function id2uri( id, options ) {
	var fopts;
	var opts;
	var keys;
	var err;
	var db;
	var i;
	if ( !isString( id ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be a string. Value: `%s`.', id ) );
	}
	opts = {
		'database': config.database
	};
	if ( arguments.length > 1 ) {
		err = validate( opts, options );
		if ( err ) {
			throw err;
		}
	}
	opts.database = resolve( cwd(), opts.database );
	fopts = {
		'encoding': 'utf8'
	};
	db = readJSON( opts.database, fopts );
	if ( instanceOf( db, Error ) ) {
		return db;
	}
	keys = objectKeys( db );
	for ( i = 0; i < keys.length; i++ ) {
		if ( db[ keys[i] ].id === id ) {
			return keys[ i ];
		}
	}
	return null;
}
Synchronously returns the URI corresponding to a provided id.

@param {string} id - id
@param {Options} [options] - options
@param {string} [options.database] - path to a link database file (JSON)
@throws {TypeError} must provide a string
@throws {TypeError} options argument must be an object
@throws {TypeError} must provide valid options
@returns {(Error|string|null)} result

@example
var uri = id2uri( 'bibtex' );
// returns 'http://www.bibtex.org/'