Over the last few years, several proposals have been presented for supporting conceptual and logical modelling of data warehousing populating processes - ETL processes. However, these processes usually have a high degree of specificity, which entails very complex data requirements and elaborate processing routines – often difficult to validate. In ETL process modelling, the use of the Alloy specification language introduces an innovative formalism to the traditional approaches, maintaining the flexibility for handling the specific behaviours of an ETL process. Additionally, Alloy specifications can be analysed and validated, offering greater confidence in its correctness, which is essential for the success of complex software products. In this paper we present and discuss how to specify and validate ETL processes - blocks of operations and their dependencies - using Alloy, inspired by advances in this area of research, which show the potential of using a formal language in the ETL process modelling domain.