  We address the problem of complying with the GDPR while processing and
transferring personal data on the web. For this purpose we introduce an
extensible profile of OWL2 for representing data protection policies. With this
language, a company's data usage policy can be checked for compliance with data
subjects' consent and with a formalized fragment of the GDPR by means of
subsumption queries. The outer structure of the policies is restricted in order
to make compliance checking highly scalable, as required when processing
high-frequency data streams or large data volumes. However, the vocabularies
for specifying policy properties can be chosen rather freely from expressive
Horn fragments of OWL2. We exploit IBQ reasoning to integrate specialized
reasoners for the policy language and the vocabulary's language. Our
experiments show that this approach significantly improves performance.
