Under what conditions would one favor apps talking via a message queue instead of via web services (I just mean XML or JSON or YAML or whatever over HTTP here, not any particular type)?
I have to talk between two apps on a local network. One will be a web app and have to request commands on another app (running on different hardware). The requests are things like creating users, moving files around, and creating directories. Under what conditions would I prefer XML Web Services (or straight TCP or something) to using a Message queue?
The web app is Ruby on Rails, but I think the question is broader than that.
