The new generation of network computing seeks for organic integration of information resources and computing resources in the Internet, whereas most important of all is to deal with the open information in the Internet which acts as an open information system. The intension and extension of a concept as well as its dynamics, some basic definitions, operations and theorems is first studied, then a new formalization method of argumentation is presented, which emphasizes concept dynamics and argumentation phases. Based on these works, an argumentation system is developed.