node-rdf2json.js

var http = require("http");
var sys = require("sys");
var RDF = require("../vendor/rdf-parser/parser").RDF;
var fs = require("fs");

function generateFlatRDFJSONString(triples) {
	var rdfjson = "";
	for ( var i = 0; i < triples.length; i++) {
		rdfjson += "{";
		var subject = triples[i].subject.toString();
		var predicate = triples[i].predicate.toString();
		var object = triples[i].object == undefined ? undefined
				: triples[i].object.toString();
		var lang = triples[i].lang ? triples[i].lang.toString() : "";
		var datatype = triples[i].datatype ? triples[i].datatype.toString()
				: "";
		if (triples[i].type == "resource") {
			rdfjson += "\"s\" : { \"type\" : \"uri\", \"uri\" : \"" + subject
					+ "\" },";
			rdfjson += "\"p\" : \"" + predicate + "\",";
			rdfjson += "\"o\" : { \"type\" : \"uri\", \"uri\" : \"" + object
					+ "\" }";
		} else {
			rdfjson += "\"s\" : { \"type\" : \"uri\", \"uri\" : \"" + subject
					+ "\" },";
			rdfjson += "\"p\" : \"" + predicate + "\",";
			rdfjson += "\"o\" : { \"type\" : \"literal\", \"val\" : \""
					+ object + "\" , \"lang\" : \"" + lang
					+ "\", \"datatype\" : \"" + datatype + "\"}";
		}
		if (i != (triples.length - 1)) {
			rdfjson += "},";
		} else {
			rdfjson += "}";
		}
	}
	return rdfjson;
}

function _toRDFJSON(rdf, type, callback) {
	var rdfjson = "";
	if (type.toLowerCase() == "flat") {
		var triples = rdf.Match(null, null, null, null);
		rdfjson += "{ \"data\" : [";
		rdfjson += generateFlatRDFJSONString(triples);
		rdfjson += "]}";
	} else if (type.toLowerCase() == "sparql") {
		var triples = rdf.Match(null, null, null, null);
		rdfjson += "{ \"head\" : { \"vars\" : [\"s\", \"p\", \"o\"]},";
		rdfjson += "\"results\" : { \"bindings\" : [";
		rdfjson += generateFlatRDFJSONString(triples);
		rdfjson += "]}}";
	} else if (type.toLowerCase() == "talis") {
		var triples = rdf.Match(null, null, null, null);
		sys.puts(sys.inspect(triples));
		var subjects = new Array();
		for ( var i = 0; i < triples.length; i++) {
			if (subjects.indexOf(triples[i].subject) != -1) {
				continue;
			} else {
				subjects.push(triples[i].subject);
			}
		}
		rdfjson += "{";
		for ( var i = 0; i < subjects.length; i++) {
			rdfjson += " \"" + subjects[i] + "\" : {";
			var groupSubjects = rdf.Match(null, subjects[i], null, null);
			var predicates = new Array();
			for ( var j = 0; j < groupSubjects.length; j++) {
				if (predicates.indexOf(groupSubjects[j].predicate) != -1) {
					continue;
				} else {
					predicates.push(groupSubjects[j].predicate);
				}
			}
			for ( var j = 0; j < predicates.length; j++) {
				rdfjson += "\"" + predicates[j] + "\" : [";
				groupObjects = rdf
						.Match(null, subjects[i], predicates[j], null);
				for ( var k = 0; k < groupObjects.length; k++) {
					var object = groupObjects[k].object;
					if (!groupObjects[k].type)
						continue;// TODO If the parsing result is correct,
									// each statement should always have this
									// type info.
					if (groupObjects[k].type.toString() == "literal") {
						rdfjson += "{ \"value\" : \"" + object.toString()
								+ "\", \"type\" : \"uri\"";
						if (groupObjects[k].datatype) {
							rdfjson += ", \"datatype\" : \""
									+ groupObjects[k].datatype.toString()
									+ "\"";
						}
						if (groupObjects[k].lang) {
							rdfjson += ", \"lang\" : \""
									+ groupObjects[k].lang.toString() + "\"";
						}
						rdfjson += "}";
					} else if (groupObjects[k].type.toString() == "resource") {
						if (object.toString().substr(0, 2) == "_:n") {
							rdfjson += "{ \"value\" : \"" + object.toString()
									+ "\", \"type\" : \"bnode\"}";
						} else {
							rdfjson += "{ \"value\" : \"" + object.toString()
									+ "\", \"type\" : \"uri\"}";
						}
					}
					if (k < groupObjects.length - 1) {
						rdfjson += ",";
					}
				}
				rdfjson += "]";
				if (j < predicates.length - 1)
					rdfjson += ",";
			}
			rdfjson += "}";
			if (i < subjects.length - 1)
				rdfjson += ",";
		}
		rdfjson += "}";
	}
	callback(null, rdfjson);
}

exports.convertStringIntoRDFJSON = function(rdfxml, type, callback) {
	var rdf = new RDF();
	rdf.loadRDFXML(rdfxml);
	_toRDFJSON(rdf, type, function(err, rdfjson) {
		callback(null, rdfjson);
	});
};

exports.convertFileIntoRDFJSON = function(filepath, type, callback) {
	var self = this;
	var rdf = new RDF();
	fs.readFile(filepath, function(err, data) {
		self.convertStringIntoRDFJSON(data, type, function(err, rdfjson) {
			callback(null, rdfjson);
		});
	});
};

exports.convertURLIntoRDFJSON = function(url, type, callback) {
	var rdf = new RDF();
	rdf.getRDFURL(url, function() {
		_toRDFJSON(rdf, type, function(err, rdfjson) {
			callback(null, rdfjson);
		});
	});
};