Base IRI for RMLMapper

[marioscrock]

Hi everyone,
the YARRRML specification allows to specify a base IRI saying

This IRI will be used for the creation of the IRIs of the term maps and sources of the [R2]RML rules.

As far as I understand, the specified IRI is set as prefix ":" and added to the term maps. However, the RMLMapper parses the @base keyword in Turtle to extract the base IRI and therefore, no baseIRI is found if the file produced by the parser is directly used. Moreover, I would suggest to extend the YARRRML specification and to allow defining two different "base" prefixes, one for mappings (maybe a prefix + IRI can be specified and used for mappings) and the other one to be used as base IRI for triples generated in the mapping procedure (set as @base IRI in the resulting RML file and therefore considered by the RMLMapper as base IRI to complete relative IRIs). Please correct me if I got it wrong or let me know if there is already a way to specify prefixes as described. Thank you in advance.

[pheyvaer]

Hi @marioscrock

Yes, this indeed sounds as a valid remark to me. Could you maybe add an example of what you are describing here to make sure we are on the same page? And of your proposed solution? Thanks!

[marioscrock]

Hi @pheyvaer yes sure!

Let's assume it exists a student-ontology (std: https://w3id.org/student-ontology#) and a mapping file associated:

prefixes:
  std: "https://w3id.org/student-ontology#"

base: "http://www.student-ontology.com/mappings/"

mappings:
  students:
    sources:
      - ["students.txt~csv"]
    s: Student-$(name)
    po:
      - [a, std:Student]
      - [std:name, "$(name)"]
      - [std:surname, $(surname)]

The base IRI specified is used for term maps and the result of the yarrrml parsing procedure is:

@prefix rr: <http://www.w3.org/ns/r2rml#>.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix fnml: <http://semweb.mmlab.be/ns/fnml#>.
@prefix fno: <http://w3id.org/function/ontology#>.
@prefix rml: <http://semweb.mmlab.be/ns/rml#>.
@prefix ql: <http://semweb.mmlab.be/ns/ql#>.
@prefix : <http://www.student-ontology.com/mappings/>.
@prefix std: <https://w3id.org/student-ontology#>.

:map_students_0 rml:logicalSource :source_0.
:source_0 a rml:LogicalSource;
    rml:source "students.txt";
    rml:referenceFormulation ql:CSV.
:map_students_0 a rr:TriplesMap;
    rdfs:label "students".
:s_0 a rr:SubjectMap.
:map_students_0 rr:subjectMap :s_0.
:s_0 rr:template "Student-{name}".
:pom_0 a rr:PredicateObjectMap.
:map_students_0 rr:predicateObjectMap :pom_0.
:pm_0 a rr:PredicateMap.
:pom_0 rr:predicateMap :pm_0.
:pm_0 rr:constant rdf:type.
:pom_0 rr:objectMap :om_0.
:om_0 a rr:ObjectMap;
    rr:constant "https://w3id.org/student-ontology#Student";
    rr:termType rr:IRI.
:pom_1 a rr:PredicateObjectMap.
:map_students_0 rr:predicateObjectMap :pom_1.
:pm_1 a rr:PredicateMap.
:pom_1 rr:predicateMap :pm_1.
:pm_1 rr:constant std:name.
:pom_1 rr:objectMap :om_1.
:om_1 a rr:ObjectMap;
    rml:reference "name";
    rr:termType rr:Literal.
:pom_2 a rr:PredicateObjectMap.
:map_students_0 rr:predicateObjectMap :pom_2.
:pm_2 a rr:PredicateMap.
:pom_2 rr:predicateMap :pm_2.
:pm_2 rr:constant std:surname.
:pom_2 rr:objectMap :om_2.
:om_2 a rr:ObjectMap;
    rml:reference "surname";
    rr:termType rr:Literal.

If this file is used with the RMLMapper, it throws the following error The base IRI is null, so relative IRI of subject cannot be turned in to absolute IRI since it tries to parse the @base keyword not present in the RML mapping file. However, if @base <http://www.my-university.org/students/> . is added to the generated RML file it works as expected. Example:

name,surname
Paolo,Rossi

generates:

<http://www.my-university.org/students/Student-Paolo> a std:Student;
  std:name "Paolo";
  std:surname "Rossi" .

What I would like to have is the possibility of specifying one IRI for mapping term maps, e.g. an IRI associated somehow also to the ontology (as in the example), and one IRI to be used from the RMLMapper for the triples generated, e.g. related to the specific university compiling the yarrrml and executing the mappings. My proposal is to have two directives in the yarrrml file, one allowing to specify a prefix+IRI used for generating mapping term maps, and the other to specify the IRI then added as @base and therefore used by the RMLMapper.

Example:

prefixes:
  std: "https://w3id.org/student-ontology#"
terms: 
  stdm: "http://www.student-ontology.com/mappings/"

base: "http://www.my-university.org/students/"

mappings:
  students:
    sources:
      - ["students.txt~csv"]
    s: Student-$(name)
    po:
      - [a, std:Student]
      - [std:name, "$(name)"]
      - [std:surname, $(surname)]

Producing as result:

@base <http://www.my-university.org/students/> .
@prefix rr: <http://www.w3.org/ns/r2rml#>.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix fnml: <http://semweb.mmlab.be/ns/fnml#>.
@prefix fno: <http://w3id.org/function/ontology#>.
@prefix rml: <http://semweb.mmlab.be/ns/rml#>.
@prefix ql: <http://semweb.mmlab.be/ns/ql#>.
@prefix stdm: <http://www.student-ontology.com/mappings/>.
@prefix std: <https://w3id.org/student-ontology#>.

stdm:map_students_0 rml:logicalSource stdm:source_0.
stdm:source_0 a rml:LogicalSource;
    rml:source "students.txt";
    rml:referenceFormulation ql:CSV.
stdm:map_students_0 a rr:TriplesMap;
    rdfs:label "students".
stdm:s_0 a rr:SubjectMap.
stdm:map_students_0 rr:subjectMap stdm:s_0.
stdm:s_0 rr:template "Student-{name}".
stdm:pom_0 a rr:PredicateObjectMap.
stdm:map_students_0 rr:predicateObjectMap stdm:pom_0.
stdm:pm_0 a rr:PredicateMap.
stdm:pom_0 rr:predicateMap stdm:pm_0.
stdm:pm_0 rr:constant rdf:type.
stdm:pom_0 rr:objectMap stdm:om_0.
stdm:om_0 a rr:ObjectMap;
    rr:constant "https://w3id.org/student-ontology#Student";
    rr:termType rr:IRI.
stdm:pom_1 a rr:PredicateObjectMap.
stdm:map_students_0 rr:predicateObjectMap stdm:pom_1.
stdm:pm_1 a rr:PredicateMap.
stdm:pom_1 rr:predicateMap stdm:pm_1.
stdm:pm_1 rr:constant std:name.
stdm:pom_1 rr:objectMap stdm:om_1.
stdm:om_1 a rr:ObjectMap;
    rml:reference "name";
    rr:termType rr:Literal.
stdm:pom_2 a rr:PredicateObjectMap.
stdm:map_students_0 rr:predicateObjectMap stdm:pom_2.
stdm:pm_2 a rr:PredicateMap.
stdm:pom_2 rr:predicateMap stdm:pm_2.
stdm:pm_2 rr:constant std:surname.
stdm:pom_2 rr:objectMap stdm:om_2.
stdm:om_2 a rr:ObjectMap;
    rml:reference "surname";
    rr:termType rr:Literal.