CQRS, Event-Sourcing and Web-Applications

Hello,


As I am reading some CQRS resources, there is a recurrent point I do not
catch. For instance, let's say a client emits a command. This command is
integrated by the domain, so it can refresh its domain model (DM). On the
other hand, the command is persisted in an Event-Store. That is the most

common scenario.


1) When we say the DM is refreshed, I suppose data is persisted in the
underlying database (if any). Am I right ? Otherwise, we would deal with a
memory-transient model, which I suppose, would not be a good thing ? (state
is not supposed to remain in memory on server side outside a client
request).


2) If data is persisted, I suppose the read-model that relies on it is
automatically updated, as each client that requests it generates a new
state in the application (in case of a Web-Application or a RESTful
architecture) ?


3) If the command is persisted, does that mean we deal with Event-Sourcing
(by construct when we use CQRS) ? Does Event-Sourcing invalidate the
database update process ? (as if state is reconstructed from the
Event-Store, maintaining the database seems useless) ?


*Does CQRS only apply to multi-databases systems (when data is propagated
on separate databases), and, if it deals with memory-transient models, does
that fit well with Web-Applications or RESTful services ?*


Thanks,


Rénald