rdf

##The Jassa RDF module

Introduction

This module, which is part of the "JAscript Suite for Sparql Access (Jassa)", contains core RDF classes which can serve as a solid foundation for JavaScript-based Semantic Web libraries and applications. The design of this module follows closely the one of the Apache Jena Java project.

Architecture

Jassa uses prototype.js's Class object which offers a high level abstraction for the definition of interfaces and the creation of inheritance hierarchies.

Usage

All classes reside in the rdf namespace of the Jassa object:

<!-- Required libraries -->
<script src="jquery.js"></script>
<script src="underscore.js"></script>
<script src="underscore.string.js"></script>
<script src="prototype.js"></script>

<script src="jassa.js"></script>
...
var rdf = Jassa.rdf;

Example usage of the rdf and vocab modules

The rdf module holds core RDF classes which are similar to those of Jena. The vocab module defines the following vocabularies (work in progress):

• xsd
• rdf
• rdfs
• owl
• wgs84

These two modules depend on each other (and thus cannot be used separately), because the vocabulary is expressed in terms of rdf classes, however literals require the xsd vocabulary.

Example usage:

var rdf = jassa.rdf;
var vocab = jassa.vocab;

var s = rdf.NodeFactory.createVar("s");
var p = vocab.rdf.type;
var o = rdf.NodeFactory.createUri("http://example.org/ontology/MyClass");

var triple = new rdf.Triple(s, p, o);

console.log("Triple: " + triple);
console.log("Subject is a variable: " + triple.getSubject().isVariable());

Public API

The RDF module is based on the files rdf-core.js and rdf-literals.js. This separation exists because literals require the xsd vocabulary, whereas the xsd vocabulary is expressed using classes of rdf-core.js.

Note: Jena uses the spelling for 'URI', whereas Jassa uses the spelling 'Uri'.

• The Node hierarchy. This is the same hierarchy as used in Jena. Node is an interface with the concrete implementations Node_Blank, Node_Uri, Node_Literal, and Node_Variable. It is recommended to create instances of Node using the NodeFactory. In practice, one should only rely on the Node interface. In general, all methods below return the appropriate result for the node if applicable, otherwise they should die horribly.

• String getUri(): Returns the URI.

• String getName(): Returns the variable name.

• AnonId getBlankNodeId(): Returns the blank node it object (this object is only required to be comparable).

• String getBlankNodeLabel(): Returns a string representation of the blank node id

• LiteralLabel getLiteral(): Returns the LiteralLabelobject for literals. This object holdsvalue, lexicalForm, datatypeandlanguage, but is itself not bound to the Node` hierarchy.

• Object getLiteralValue(): Returns the object of the literal.

• String getLiteralLexicalForm(): Returns the lexical form of the literal.

• RdfDatatype getLiteralDatatype(): Returns the RDF Datatype object. RdfDatatype bundles a URI with a Object parse(String lexicalForm) and String unparse(Object value) methods.

• String getLiteralDatatypeUri(): Returns the URI of the RDF datatype.

• boolean isBlank(): true iff the node corresponds to a blank node.

• boolean isUri(): true iff the node corresponds to a URI.

• boolean isLiteral(): true iff the node corresponds to a literal.

• boolean isVariable(): true iff the node represents a variable.

• boolean equals(Node): Compares two nodes for equivalence.

• AnonId: Interface for blank node ids.

• AnonIdStr: Create an instance of an AnonId using var anonId = new rdf.AnonIdStr("myBlanknodeLabel");

• NodeFactory: This class provides a set of static methods for the creation of Node objects:

• Node createUri(String uri): Creates a new URI node

• Node createVar(String varName): Creates a new varible node

• Node createAnon(AnonId anonId): Creates a new blank node.

• Node createTypedLiteralFromValue(Object value, String typeUri): Creates a literal node. The value is unparsed to its lexical form according to typeUri.

• Node createTypedLiteralFromString(String value, String typeUri): Creates a literal node. The string is parsed to a JavaScript object according to typeUri`.