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Graph database JS style for Node.js and the Browser. Built upon LevelUp and LevelDB.

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README.md

LevelGraph

Logo

NPM

NPM

LevelGraph is a Graph Database. Unlike many other graph database, LevelGraph is built on the uber-fast key-value store LevelDB through the powerful LevelUp library. You can use it inside your node.js application or in any IndexedDB-powered Browser. PhoneGap support coming soon (late fall).

LevelGraph loosely follows the Hexastore approach as presente in the article: Hexastore: sextuple indexing for semantic web data management C Weiss, P Karras, A Bernstein - Proceedings of the VLDB Endowment, 2008. Following this approach, LevelGraph uses six indices for every triple, in order to access them as fast as it is possible.

Build Status browser support

LevelGraph is an OPEN Open Source Project, see the Contributing section to find out what this means.

Install on Node.js

npm install levelgraph --save

At the moment it requires node v0.10.x, but the port to node v0.8.x should be straighforward. If you need it, just open a pull request.

Install in the Browser

Just download levelgraph.min.js and you are done!

Usage

The LevelGraph API remains the same for Node.js and the browsers, however the initialization change slightly.

Initializing a database is very easy:

var levelgraph = require("levelgraph"); // not needed in the Browser
var db = levelgraph("yourdb");

Get and Put

Inserting a triple in the database is extremey easy:

var triple = { subject: "a", predicate: "b", object: "c" };
db.put(triple, function(err) {
  // do something after the triple is inserted
});

Retrieving it through pattern-matching is extremely easy:

db.get({ subject: "a" }, function(err, list) {
  expect(list).to.eql([triple]);
  done();
});

It even support a Stream interface:

var stream = db.getStream({ predicate: "b" });
stream.on("data", function(data) {
  expect(data).to.eql(triple);
});
stream.on("end", done);

Triple Properties

LevelGraph support adding properties to triples with very little overhead (a part from storage costs), it is very easy:

var triple = { subject: "a", predicate: "b", object: "c", "someStuff": 42 };
db.put(triple, function() {
  db.get({ subject: "a" }, function(err, list) {
    expect(list).to.eql([triple]);
  });
});

Multiple Puts

LevelGraph also supports adding putting multiple triples:

var triple1 = { subject: "a1", predicate: "b", object: "c" };
var triple2 = { subject: "a2", predicate: "b", object: "d" };
db.put([triple1, triple2],  function(err) {
  // do something after the triples are inserted
});

Joins

LevelGraph also supports joins:

db.put([{
  subject: "matteo",
  predicate: "friend",
  object: "daniele"
}, {
  subject: "daniele",
  predicate: "friend",
  object: "matteo"
}, {
  subject: "daniele",
  predicate: "friend",
  object: "marco"
}, {
  subject: "lucio",
  predicate: "friend",
  object: "matteo"
}, {
  subject: "lucio",
  predicate: "friend",
  object: "marco"
}, {
  subject: "marco",
  predicate: "friend",
  object: "davide"
}], function () {

  var stream = db.joinStream([{
    subject: "matteo",
    predicate: "friend",
    object: db.v("x")
  }, {
    subject: db.v("x"),
    predicate: "friend",
    object: db.v("y")
  }, {
    subject: db.v("y"),
    predicate: "friend",
    object: "davide"
  }]);

  stream.on("data", function(data) {
    // this will print "{ x: 'daniele', y: 'marco' }"
    console.log(data);
  });
});

It also support a similar API without streams:

db.put([{
 ...
}], function () {

  db.join([{
    subject: "matteo",
    predicate: "friend",
    object: db.v("x")
  }, {
    subject: db.v("x"),
    predicate: "friend",
    object: db.v("y")
  }, {
    subject: db.v("y"),
    predicate: "friend",
    object: "davide"
  }], function(err, results) {
    // this will print "[{ x: 'daniele', y: 'marco' }]"
    console.log(results);
  });
});

It also allows to generate a stream of triples, instead of a context:

  db.join([{
    subject: db.v("a"),
    predicate: "friend",
    object: db.v("x")
  }, {
    subject: db.v("x"),
    predicate: "friend",
    object: db.v("y")
  }, {
    subject: db.v("y"),
    predicate: "friend",
    object: db.v("b")
  }], {
    materialized: {
      subject: db.v("a"),
      predicate: "friend-of-a-friend",
      object: db.v("b")
    }
  }, function(err, results) {
    // this will print all the 'friend of a friend triples..'
    // like so: { 
    //   subject: "lucio", 
    //   predicate: "friend-of-a-friend",
    //   object: "daniele"
    // }
  });

Deleting

Deleting is easy too:

var triple = { subject: "a", predicate: "b", object: "c" };
db.del(triple, function(err) {
  // do something after the triple is deleted
});

Navigator API

The Navigator API is a fluent API for LevelGraph, loosely inspired by Gremlin It allows to specify joins in a much more compact way and navigate between vertexes in our graph.

