static public function getIndexById($identifier) {
        
        $indexClass = new core_kernel_classes_Class(OntologyIndex::RDF_TYPE);
        $resources = $indexClass->searchInstances(array(
            OntologyIndex::PROPERTY_INDEX_IDENTIFIER  => $identifier
            ),array('like' => false)
        );
        if (count($resources) > 1) {
            throw new \common_exception_InconsistentData("Several index exist with the identifier ".$identifier);
        }
        return count($resources) > 0
            ? new OntologyIndex(array_shift($resources))
            : null;
    }