You should probably read the first few chapters of the svn book at svnbook.red-bean.com/nightly/en/svn-book.html especially the first chapter.
But very simple answers to your question would be:
> Is there a WebService interface to svn?
WebDav not web service.
> How complex is to develop to direct over http?
http is one of the commonly used protocols an svn client uses to talk to an svn server.
> Is there any "http" simple "bridge" between a generic development
> system an svn?
I don't know what this means.
BOb