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JARQL: SPARQL for JSON

Jarql is a tool, inspired by Tarql, for converting JSON to RDF using SPARQL 1.1 syntax, using construct queries.

Introduction

JARQL reads a JSON file from input and converts it in a raw graph using the Jarql namespace (jarql: <http://jarql.com/>). The idea is to convert the JSON in a graph on which you can apply SPARQL CONSTRUCT queries to create the RDF graph that you want.

How it works

The root of the JSON file is identified by jarql:root and each key becomes a property of the same namespace. For example the key name becomes jarql:name. So a minimal example like:

{ "fieldName": "fieldValue" }

produces:

jarql:root jarql:filedName "fieldValue"

A nested object becomes a blank node. So if you have:

{
    "name": "Paolino",
    "surname": "Paperino",
    "uncle": {
        "name": "Paperone",
        "surname": "De Paperoni"
    }
}

you can access to "name": "Paperone" using a variable ?uncle that identifies the blank node:

...
WHERE {
    jarql:root jarql:uncle ?uncle .
    ?uncle jarql:name ?uncleName .
}
...

Instead, if you have an array:

{
    "name": "Paperino",
    "nephew": ["Qui", "Quo", "Qua"]
}

every element inside it becomes one object with the JSON-key of the array as property pointing to it:

@prefix jarql: <http://jarql.com/>.
jarql:root jarql:name "Paperino";
           jarql:nephew "Qui", "Quo", "Qua"

that can be queried by:

...
WHERE {
    jarql:root jarql:nephew ?nephew .
}
...

Usage

java -jar jarql-<version>.jar <JSON-File> <Query-File>

So if your JSON is called foobar.json and you setup a query file called foobar.query and the latest software version is 1.0-pre1 you can run:

java -jar jarql-1.0-pre1.jar foobar.json foobar.query

Examples

Example 1 (Tenders in Paperopoli)

JSON input file

{
    "cig": "XXXX4A36A7",
    "strutturaProponente": {
        "codiceFiscaleProp": "01111111111",
        "denominazione": "Comune di Paperopoli"
    },
    "oggetto": "Costruzione di un grande deposito su una collina.",
    "partecipanti": [
        {
            "ragioneSociale": "OCOPOLI COSTRUZIONI S.R.L.",
            "vatID": "42424242424"
        },
        {
            "ragioneSociale": "DE PAPERONI S.P.A.",
            "vatID": "23232323232"
        }
    ]
}

RAW graph automagically created

@prefix jarql: <http://jarql.com/>.
jarql:root jarql:cig "XXXX4A36A7";
           jarql:strutturaProponente [
               jarql:codiceFiscaleProp "01111111111";
               jarql:denominazione "Comune di Paperopoli"
           ];
           jarql:oggetto "Costruzione di un grande deposito su una collina.";
           jarql:partecipanti [
               jarql:ragioneSociale "OCOPOLI COSTRUZIONI S.R.L.";
               jarql:vatID "42424242424"
           ];
           jarql:partecipanti [
               jarql:ragioneSociale "DE PAPERONI S.P.A.";
               jarql:vatID "23232323232"
].

SPARQL input query

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX dcterm: <http://purl.org/dc/terms/>
PREFIX pc: <http://contrattipubblici.org/>
PREFIX jarql: <http://jarql.com/> 

CONSTRUCT { 
  ?URI a "Contract";
       dcterm:identifier ?cig;
       pc:contractingAuth ?URIpa;
       rdfs:label ?oggetto.
  ?URIpa a "PubAdmin";
       rdfs:label ?denominazione;
       dcterm:identifier ?codiceFiscaleProp.
  ?URIpart a "Participant";
       rdfs:label ?ragioneSocialePart;
       dcterm:identifier ?vatIDPart.
}
WHERE {
  jarql:root jarql:cig ?cig.
  BIND(URI(CONCAT("http://test.yo/", MD5(?cig))) as ?URI).
  jarql:root jarql:strutturaProponente ?proponente.
  ?proponente jarql:codiceFiscaleProp ?codiceFiscaleProp.
  ?proponente jarql:denominazione ?denominazione.
  BIND(URI(CONCAT("http://test.yo/", MD5(?codiceFiscaleProp))) as ?URIpa).
  jarql:root jarql:oggetto ?oggetto.
  jarql:root jarql:partecipanti ?partecipanti.
  ?partecipanti jarql:ragioneSociale ?ragioneSocialePart.
  ?partecipanti jarql:vatID ?vatIDPart.
  BIND(URI(CONCAT("http://test.yo/", MD5(?vatIDPart))) as ?URIpart).
}

RDF in output

<http://test.yo/1f839a6f81727fc54c06d4e4be5bc51e>
        a       "Participant"^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://www.w3.org/2000/01/rdf-schema#label>
                "DE PAPERONI S.P.A."^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://purl.org/dc/terms/identifier>
                "23232323232"^^<http://www.w3.org/2001/XMLSchema#string> .

<http://test.yo/0e2d5004f3fdb311f2832aa0e08031a2>
        a       "PubAdmin"^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://www.w3.org/2000/01/rdf-schema#label>
                "Comune di Paperopoli"^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://purl.org/dc/terms/identifier>
                "01111111111"^^<http://www.w3.org/2001/XMLSchema#string> .

<http://test.yo/a80ebd2e303fa3ca5eb53f2dfb689186>
        a       "Participant"^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://www.w3.org/2000/01/rdf-schema#label>
                "OCOPOLI COSTRUZIONI S.R.L."^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://purl.org/dc/terms/identifier>
                "42424242424"^^<http://www.w3.org/2001/XMLSchema#string> .

<http://test.yo/cc44b6b5f7889c004a399e90679996a0>
        a       "Contract"^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://www.w3.org/2000/01/rdf-schema#label>
                "Costruzione di un grande deposito su una collina."^^<http://www.w3.org/2001/XMLSchema#string> ;
        <http://contrattipubblici.org/contractingAuth>
                <http://test.yo/0e2d5004f3fdb311f2832aa0e08031a2> ;
        <http://purl.org/dc/terms/identifier>
"XXXX4A36A7"^^<http://www.w3.org/2001/XMLSchema#string> .

Limitations

  • Nested arrays in JSON are not supported.
  • The order of JSON elements in an array is irrelevant (so you can't use their order as a way to construct the RDF with enumerative properties).