rdf

RDF datatype integration, RDF Interfaces API, and utility functions

npm install rdf
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RDF Interfaces implementation for Node.js

An RDF Interfaces implementation in ECMAScript, designed for Node.js, to implement RDF datatypes with Javascript types and provide related APIs and in-memory utilities.

This implements:

See also:

Implementation largely adapted from webr3's js3, rdfa-api, and rdf-api implementations:

This is free and unencumbered software released into the public domain. For information, see http://unlicense.org/.

Usage

The ultimate documentation is the source code. The lib/rdf.js file should be especially useful.

RDFNode

rdf.Triple, rdf.RDFNode, rdf.BlankNode, rdf.Literal are implemented as defined under RDF Interfaces: Basic Node Types. Standard strings are used in place of NamedNode, and rdf.IRI is available for more complex manipulations of the URI structure.

IndexedGraph

An implementation of RDF Interfaces: Graph that stores triples in an Array. This is useful for quick inserts and iterating the complete list of triples.

TripletGraph

An implementation of RDF Interfaces: Graph with fast querying on any combination of subject, predicate, or object, using three indexes.

TurtleParser

An implementation of the Data parser API of RDF Interfaces.

var turtleParser = new rdf.TurtleParser(environment);
turtleParser.parse(turtle, callback, base, filter, graph);

Where:

  • environment is the optional RDF Environment that will resolve prefixes and create bnodes. If left out, a new, empty environment will be created. The enviornment is accessible from the environment property.
  • turtle is the document body to be processed.
  • callback is an optional function(Graph) to be called when processing is completed. This should normally be undefined, the parser is fully synchronous and processing is completed after the parse() function returns.
  • base is the base URI that relative URIs will be resolved against.
  • filter is an optional function(Triple) that will restrict which triples are added to the output graph. The function takes an input Triple and returns true to include the triple in the output graph.
  • graph is an optional Graph that triples will be add()ed to. If left out, a new IndexedGraph will be used.

Since @base and @prefix directives modify the environment passed to TurtleParser, it's recommended a new TurtleParser be used for each document.

RDF Environment

The RDF Environment is the context that bnodes are described relative to, and where namespaces/prefixes are defined. The API implements the RDF Environment API of RDF Interfaces.

The rdf module creates one such global environment by default, accessible at rdf.environment. Others are created where necessary, e.g. when parsing a Turtle document, and may be created using new rdf.RDFEnvironment.

Builtins

Instead of using NamedNode, URIs by default are represented as plain strings. The RDFNode interface may be overloaded onto the standard String object using rdf.setBuiltins() or onto a particular prototype by using:

rdf.setObjectProperties(Object.prototype);
rdf.setStringProperties(String.prototype);
rdf.setArrayProperties(Array.prototype);
rdf.setBooleanProperties(Boolean.prototype);
rdf.setDateProperties(Date.prototype);
rdf.setNumberProperties(Number.prototype);

as done in the setBuiltins function call in lib/Builtins.js.

This extends the prototype definitions to act as native RDF types as well, for example:

true.toNT();         // "true"^^<http://www.w3.org/2001/XMLSchema#boolean>
(12 * 1.4).toNT();   // "12.3"^^<http://www.w3.org/2001/XMLSchema#decimal>

Object Builtins

Any two values may be compared with each other using the equals method:

(true).equals(rdf.environment.createLiteral('true', null, 'xsd:boolean'.resolve()) // true

The node type may be queried with the nodeType method:

"_:bnode".nodeType()
"http://example.com/".nodeType()

An object may be assigned a URI and parsed for triples with the ref method:

var structure =
    { 'dbp:dateOfBirth': '1879-03-14'.tl('xsd:date')
    , 'foaf:depictation': 'http://en.wikipedia.org/wiki/Image:Albert_Einstein_Head.jpg'
    }.ref('dbr:Albert_Einstein');

ref may be called without any argument to create a BlankNode.

The resulting object has a number of methods:

  • structure.n3() returns a Turtle/N3 document close to the original structure.
  • structure.toNT() returns an N-Triples formatted list of triples.
  • structure.graphify() returns an IndexedGraph of triples.

If multiple properties with the same predicate need to be added, put the multiple values in an Array:

{a: ['foaf:Person']}.ref()

An Array may also be used to make an RDF Collection (linked list), with the toList method:

['rdfs:Class', 'rdfs:Resource'].toList()

String Builtins

Strings may be used in place of a NamedNode and BlankNode, and have the same properties. There are the following methods:

  • tl(type) creates a typed literal out of the given value.
  • l(lang) creates a standard literal, with an optional language value.
  • resolve() resolves a CURIE/term to an IRI. Unlike the enviornment/profile method, this returns the original string if unsuccessful (for instance, if the string is already a URI).

URIs passed to these functions may be CURIEs and are resolved with the global rdf.environment.

Tests

A vows test suite is found in the tests directory.

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