The purpose of the paper is to present our approach for specifying system behavior during analysis, part of the Fondue software development method. The approach is exempli ed on a case study, a Drink Vending Machine (DVM). It is based on Operation Schemas and a Protocol Model. The Protocol Model describes the tem- poral ordering of the system operations by an UML protocol statemachine. An Operation Schema describes the functionality of a system operation by pre- and postconditions; they are written in the Object Constraint Language (OCL), with a few amendments and extensions. Our approach o ers a middle ground between the informal descriptions of Use Cases and the solution-oriented models of object interaction in UML. We believe that declarative behavioral speci cation techniques, like the one proposed in this paper, lead to more con dence in the quality of the software because they allow one to reason about system properties.