  Recent regulations, such as the European General Data Protection Regulation
(GDPR), put stringent constraints on the handling of personal data. Privacy,
like security, is a non-functional property, yet most software design tools are
focused on functional aspects, using for instance Data Flow Diagrams (DFDs). In
previous work, a conceptual model was introduced where DFDs could be extended
into so-called Privacy-Aware Data Flow Diagrams (PA-DFDs) with the aim of
adding specific privacy checks to existing DFDs. In this paper, we provide an
explicit algorithm and a proof-of-concept implementation to transform DFDs into
PA-DFDs. Our tool assists software engineers in the critical but error-prone
task of systematically inserting privacy checks during design (they are
automatically added by our tool) while still allowing them to inspect and edit
the. PA-DFD if necessary. We have also identified and addressed ambiguities and
inaccuracies in the high-level transformation proposed in previous work. We
apply our approach to two realistic applications from the construction and
online retail sectors.
