Visual Programming Languages have been widely adopted in design and comprehension of sophisticated systems. Context-sensitive graph grammar formalisms are suitable tools for specifying these languages, since they are intuitive and possess sufficient expressive power and usability. Nevertheless, some of the formalisms whose contexts are implicitly or incompletely represented in productions, called implicit context-sensitive graph grammars, suffer inherent weakness in intuitiveness and limitations in parsing algorithms. To address these issues, this paper formally presents a notion of context on the underlying concepts of partial and total precedence relations, characterizes their fundamental properties, and establishes a connection between contexts and their instances (also called context graphs elsewhere), based on the Reserved Graph Grammar formalism, a representative of implicit graph grammars. Moreover, three typical applications of contexts are illustrated, which show that contexts can both facilitate the comprehension and design of implicit graph grammars so as to enhance their intuitiveness, and make the existent efficient parsing algorithms more widely applicable.

视觉编程语言已被广泛用于复杂系统的设计和理解中。上下文相关的图文法形式主义是用于指定这些语言的合适工具，因为它们直观且具有足够的表达能力和可用性。但是，某些在上下文中隐式或不完整地表示形式的形式主义（称为隐式上下文敏感图文法）在直观性和解析算法方面存在固有的弱点。为了解决这些问题，本文正式提出了关于部分优先权和全部优先权关系的基本概念的上下文概念，描述了它们的基本属性，并在上下文及其实例之间建立了联系（在其他地方也称为上下文图），基于保留图语法形式主义，即隐式图语法的代表。此外，还说明了上下文的三种典型应用，它们表明上下文既可以促进对隐式图文法的理解和设计，从而提高其直观性，又可以使现有的高效解析算法得到更广泛的应用。