Negotiating with suppliers and with customers is a key part of supply chain management. However, with recent technological advances, the mechanisms available to carry out such activities have become increasingly sophisticated, and the environment in which these activities take place has become highly dynamic. As a consequence, the overall planning of these complex trades, and the coordination of the various component activities, need to be carefully considered. In this setting, it is crucial that the intended behaviour, and through that, the desired outcomes, of these composite trading activities be expressed in a suitably precise manner. Using an approach based on the generation of negotiation plans, this paper describes (i) an approach to the specification of such complex activities, and (ii) a corresponding execution model. The proposal is illustrated and validated by means of a scenario taken from a recent trading agent competition.