Algorithm = logic + control

The notion that computation = controlled deduction was first proposed by Pay Hayes 19 and more recently by Bibel 2 and Vaughn-Pratt 31. A similar thesis that database systems should be regarded as consisting of a relational component, which defines the logic of the data, and a control component, which stores and retrieves it, has been successfully argued by Codd 10. Hewitt's argument 20 for the programming language PLANNER, though generally regarded as an argument against logic, can also be regarded as an argument for the thesis that algorithms be regarded as consisting of both logic and control components. In this paper we shall explore some of the useful consequences of that thesis.