graphdb.js

A GraphDB and RDF4J data access library written in JavaScript to be used in Node.js.

Installation

Make sure you have Node.js version 8 or greater and Node Package Manager (npm) installed before start working with the library.

Currently the library is not published in NPM registry, but it still can be installed directly from this GitHub repository.

npm install --save Ontotext-AD/graphdb.js

Development

Setup Environment

• Checkout or clone the project.
• Make sure prerequisites are covered: node js and npm must be present and versions should be supported.
• Enter the project directory and execute

npm install

Running Tests

After any change the tests should be run and check if any existing functionality is not broken in result.

npm run test

or constantly watching for changes in source files and tests and re-execute the test suite

npm run test:watch

The best and preferred way a new feature or changes to be introduced is a test case to be written first and then the change to be implemented following the TDD approach.

Checking the codestyle

The library uses Google style in conjunction with ESLint's recommended ruleset.

npm run lint

Testing the packaging

Library is managed by NPM package manager. During publishing npm consults the .gitignore, .npmignore and package.json#files property in order to decide which resources should be published. If any change in the project structure, .gitignore or .npmignore is made, then publishing must be verified in order to be guaranteed that needed sources will be properly published. The packaging could be verified using the npm package command which generates a *.tgz archive in the project root. The archive should contain only the needed resources. Furture the archive could be used as a source for npm install where the path pointing the archive is provided.

Production build

The library is written in ES2016. During the build process source files src/ are transpiled to ES2015 and copied to lib/ directory.

A typescript definition file types.d.ts is generated in the lib/ as well.

Documentation is generated in docs/ from the JSDoc annotations in the source code.

npm run build

Prerequisites

Node >= 8.16

Usage

ServerClient

The ServerClient deals with operations on server level like obtaining a list with available repositories, concrete repository or deleting repositories. In order to work with the ServerClient it should be configured ServerClientConfig first.

• Configure ServerClient

const {ServerClient, ServerClientConfig} = require('graphdbjs').server;
const {RDFMimeType} = require('graphdbjs').http;

const serverConfig = new ServerClientConfig('http://rdf4j-compliant-server/', 0, {
    'Accept': RDFMimeType.SPARQL_RESULTS_JSON
});
const server = new ServerClient(serverConfig);

• Fetch repository ids

server.getRepositoryIDs().then(ids => {
    // work with ids
}).catch(err => console.log(err));

• Check if repository with given name exists

server.hasRepository('repository-name').then(exists => {
    if (exists) {
        // repository exists -> delete it for example
    }
}).catch(err => console.log(err));

• Delete repository with given name

server.deleteRepository('repository-name').then(() => {
    // successfully deleted
}).catch(err => console.log(err));

• Although a repository instance can be created using a constructor which can be seen in the examples below a client could obtain an instance of RDFRepositoryClient through the server client

server.getRepository('repository-name').then(repository => {
    // repository is a configured RDFRepositoryClient instance
}).catch(err => console.log(err));

RDFRepositoryClient

• Instantiating repository client

const readTimeout = 30000;
const writeTimeout = 30000;
const config = new RepositoryClientConfig(['http://GDB/repositories/my-repo'], {
  'Accept': RDFMimeType.TURTLE
}, '', readTimeout, writeTimeout);
const repository = new RDFRepositoryClient(config);

• Obtaining repository client instance through a ServerClient

const ServerClient = require('server/server-client');
const ServerClientConfig = require('server/server-client-config');
const RepositoryClientConfig = require('repository/repository-client-config')

const config = new ServerClientConfig('http://GDB', 0, {});
const server = new ServerClient(config);

const readTimeout = 30000;
const writeTimeout = 30000;
const repositoryClientConfig = new RepositoryClientConfig(['http://GDB/repositories/my-repo'], {}, '', readTimeout, writeTimeout);
return server.getRepository('automotive', repositoryClientConfig).then((rdfRepositoryClient) => {
// rdfRepositoryClient is a configured instance of RDFRepositoryClient
});

Reading

Statements could be fetched using the RDFRepositoryClient.get, RDFRepositoryClient.query, RDFRepositoryClient.download.

Every reading method can get the response parsed to data objects according to RDFJS data model specification (see Response Parsers).

