Business Process (BP) improvement and alike require accurate descriptions of the BPs. We suggest to describe BPs as use case specifications. A use case specification comprises a description of the context of the BP, the interactions between the agents involved in the BP, the interactions of these agents with an automated system supporting the BP and attached system internal requirements. Constructing such specifications remains a difficult task. Our proposal is to use textual scenarios as inputs, describing fragments of the BP, and to guide, using a set of rules, their incremental production and integration in a use case specification also presented in a textual form. The paper presents the structure of a use case, the linguistic approach adopted for textual scenarios analysis and the guided process for constructing use case specifications from scenarios along with the guidelines and support rules grounding the process. The process is illustrated with a real case study borrowed to an Electricity Company.