This lecture represents the starting point for a series of three lectures about the topic query processing and parallel data processing in database systems. For that reason, it gives a general introduction of the topic. In the following lectures, we will focus more detailed on the aspects of query optimization and scheduling. We attached reading material for parallel data processing, as query processing is usually executed highly in parallel. The part about query execution and joining (as shown on the content slide) was already addressed in lecture week 3.