eCommerce of the Business-to-Business (B2B) type requires comprehensive contract negotiations depending entirely on a contract schema, which must be developed in advance. Contract schemas are modeled according to bill-of-materials. Undefined contract parts are not allowed (Closed World Assumption). In the focus of the discussions are implications, i.e. the contract parts are not independent of one another. Negotiations are conducted in question-answer and reasoning dialogs. A task-logic interpretation of propositional logic due to Kolmogorov is introduced. Contract schemas are specified by XML. It is suggested to implement contract negotiations on top of a modular workflow system.