An increasing number of social computational systems consist of a great amount of autonomous entities and operate in highly dynamic and unpredictable environments. To construct such systems needs to seek high-level abstrac- tion to manage the complexity of the systems and novel mechanism to support their characteristics, i.e., dynamism and flexibility. Agent-oriented programming （AOP） is con- sidered as a potential paradigm for developing such systems by exhibiting a number of characteristics, such as autonomy, flexibility, social ability, etc. However, current researches on AOP mainly focus on the construction of multi-agent system （MAS） with theory and language facilities inspired from arti- ficial intelligence （AI） and distributed AI, seldom considering and integrating the proven principles and practices of pro- gramming and software engineering. Moreover, abstractions and mechanism based on AI are inadequate for developing dynamic and flexible MAS in open environment. This paper proposes a novel AOP approach, namely Oragent, for con- structing and implementing dynamic and flexible systems. From a software engineering perspective, Oragent integrates organizational concepts and mechanism into AOP language, and support the dynamism and flexibility with explicit prim- itives. The proposed approach consists of a programming model and a corresponding programming language. This paper presents the syntax and formal operational semanticsof Oragent language, and studies a case to demonstrate our approach.
