@abc.abstractmethod<EOL><INDENT>def is_linked(self):<DEDENT>
return<EOL>
Tests if this data element is linked to other data in the object.

        Updating linked data elements should refresh all metadata and
        revalidate object elements.

        :return: true if this element is linked, false if updates have no side effect
        :rtype: ``boolean``


        *compliance: mandatory -- This method must be implemented.*