Events and queries

One thing that I've heard many times when talking about event sourcing with developers who are new to this technique, is the claim that event sourcing is not suitable for reporting. Let's first define what reporting is. Normally, we think of it as the ability to retrieve the system state from the database on demand, using filters and grouping, with minimal latency. Relational databases are quite good for this purpose since this was the main reason that relational databases were invented in the first place. If you are old enough, you might remember a short period of hype around object databases (ODBMSes, short for object-oriented database management system) in the mid-1990s. What could be better than storing entire objects to a database, without taking care of the impedance mismatch? In a world that is largely dominated by different kinds of relational...