This paper presents a novel approach to automated negotiation that is particularly suitable to open environments, such as the Internet. In this approach agents can negotiate in any type of marketplace regardless of the negotiation mechanism in use. In order to support a wide variety of negotiation mechanisms, protocols are no longer hardcoded in the agents participating to negotiations, but are now expressed in terms of a shared ontology, thus making this approach particularly suitable for applications such as electronic commerce. The paper describes the negotiation ontology and provides a walkthrough example describing how the approach based on the negotiation ontology could be applied to the trading agent competition scenario.