def ensure_default_namespace(self) -> Namespace:
        """Get or create the BEL default namespace."""
        namespace = self.get_namespace_by_keyword_version(BEL_DEFAULT_NAMESPACE, BEL_DEFAULT_NAMESPACE_VERSION)

        if namespace is None:
            namespace = Namespace(
                name='BEL Default Namespace',
                contact='charles.hoyt@scai.fraunhofer.de',
                keyword=BEL_DEFAULT_NAMESPACE,
                version=BEL_DEFAULT_NAMESPACE_VERSION,
                url=BEL_DEFAULT_NAMESPACE_URL,
            )

            for name in set(chain(pmod_mappings, gmod_mappings, activity_mapping, compartment_mapping)):
                entry = NamespaceEntry(name=name, namespace=namespace)
                self.session.add(entry)

            self.session.add(namespace)
            self.session.commit()

        return namespace
Get or create the BEL default namespace.