GRAPH REDUCTION MODELS OF LOGIC PROGRAMMING CONTROL

对不确定程序控制的图化简模型的初步实验表明，这是一种可行和自然的方法。适用于AND和/或组合符的简化规则与一种新型的标记节点(ALT节点)一起，可以将声明性语言语句直接编译为图形部分，通过简单的重写规则进行简化将会影响回溯。逻辑语言的其他图形缩减方法将这一负担放在元语言上。操作图归约模型与声明性语言B的外延语义的匹配为扩展到全逻辑编程和未来结合更高级的控制结构提供了优雅的框架。虽然当前的模型通过显式地使用状态参数来抽象状态的复杂性，但在扩展中可以采用适当的替代策略。其他研究人员目前正在制作包含逻辑变量适当行为的图形归约模型，这将在我们的扩展中考虑。主要目标是开发当前模型，以正确高效地为声明性语言的复杂控件建模。对叠加Prolog‘s Cut的方法的调查已经在进行中。该模型将设法将必要的控制信息合并到图表中。简单的ALT节点在建模非确定性方面的成功是一个令人鼓舞的开始。

Initial experiments with a graph reduction model for nondeterministic program control indicate that this is a viable and natural approach. Appropriate reduction rules for and and or combinators together with a new type of tagged node (alt nodes) enable the straightforward compilation of declarative language statements to graph sections whose reduction by simple rewrite rules will effect backtracking. Other graph reduction approaches to logic languages place this burden on the metalanguage. The matching of an operational graph reduction model with a denotational semantics for the declarative language B provides an elegant framework for extension to full logic programming and the future incorporation of more advanced control structures. Although the current model abstracts the complexities of state by making explicit a state argument, there are appropriate alternative strategies that can be employed in the extension. Other investigators are currently producing graph reduction models incorporating appropriate behavior for logic variables, which will be considered in our extension. The main objective is to develop the current model to correctly and efficiently model sophisticated control for declarative languages. Investigation of methods to superimpose Prolog's cut is already underway. The model will seek ways to incorporate the necessary control information into the graph. The success of simple alt nodes in modeling nondeterminism is an encouraging start.