We propose a new mechanism for implementing the elec- tronic shopping cart system (shortly, the shopping cart sys- tem) on the World Wide Web system (the Web system). The electronic shopping cart system is one of typical client- server systems, and it includes essential tasks to be imple- mented in the typical Web based client-server system. The most important task is to maintain context data between suc- cessive user sessions. Although several methods, which can be applied to im- plement the electronic shopping cart on the Web system, have been proposed, any of them can not attain the task of maintaining context data sufficiently. In this paper we analyze the task and point out the following three difficul- ties (d1) reliability, (d2) safety, and (d3) session manage- ment. We then propose a new mechanism (called the Con- text Data Storing (CDS) mechanism) to solve all of (d1), (d2) and (d3). In the proposed CDS mechanism, the context data for the session management is stored in the main memory of the client computer. As a result, the CDS mechanism can achieve both high reliability and high safety as well as the management capability of user sessions. Next, we use component object technology to implement the CDS mechanism. Then, we compared the performance of the electronic shopping cart system using the proposed CDS mechanism with the one using the previous methods. The result showed that our proposed mechanism has solved all difficulties (d1), (d2) and (d3) and has attained efficient communications between clients and Web servers.