  Privacy policies outline the data practices of Online Social Networks (OSN)
to comply with privacy regulations such as the EU-GDPR and CCPA. Several
ontologies for modeling privacy regulations, policies, and compliance have
emerged in recent years. However, they are limited in various ways: (1) they
specifically model what is required of privacy policies according to one
specific privacy regulation such as GDPR; (2) they provide taxonomies of
concepts but are not sufficiently axiomatized to afford automated reasoning
with them; and (3) they do not model data practices of privacy policies in
sufficient detail to allow assessing the transparency of policies. This paper
presents an OWL Ontology for Privacy Policies of OSNs, OPPO, that aims to fill
these gaps by formalizing detailed data practices from OSNS' privacy policies.
OPPO is grounded in BFO, IAO, OMRSE, and OBI, and its design is guided by the
use case of representing and reasoning over the content of OSNs' privacy
policies and evaluating policies' transparency in greater detail.
