sparqljson-parse

Parses SPARQL JSON query results

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SPARQL-Results+JSON Parse
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A utility package that allows you to parse SPARQL JSON results in a convenient RDF/JS-based datastructure.
For example, the following SPARQL JSON result can be converted as follows:
In:
{
  "head": {
    "vars": [
      "book"
      ]
  },
  "results": {
    "bindings": [
      { "book": { "type": "uri", "value": "http://example.org/book/book1" } },
      { "book": { "type": "uri", "value": "http://example.org/book/book2" } },
      { "book": { "type": "uri", "value": "http://example.org/book/book3" } },
      { "book": { "type": "uri", "value": "http://example.org/book/book4" } },
      { "book": { "type": "uri", "value": "http://example.org/book/book5" } },
      {
        "book": {
          "type": "triple",
          "value": {
            "subject": {
              "type": "uri",
              "value": "http://example.org/alice"
            },
            "predicate": {
              "type": "uri",
              "value": "http://example.org/name"
            }
          }
        }
      }
    ]
  }
}

Out:
[
  { '?book': namedNode('http://example.org/book/book1') },
  { '?book': namedNode('http://example.org/book/book2') },
  { '?book': namedNode('http://example.org/book/book3') },
  { '?book': namedNode('http://example.org/book/book4') },
  { '?book': namedNode('http://example.org/book/book5') },
    { '?book': quad(namedNode('http://example.org/bob'), namedNode('http://example.org/name'), literal('Bob', namedNode('http://example.org/Type'))) },
]

Where namedNode is an RDF/JS named node, quad is an RDF/JS quad/triple, and literal is an RDF/JS literal.
This library automatically converts all SPARQL JSON result values to their respective RDF/JS type.

Usage

Create a new parser

import {SparqlJsonParser} from "sparqljson-parse";

const sparqlJsonParser = new SparqlJsonParser();

Optionally, you can provide a settings object to the constructor with optional parameters:
const sparqlJsonParser = new SparqlJsonParser({
  dataFactory: dataFactory, // A custom RDFJS datafactory
  prefixVariableQuestionMark: true, // If variable names in the output should be prefixed with '?', default is false.
});

Convert single bindings

sparqlJsonParser.parseJsonBindings({ "book": { "type": "uri", "value": "http://example.org/book/book1" } })
// This will output { '?book': namedNode('http://example.org/book/book1') }

Convert a full SPARQL JSON response

const sparqlJsonresponse = {
                             "head": {
                               "vars": [
                                 "book"
                                 ]
                             },
                             "results": {
                               "bindings": [
                                 { "book": { "type": "uri", "value": "http://example.org/book/book1" } }
                               ]
                             }
                           };
sparqlJsonParser.parseJsonResults(sparqlJsonresponse);
// This will output [ { '?book': namedNode('http://example.org/book/book1') } ]

Convert a full SPARQL JSON boolean response

const sparqlJsonresponse = {
                             "head": {},
                             "boolean": true
                           };
sparqlJsonParser.parseJsonBoolean(sparqlJsonresponse);
// This will output true

Convert a SPARQL JSON stream

If you have many query results, then a streaming-based approach might be more efficient. In this case, you can use the sparqlJsonParser.parseJsonResultsStream method, which takes a Node readable stream of SPARQL JSON results as a text stream, and outputs a stream of parsed bindings.
Optionally, you can also retrieve the variables inside the head as follows by listening to the variables event:
sparqlJsonParser.parseJsonResultsStream(myStream)
    .on('variables', (variables: RDF.Variable[]) => console.log(variables))
    .on('data', (bindings: IBindings) => console.log(bindings));

sparqlJsonParser.parseJsonBooleanStream also takes a stream as input, but it returns a promise that resolves to a boolean.

Advanced: metadata entries

This library can recognise metadata on the result stream in the following form:
{
  "head": { "vars": [ "book", "library" ] },
  "results": {
    "bindings": [
      { "book": { "type": "uri", "value": "http://example.org/book/book1" }, "library": { "type": "uri", "value": "http://example.org/book/library1" } }
    ]
  },
  "metadata": { "httpRequests": 0 }
}

This metadata can be captured by listening to the "metadata" event:
sparqlJsonParser.parseJsonResultsStream(myStream)
    .on('metadata', (metadata: any) => console.log(metadata))
    .on('data', (bindings: IBindings) => console.log(bindings));

Note that this is not part of the SPARQL/JSON specification.

License

This software is written by Ruben Taelman.
This code is released under the MIT license.