This paper presents an approach to the specification and validation of transactional business software. The focus of this work is on the production of detailed use case specifications and on the precise definition of all transactions and business rules using a subset of UML diagrams combined with textual specifications written in OCL (Object Constraint Language). We show how to produce and validate such artifacts using a scenario driven approach combined with animation and prototyping techniques in a highly iterative process. The paper also presents PSW (Precise Specification Workbench), a tool that supports the proposed approach.