Interface theories are employed in the component-based design of concurrent systems. They often emerge as combinations of Interface Automata (IA) and Modal Transition Systems (MTS), e.g., Nyman et al.’s IOMTS, Bauer et al.’s MIO, Raclet et al.’s MI or our MIA. In this paper, we generalise MI to
interfaces, for which we resolve the longstanding conflict between unspecified inputs being allowed in IA but forbidden in MTS. With this solution we achieve, in contrast to related work, an
parallel composition, a
preorder, a conjunction on interfaces with
supporting perspective-based specifications, and a quotienting operator for decomposing
specifications in a single theory.