Minimalist docker-compose file

I have a number of directories each with a Dockerfile. I am able to build each one independently. I want to be able to use docker-compose to bring them up. The only thing I need to specify in the compose is the links and volumes. Any snippets of a simple compose example I can use? All the examples I'm seeing are referring to the images etc and those are already specified in the individual Dockerfiles. Will be nice to see a few examples.

docker-compose.yml |___a |___b |___c