conversion:subject is one of many conversion:Enhancements.

The conversion:Statement class can be used to assert triples that are not derived from input tabular data. The properties conversion:subject, conversion:predicate, and conversion:object are used to specify the corresponding elements of the triple to assert, and each may provide a template value (see Using template variables to construct new values).

Protege requires an assertion like the following in an instance file:

<https://localhost/special-path/part-another> a owl:Ontology .

      conversion:enhance [
         conversion:subject  "[/]special-path/part-[D]";
         conversion:predicate rdf:type;
         conversion:object    owl:Ontology;
      ];