Mark Grossman


June 1987

Document Type


Degree Name



Dept. of Computer Science and Engineering


Oregon Graduate Center


Task Interaction and Control System (TICS) models computer-assisted problem-solving as the decomposition of a problem into subtasks. TICS provides a declarative and executable specification of such a model through the use of Horn clause logic. The logic clearly expresses the assumptions and rules that control the composition and interaction of the predicates that solve the subtasks. The power of logic programming to represent a hierarchical search for task solutions is augmented in TICS by evaluable predicates. Evaluable predicates invoke external procedures that execute as concurrent processes and whose internals are hidden from TICS. Logic provides a rich framework to specify a space of ways to solve a problem. This approach differs from the use of non-declarative codes and scripts to manage tasks, which usually permit only a subset of the possible solutions. TICS promotes user-directed exploration. Logic does not inflict artificial orderings or dependencies among subtasks that are not present in the problem domain itself. The specific order to solve the subtasks is not dictated, the user's search being limited only by those constraints inherent in the task and not by the rigidity of a computer program. TICS encourages trial-and-error problem-solving by carefully tracking true subtask dependencies, and minimally undoing previous work through the use of intelligent backtracking. TICS supports multiple techniques to cope with the need to undo side-effects. A prototype system was implemented in C++. Using this system to solve problems we noted that freedom from artificial constraints sometimes created a burden of choices. TICS was enhanced to provide a flexible means to limit the number of decisions that an end-user must consider. To guide decisions, a natural language format and menu facility were incorporated to communicate with the user. The versatility of the TICS framework is illustrated through example problems that have been implemented on our prototype system. We conclude by discussing our experience with TICS and topics for further research.





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