tpt / sparqljson-parse.js

Parses SPARQL JSON query results

SPARQL-Results+JSON Parse

A utility package that allows you to parse SPARQL JSON results in a convenient RDFJS-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" } }
    ]
  }
}

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') },
]

Where namedNode is an RDFJS named node.

This library automatically converts all SPARQL JSON result values to their respective RDFJS 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.

License

This software is written by Ruben Taelman.

This code is released under the MIT license.