There is such a piece of SVN magic (they call it externals), but ideally you don't want to use it, as it's not quite seamless -- you can't commit to both the master and linked repositories with a single "svn commit", so it isn't atomic.

The right way to do this IMO is have a single repository containing the backend and all the frontends. That way, tags and commits are atomic across the whole thing. If the different frontends have different release schedules or whatever, you could always just branch each one's subdirectory. (Or not -- svn lets you do such a thing, but I've always preferred to branch the whole lot for simplicity's sake.)


Peter