You cannot, directly. You can either use some intermediate steps,
e.g first exporting your schema in some form (e.g. csv) that can be
then turned into Excel (you could look at things like  or ,
for example), and you use Cellfie  to import it, or you could try
to access the table describing the schema, if your database supports
it, and map it to triples using ontop, and then materialize those
triples either through the Ontop ->
Materialize triples... menu option or their command
line client .
If you can't make any of this work, you can use Protege 3.5 with the
latest version of the DataMaster plugin to create an OWL ontology
(do not create a Protege Frames ontology). Then load that OWL
ontology in Protege 5.