参考答案：system-structure

解析： J.R.Firth’s main approach to the notion of function in context was by means of concept system.People refer to his theory as system-structure theory. 弗尔斯构想根据语境功能这一概念来建立自己的语言学理论，而达到这一目的的主要途径是借助于系统概念。由于系统在他的理论中占据重要地位，所以他的理论被称为系统结构理论。