Logos-TCS: an expert system language for operations management based on temporal constraint satisfaction

It is shown that the precedence graph upon which popular analysis tools in operations management such as PERT/CPM depend, is a special case of the temporal constraint satisfaction (TCS) problem. TCS provides a richer set of temporal relationships than the precedence relationship. A temporal constraint system provides a metaphor (constraint propagation) to model the down-line effects of perturbations that occur in dynamic operations. Logos-TCS, as a language to express expert problem-solving, provides a declarative framework to define TCS problems, Logos-TCS implements an innovative scheme by embedding a constraint system within a deductive reasoning system (Logos). Encoding expertise in relaxation strategies when constraint violations occur (situations arise that cause current operations to fail) is discussed. Heuristics such as task rearrangement, priority changes, first in first out, shifting start or finish times and retracting constraints have been the major source of expertise accumulated through experience. Logos-TCS provides a simple and straightforward rule-based framework to encode these strategies in its reasoning rules