Learn More
This paper is an overview of the current research on hierarchical control of discrete-event systems. Four major approaches are identified and described: bottom-up design, top-down design, state aggregation, and interface-based design. The research examined is grouped into these sections, in an attempt to unify the terminology and concepts where possible(More)
| The concept of observer was introduced in previous work by the authors on a hierarchical control theory of discrete-event systems (DES). It was shown that the observer property ensures that in a two-level hierarchy the low-level implementation of a nonblocking high-level supervisor is also nonblocking. In this paper we investigate the following problem:(More)
An abstract hierarchical control theory is developed lbr a class of timed discrete-event systems (TDES) within the discrete-event control architectural framework proposed earlier by the authors. For this development, a control theory for TDES is introduced in the spirit of a prior theory of Brandin. A notion of time control structures is introduced, and on(More)
Predicates are used extensively in modern database systems for purposes ranging from user specification of associative accesses to data, to user-invisible system control functions such as concurrency control and data distribution. Collections of predicates, or predicate files, must be maintained and accessed efficiently. This paper describes a dynamic(More)
Predicates are used extensively in modern data base systems, for purposes ranging from user specification of associative accesses to data, to user-invisible system control functions such as concurrency control and data distribution. Collections of predicates, or predicate files, must be maintained and accessed efficiently. This paper describes a dynamic(More)
This paper describes the development of a distributed knowledge-based system. A software system, namely Distributed Algorithmic and Rule-based Blackboard System (DARBS), was developed from its predecessor ARBS, which lacked the distributed computing feature. ARBS has been used in solving a number of engineering problems [1-3]. DARBS now utilises(More)