I. Introduction
Traditional ETL (extract, transform, load) processes and their implementations stem from data warehouse approaches. Data are extracted from one or several source systems and then transformed into either an intermediate format (e.g. Parquet [13]) or into the format of the target system. After this transformation, when the data are in the adequate format, they are loaded into the target system. Still, current data ware-houses [20] [29] [7] offer possibilities to implement such ETL processes. But, although these implementations also include cloud-based capabilities, they often result in big monoliths.