  In Cyber Physical Systems humans are often kept in the loop as operators
and/or service users. Yet in many cases, humans and machines collaborate and
provide services to each other. Research on service models and service
composition for CPS exist; however, humans as service providers have not been
adequately considered as part of the CPS service composition model. We provide
a classification of human-as-a-service in CPS, and we propose a Service
Oriented Architecture (SOA) ontology model for the CPS environment as part of
the Everything-as-a-Service paradigm. The model considers human characteristics
and their dynamics, as a service provider or collaborator with the machine. As
the ontology model is an enabler for engineering a self-adaptive CPS with
human-machine collaboration as service providers, we describe how a commonly
used self-adaptive reference model can be refined to benefit from the vision.
We evaluate the ontological contribution against criteria that relates to
accuracy, completeness, adaptability, clarity, and consistency. We demonstrate
the feasibility of our conceptual reference model using a use case from the
medical domain and we show how human-machine service provision is possible.

Software Engineering