Digital Business Ecosystems (DBE) are the technical environment where business organisations can live. One important aspect of this type of ecosystem is the collaboration of its members. Successful negotiation processes between members are a fundamental requirement for sustainable collaboration. The contribution of this paper is a negotiation language specified by means of an open metamodel, which provides the basis for SMEs to collaborate within a DBE. The model is presented on the abstraction level of a Metamodel - in the MDA sense of the term - allowing it to be used in a variety of domains and application scenarios. This paper focuses on the introduction of the fundamental concepts of the Metamodel and details of the models it consists of, plus an initial validation by presenting a worked example.