A fully connected Internet business environment will introduce a high level of dynamics to the business decision, and thus, information of various items may undergo constant changes. In addition, there could be a flood of similar shopping sites. In such a highly dynamic environment, ordinary online customers may feel that online shopping is not comfortable. Exisiting service models or systems cannot effectively reflect such a dynamic environment and support ordinary online customers. This paper describes a new ecommerce service called the CIGMA. The CIGMA provides catalog comparison and purchase mediation services over multiple shopping site for ordinary online customers. A key characteristic of the CIGMA is that the service is provided based on high performance catalog datebase caching. So, the CIGMA service can match the desire of the online sustomers for the fast response as well as provide high through-put to process internet-scale customers. This paper presents the system architecture and related issues; real-time update scheme and catalog conversion mechanism. Performance of the CIGMA is also evaluated based on a working prototype system.