Generalized procedure calling and content-directed invocation

We suggest that the concept of a strategy can profitably be viewed as knowledge about how to select from among a set of plausibly useful knowledge sources, and explore the framework for knowledge organization which this implies. We describe meta rules, a means of encoding strategies that has been implemented in a program called TEIRESIAS, and explore their utility and contribution to problem solving performance. Meta rules are also considered in the broader context of a tool for programming. We show that they can be considered a medium for expressing the criteria for retrieval of knowledge sources in a program, and hence can be used to define control regimes. The utility of this as a programming mechanism is considered. Finally, we describe the technique of content-directed invocation used by meta rules, and consider its use as a way of implementing strategies. It is also considered in historical perspective as a knowledge source invocation technique, and its advantage over some existing mechanisms like goal-directed invocation is considered. This work was supported in part by the Bureau of Health Sciences Research and Evaluation of HEW under Grant HS-01544 and by the Advanced Research Projects Agency under ARPA Order 2494. It was carried out on the SUMEX Computer System, supported by the NIH under Grant RR-00785. The views expressed are solely those of the author.