Here is an example, using the same dataset as before:

    db.nav("matteo").archIn("friend").archOut("friend").
      contexts(function(err, results) {
      // prints:
      // [ { x0: 'daniele', x1: 'marco' },
      //   { x0: 'daniele', x1: 'matteo' },
      //   { x0: 'lucio', x1: 'marco' },
      //   { x0: 'lucio', x1: 'matteo' } ]
      console.log(results);
    });

The above example match the same triples of:

    db.join([{
      subject: db.v("x0"),
      predicate: 'friend',
      object: 'matteo'
    }, {
      subject: db.v("x0"),
      predicate: 'friend',
      object: db.v("x1")
    }], function(err, results) {
      // prints:
      // [ { x0: 'daniele', x1: 'marco' },
      //   { x0: 'daniele', x1: 'matteo' },
      //   { x0: 'lucio', x1: 'marco' },
      //   { x0: 'lucio', x1: 'matteo' } ]
      console.log(results);
    });

It allows to see just the last reached vertex:

    db.nav("matteo").archIn("friend").archOut("friend").
      values(function(err, results) {
      // prints [ 'marco', 'matteo' ]
      console.log(results);
    });

Variable names can also be specified, like so:

db.nav("marco").archIn("friend").as("a").archOut("friend").archOut("friend").as("a").
      contexts(function(err, friends) {

  console.log(friends); // will print [{ a: "daniele" }]
});

Variables can also be bound to a specific value, like so:

db.nav("matteo").archIn("friend").bind("lucio").archOut("friend").bind("marco").
      values(function(err, friends) {
  console.log(friends); // this will print ['marco']
});

A materialized join can also be produced, like so:

db.nav("matteo").archOut("friend").bind("lucio").archOut("friend").bind("marco").
      triples({:
        materialized: {
        subject: db.v("a"),
        predicate: "friend-of-a-friend",
        object: db.v("b")
      }
    }, function(err, results) {

  // this will return all the 'friend of a friend triples..'
  // like so: { 
  //   subject: "lucio", 
  //   predicate: "friend-of-a-friend",
  //   object: "daniele"
  // }

  console.log(results); 
});

It is also possible to change the current vertex:

db.nav("marco").archIn("friend").as("a").go("matteo").archOut("friend").as("b").
      contexts(function(err, contexts) {

   //  contexs is: [{
   //    a: "daniele",
   //    b: "daniele"
   //   }, {
   //     a: "lucio", 
   //     b: "daniele"
   //   }]

});

Putting and Deleting through Streams

It is also possible to put or del triples from the store using a Stream2 interface:

var t1 = { subject: "a", predicate: "b", object: "c" };
var t2 = { subject: "a", predicate: "b", object: "d" };
var stream = db.putStream();

stream.write(t1);
stream.end(t2);

stream.on("close", function() {
  // do something, the writes are done
});

LevelUp integration

LevelGraph allows to leverage the full power of all LevelUp plugins.

Initializing a database with LevelUp support is very easy:

var levelup = require("level");
var levelgraph = require("levelgraph");
var db = levelgraph(levelup("yourdb"));

Browserify

You can use browserify to bundle your module and all the dependencies, including levelgraph, into a single script-tag friendly js file for use in webpages. For the convenience of people unfamiliar with browserify, a pre-bundled version of levelgraph is included in the build folder.

Simply require("levelgraph") in your browser modules and use level.js instead of level:

var levelgraph = require("levelgraph");
var leveljs = require("level-js");
var levelup = require("levelup");
var factory = function (location) { return new leveljs(location) };

var db = levelgraph(levelup("yourdb", { db: factory }));

Testling

Follow the Testling install instructions and run testling in the levelgraph directory to run the test suite against a headless browser using level.js

RDF support

LevelGraph does not support out of the box loading serialized RDF or storing it. Such functionality is provided by extensions:

Extensions

You can use multiple extensions at the same time. Just check if one depends on another one to nest them in correct order! (LevelGraph-N3 and LevelGraph-JSONLD are independent)

var lg = require('levelgraph');
var lgN3 = require('levelgraph-n3');
var lgJSONLD = require('levelgraph-jsonld');

var db = lgJSONLD(lgN3(lg("yourdb")));
// gives same result as
var db = lgN3(lgJSONLD(lg("yourdb")));

TODO

There are plenty of things that this library is missing. If you feel you want a feature added, just do it and submit a pull-request.

Here are some ideas:

  • [x] Return the matching triples in the JOIN results.
  • [x] Support for Query Planning in JOIN.
  • [x] Added a Sort-Join algorithm.
  • [ ] Add more database operators (grouping, filtering).
  • [x] Browser support #10
  • [ ] Live Joins #3
  • Extensions
    • [ ] RDFa
    • [ ] RDF/XML
    • [ ] Microdata

Contributing

LevelGraph is an OPEN Open Source Project. This means that:

Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.

See the CONTRIBUTING.md file for more details.

Credits

LevelGraph builds on the excellent work on both the LevelUp community and the LevelDB and Snappy teams from Google and additional contributors. LevelDB and Snappy are both issued under the New BSD Licence.

Contributors

LevelGraph is only possible due to the excellent work of the following contributors:

Matteo Collina GitHub/mcollina Twitter/@matteocollina
Jeremy Taylor GitHub/jez0990

LICENSE - "MIT License"

Copyright (c) 2013 Matteo Collina (http://matteocollina.com) and LevelGraph Contributors

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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