• Reading statements

const payload = new GetStatementsPayload()
	.setResponseType(RDFMimeType.RDF_JSON)
	.setSubject('<http://eunis.eea.europa.eu/countries/AZ>')
	.setPredicate('<http://eunis.eea.europa.eu/rdf/schema.rdf#population>')
	.setObject('"7931000"^^http://www.w3.org/2001/XMLSchema#integer')
	.setContext('<http://example.org/graph3>')
	.setInference(true);

return repository.get(payload).then((data) => {
	// data contains requested staments in rdf json format
});

• Downloading data from repository by consuming a WritableStream

const dest = __dirname + '/statements.ttl';
const output = fs.createWriteStream(dest);
const payload = new GetStatementsPayload()
    .setResponseType(RDFMimeType.TURTLE)
    .get();
repository.download(payload).then((response) => {
    response.on('data', (chunk) => {
        output.write(new Buffer(chunk));
    });
    response.on('end', () => {
        output.end();
    });
});

• Query evaluation against a sparql endpoint

• SELECT query returning data objects

repository.registerParser(new SparqlXmlResultParser());

const payload = new GetQueryPayload()
  .setQuery('select * where {?s ?p ?o}')
  .setQueryType(QueryType.SELECT)
  .setResponseType(RDFMimeType.SPARQL_RESULTS_XML)
  .setLimit(100);

return repository.query(payload).then((stream) => {
  stream.on('data', (bindings) => {
    // the bindings stream converted to data objects with the registered parser
  });
  stream.on('end', () => {
    // handle end of the stream
  });
});

• ASK query returning a boolean result

const payload = new GetQueryPayload()
  .setQuery('ask {?s ?p ?o}')
  .setQueryType(QueryType.ASK)
  .setResponseType(RDFMimeType.BOOLEAN_RESULT);

repository.registerParser(new SparqlJsonResultParser());

return repository.query(payload).then((data) => {
  // data => true|false
});

Writing

• Uploading data in repository (POST) using ReadStream

const contentType = RDFMimeType.TURTLE;
const turtleFile = __dirname + '/statements.ttl';
fs.readFile(turtleFile, (err, stream) => {
    repository.upload(stream, null, null, contentType).catch((e) => console.log(e));
});

• Overwriting data in repository (PUT) using ReadStream

const contentType = RDFMimeType.TURTLE;
const file = __dirname + '/statements-overwrite.ttl';
fs.readFile(file, (err, stream) => {
    repository.overwrite(stream, null, null, contentType).catch((e) => console.log(e));
});

• Executing a sparql update query

const payload = new UpdateQueryPayload()
  .setQuery('INSERT {?s ?p ?o} WHERE {?s ?p ?o}')
  .setContentType(QueryContentType.X_WWW_FORM_URLENCODED)
  .setInference(true)
  .setTimeout(5);

return repository.update(payload).then(() => {
    // repository should have been updated at this point
});

Deleting

• Delete statement from given context

repository.deleteStatements(subj, pred, obj, contexts).then(() => {

});

Transactions

Repository operations can be executed in transaction. In order to work with transactions the TransactionalRepositoryClient must be used.

TODO

Reading

Writing

Deleting

Namespaces

TODO

Response Parsers

Read responses of different content types might be parsed to data objects with parsers registered in the repository instance.

The library provides a way parsers to be implemented and registered with given repository instance which in turn will use them to parse the response before returning it to the client.

Implementing a custom parser

A parser could be implemented by extending the ContentParser and implementing the parse and getSupportedType methods.

class RdfAsJsonParser extends ContentParser {
  getSupportedType() {
    return 'application/rdf+json';
  }

  parse(content) {
    // parse and return the content
    return parsedContent;
  }
}

The getSupportedType method must return one of the supported RDF and SPARQL MIME types this way defining that the parser is responsible for converting from that type.

Register parser in the repository

Parsers should be registered in the repository before executing any request.

// Import any of the predefined parsers
const {NTriplesParser} = require('graphdbjs').parser;
// And register it in the repository
repository.registerParser(new NTriplesParser());

Multiple parsers could be registered for different response types.

Registering a second parser for same content type results in overriding the previously registerted parser!

Predefined parsers

The library provides parsers for rdf formats using the N3 library:

• TurtleParser: text/turtle
• N3parser: text/rdf+n3
• NQuadsParser: text/x-nquads
• NTriplesParser: text/plain (N-Triples)
• TrigParser: application/x-trig

For SELECT query results in json and xml formats as well as boolean results from ASK queries following parsers are wrapped and exposed: sparqlxml-parse and sparqljson-parse

• SparqlXmlResultParser: application/sparql-results+xml, text/boolean
• SparqlJsonResultParser: application/sparql-results+json, text/boolean

License

LICENSE