Module @incremunica/query-sparql-incremental

Incremunica SPARQL

Incremunica is an incremental SPARQL query engine build on top of comunica.

Install

$ npm install -g @incremunica/query-sparql-incremental

$ yarn add @incremunica/query-sparql-incremental

Usage

Incremunica can be used in JavaScript/TypeScript applications and from the command line.

Usage within application

This engine can be used in JavaScript/TypeScript applications as follows:

const QueryEngine = require('@incremunica/query-sparql-incremental').QueryEngine;
const isAddition = require('@incremunica/user-tools').isAddition;
const myEngine = new QueryEngine();

async function main() {
    const bindingsStream = await myEngine.queryBindings(`
    SELECT ?interest
    WHERE {
      <https://ruben.verborgh.org/profile/#me> foaf:topic_interest ?interest.
      <https://www.rubensworks.net/#me> foaf:topic_interest ?interest.
    }`, {
        sources: [
            "https://ruben.verborgh.org/profile/",
            "https://www.rubensworks.net/"
        ],
        pollingPeriod: 1, // Poll every second
    });

    // Consume results as a stream
    bindingsStream.on('data', (bindings) => {
        console.log("Is addition:", isAddition(bindings));

        console.log(bindings.toString()); // Quick way to print bindings for testing

        console.log("Has variable 'interest':", bindings.has('interest')); // Will be true

        // Obtaining values
        console.log(bindings.get('interest').value);
        console.log(bindings.get('interest').termType);
    });

    bindingsStream.on('end', () => {
        // The data-listener will not be called anymore once we get here.
    });
    bindingsStream.on('error', (error) => {
        console.error(error);
    });

    // As this is an incremental query engine, you need to end the query yourself otherwise it will keep checking for changes.
    setTimeout(() => bindingsStream.close(), 3000);
}

main();

To help develop with Incremunica we provide a collection of helper functions/classes in the @incremunica/user-tools package. The polling period is the time interval in seconds that the engine will check for changes in the data sources. The data event will be emitted whenever a new result is available, this result will be annotated as an addition or deletion. The end event will be emitted when the query is manually closed. Finally, the error event will be emitted when an error occurs during the query. This interface is similar to the one provided by the Comunica query-sparql package.

You can also use an incremental triple store. This store allows you to change the dataset (additions and deletions) and show you the changes in the query results.

const QueryEngine = require('@incremunica/query-sparql-incremental').QueryEngine;
const StreamingStore = require("@incremunica/streaming-store").StreamingStore;
const myEngine = new QueryEngine();
const streamingStore = new StreamingStore();

async function main() {
    streamingStore.import(quadStream);

    const bindingsStream = await myEngine.queryBindings(`
    SELECT *
    WHERE {
        ?s ?p ?o.
    }`, {
        sources: [ streamingStore ],
    });

    streamingStore.addQuad(quad);
    streamingStore.removeQuad(otherQuad);

    streamingStore.end();
}

main();

Usage from the command line

Show the help with all options:

$ comunica-sparql-incremental --help

Classes

QueryEngine
QueryEngineFactory