Extraction-Transformation-Loading (ETL) tools are pieces of software responsible for the extraction of data from several sources, their cleansing, customization and insertion into a data warehouse. In this paper, we delve into the logical design of ETL scenarios. We describe a framework for the declarative specification of ETL scenarios with two main characteristics: genericity and customization. Moreover, we present a palette of several templates, representing frequently used ETL activities along with their semantics and their interconnection. Finally, we discuss implementation issues and we present a graphical tool, ARKTOS II that facilitates the design of ETL scenarios, based on our model.