  Motivated by the Model-Based Design process for Cyber-Physical Systems, we
consider issues in conformance testing of systems. Conformance is a
quantitative notion of similarity between the output trajectories of systems,
which considers both temporal and spatial aspects of the outputs. Previous work
developed algorithms for computing the conformance degree between two systems,
and demonstrated how formal verification results for one system can be re-used
for a system that is conformant to it. In this paper, we study the relation
between conformance and a generalized approximate simulation relation for the
class of Open Metric Transition Systems (OMTS). This allows us to prove a
small-gain theorem for OMTS, which gives sufficient conditions under which the
feedback interconnection of systems respects the conformance relation, thus
allowing the building of more complex systems from conformant components.
