Is it possible to use the Google App Engine with datastore only and keep your application on an external traditional server?
I'm interested in the GAE for Business SQL service coming soon but I only want to use GAE for the database. I would like to keep the php application on a traditional server for a variety of reasons.
Is this possible?
Yes it is possible and GAE is fairly used in this specific scenario; think about the hundreds of Iphone/Android applications that use GAE as back-end.
A simple common design would have:
A Web API to communicate with GAE datastore since you can't connect directly to it from your php application. Have a look to restlet for a cool RESTful Java web framework that supports GAE or the new Appengine-rest-server Python project .