map:om_0 a rr:ObjectMap; rr:constant \"http://xmlns.com/foaf/0.1/Person\"; rr:termType rr:IRI. map:om_1 a rr:ObjectMap; rml:reference \"firstname\"; rr:termType rr:Literal. map:pm_0 a rr:PredicateMap; rr:constant rdf:type. map:pm_1 a rr:PredicateMap; rr:constant <http://example.com/name>. map:pom_0 a rr:PredicateObjectMap; rr:predicateMap map:pm_0; rr:objectMap map:om_0. map:pom_1 a rr:PredicateObjectMap; rr:predicateMap map:pm_1; rr:objectMap map:om_1. map:s_0 a rr:SubjectMap; rr:template \"http://example.com/{firstname}\". map:source_0 a rml:LogicalSource; rml:source \"data.json\"; rml:iterator \"$.persons[*]\"; rml:referenceFormulation ql:JSONPath.", "sources": { "data.json": "{ \"persons\": [ { \"firstname\": \"John\", \"lastname\": \"Doe\" }, { \"firstname\": \"Jane\", \"lastname\": \"Smith\" }, { \"firstname\": \"Sarah\", \"lastname\": \"Bladinck\" } ] }" }, "serialization": "turtle" }

this is the result wihout the prefixes ?? and if you mapp direct from jar file it print out the prefixes.

{ "output": "\n<http://example.com/Jane> a <http://xmlns.com/foaf/0.1/Person>;\n <http://example.com/name> \"Jane\" .\n\n<http://example.com/John> a <http://xmlns.com/foaf/0.1/Person>;\n <http://example.com/name> \"John\" .\n\n<http://example.com/Sarah> a <http://xmlns.com/foaf/0.1/Person>;\n <http://example.com/name> \"Sarah\" .\n" }

[pheyvaer]

The reason is that the Web API returns the results as N-Quads, while the default for the RMLMapper is Turtle. A new feature has been added to the RMLMapper (and consequently also the Web API) that allows you to set the Target of a mapping. This target allows you also to define what serialization format is used for the output.