The current Web technology is not suitable for representing knowledge nor sharing it among organizations over the Web. There is a rapidly increasing need for exchanging and linking knowledge over the Web, especially when several sellers and buyers come together on the Web to form a virtual marketplace. This paper explains an infrastructure that enables sharing of knowledge over the Web and thus effectively supports the formation of virtual marketplaces on the Web. The concept of an active virtual marketplace can be realized using this infrastructure and such an application has been developed.