On the Computation of Natural Observers in Discrete-Event Systems
2010 (English)In: Discrete event dynamic systems, ISSN 0924-6703, E-ISSN 1573-7594, Vol. 20, no 1, 63-102 p.Article in journal (Refereed) Published
Natural projections with the observer property have proved effective in reducing the computational complexity of nonblocking supervisory control design, and the state sizes of the resulting controllers. In this paper we present an algorithm to verify this property, or if necessary to achieve it. A natural projection is a special type of general causal reporter map; for the latter an algorithm is already known for verification and modification. This algorithm could be used to verify the observer property of a natural projection, but if the natural projection is not an observer the algorithm is not applicable to modify it to an observer. Also, while a general reporter map always admits a unique smallest refinement with the observer property, a natural projection does not. Indeed there may exist several minimal extensions to the original observable event set of a natural projection. We show that the problem of finding a minimal extension is NP-hard, but propose a polynomial-time algorithm that always finds an acceptable extension. While not guaranteed to be minimal, it is in practice often reasonably small.
Place, publisher, year, edition, pages
2010. Vol. 20, no 1, 63-102 p.
Discrete-event systems, Model abstraction, Observer, Natural projection
IdentifiersURN: urn:nbn:se:kth:diva-28846DOI: 10.1007/s10626-008-0054-3ISI: 000274385100005ScopusID: 2-s2.0-76649129040OAI: oai:DiVA.org:kth-28846DiVA: diva2:396825
QC 201102112011-02-112011-01-212011-02-11Bibliographically approved