Adding the R to CQS: some storage options

I've been writing quite a bit about CQS (or command and query separation) lately. In my last post on using events, I already hinted towards bringing in the R; command and query responsibility separation. With CQS, commands can mutate data, while queries can only read that data. CQRS takes this one step further, and assigns commands and queries each a dedicated model; we now talk of a write side, and a read side.