Why is my supervisor empty? Finding causes for the unreachability of states in synthesized supervisors

Abstract

Although supervisory control synthesis has been around for many years, adoption is still low. A weak point of synthesis is the absence of a reporting mechanism. When an empty or unexpected supervisor is returned, it is very difficult to explain why this is the case. It is desired to return an explanation for a question, like, "Why is my supervisor empty?". In general, the information needed to provide such an explanation is not present in the synthesized result.In this paper, causes (explanations) are generated for questions regarding the absence of behavior in the synthesized system. To this end, it is first investigated what information is needed and how it should be stored. Based on these findings, information of the influence of each requirement is encoded in the supervisor. This is done by annotating colors. The resulting so-called colored predicates can be used after synthesis to derive a cause for a given question.

Supervisory Controller Synthesis for Product Lines Using CIF 3

“…As a consequence, supervisory control synthesis may result in the impossibility to produce a supervisor, or lead to a controlled system that omits states of which the designer would not expect their omission. In recent work [43], the synthesis algorithm has been adapted to retrieve the reason why the controlled system is blocked from reaching specific states. This information can then be used for understanding which requirements (under which conditions) are conflicting, whereupon the model of the components and/or the requirement may be refined.…”