Today's first generation shopping agent is limited to comparing merchant offerings usually on price instead of their full range of attributes. Even in the full range comparison, there is not a good model which considers the overall features in the negotiation process. Therefore, the negotiation model needs to be extended to include negotiations over more attributes. We propose a negotiation model in agent-mediated electronic commerce to negotiate over prices, product features, warranties, and service policies based on utility theory and simple heuristics. We describe a prototype agent-mediated electronic commerce framework called Pmart. This framework provides the software reuse and extensibility based on object-oriented technology. It is implemented on Windows-based platforms using Java and CORBA for the network transparency and platform independence.