Report Number: CS-TR-79-716
Institution: Stanford University, Department of Computer Science
Title: A framework for control in production systems
Author: Georgeff, Michael P.
Date: January 1979
Abstract: A formal model for representing control in production systems
is defined. The formalism allows control to be directly
specified independently of the conflict resolution scheme,
and thus allows the issues of control and nondeterminism to
be treated separately. Unlike previous approaches, it allows
control to be examined within a uniform and consistent
It is shown that the formalism provides a basis for
implementing control constructs which, unlike existing
schemes, retain all the properties desired of a knowledge
based system --- modularity, flexibility, extensibility and
explanatory capacity. Most importantly, it is shown that
these properties are not a function of the lack of control
constraints, but of the type of information allowed to
establish these constraints.
Within the formalism it is also possible to provide a
meaningful notion of the power of control constructs. This
enables the types of control required in production systems
to be examined and the capacity of various schemes to meet
these requirements to be determined.
Schemes for improving system efficiency and resolving
nondeterminism are examined, and devices for representing
such meta-level knowledge are described. In particular, the
objectification of control information is shown to provide a
better paradigm for problem solving and for talking about
problem solving. It is also shown that the notion of control
provides a basis for a theory of transformation of production
systems, and that this provides a uniform and consistent
approach to problems involving subgoal protection.