State transitions are an important part of our problem space and should be modelled within our domain, Greg Young states in a recent presentation focusing on basic event sourcing and how CQRS fits in.
Complex Event Processing, CEP, can be very useful for problems that have to do with time e.g. querying over historical data when you want to correlate things that have happened at different times, Greg Young explained in a recent presentation.
Version 2.0 of the Event Store, (an Event Source based persistence engine), was released last week with support for security, allowing for lock down of the Event Store and setting up Access Control Lists on event streams. The Projections library is now in beta and more documentation has been added.
Greg Young, the lead architect behind the Event Store, recently talked about the Projections Library in the Event Store and how it can be used as a Read Model. In his presentation Greg explained what the Projections Library is, together with its main use cases. He also presented a number of examples of practical use.