CMP.12:1 - Problem frame

Use this when a calculation, rule language or program description has an intended meaning, but an effective way to execute it is missing, too costly or must change. You need to construct evaluation rules, translate the description into another executable form, or repair a translation that changes the result or behavior on which its user relies.

The reader can distinguish the admitted expressions and the operations they describe. The task is to turn those distinctions into an algorithm for evaluation or translation. Programs become inputs and outputs of that algorithm: a reader can examine how a rule is executed and change the rule’s representation without silently changing its use.

The result is an interpreter or effective translation, with the correspondence needed to use its output. Depending on the question, the preserved observation may include returned values, state changes, interaction, failure or termination. A compiler for a programming language, an evaluator for symbolic expressions and an interpreter for a decision language are different applications of this method.

Use an existing suitable evaluator or translator when it already provides the needed behavior affordably. Designing the notation’s useful distinctions is a separate question when those distinctions are still unknown. Choosing a physical realization follows the computational construction and its actual resource requirements.