Data Warehousing and OLAP over Big Data is becoming one of the emergent challenges for next-generation research, with special emphasis on data-intensive Cloud infrastructures. As a consequence, several studies are focusing the attention on this relevant issue, and various open problems arise. This evidence has inspired our study, which provide a comprehensive overview on actual open research problems in the context of Data Warehousing and OLAP over Big Data, along with a deep critical discussion on future research directions to be taken under this so-challenging road.
