The approach presented here is quite different from the traditional view of logic programming. As Van Roy says (CTM p 640),[For a program] to have a logical semantics means that execution corresponds to deduction, i.e., that execution can be seen as performing inference and the result of procedure calls give valid tuples in a simple logical model, such as a model of the predicate calculus.In the view expressed here, execution is not deduction. Execution is asking whether a statement about to be executed is consistent with the set of statements already executed. If execution succeeds, the statement is consistent, and the new statement is added to the set of executed statements. If execution fails, computation along that path fails.Traditionally, one considers a logic program to be a collection of axioms and a computation to be deduction based on those axioms. This is a reductive process: can one reduce a query to a collection of ground clauses through the use of the axioms.
From our perspective, a program is not a collection of axioms. It is nothing other than the what any other program is: the _expression_ of the imagination of the programmer. As a program executes, the system checks to see if the statements that it encounters are consistent with each other. If so it continues; if not it fails. This is a creative rather than a reductive process.
What do you think of this? Right, wrong, boring? The complete page is here: http://cs.calstatela.edu/~wiki/index.php/Courses/CS_460/Fall_2005/Concurrent_logic_programming_in_Oz
-- Russ
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