对Google App Engine和Google Cloud Endpoints感到困惑

I am building my mobile apps (Android and iOS). I am not sure if I understand this correctly, but it seems Cloud Endpoints allow you to develop and deploy your own APIs, while App Engine assists you in building a server application? It seems App Engine also allows you to build a web application backend that exposes REST service APIs? So it can do whatever Cloud Endpoints can do? If I use Cloud Endpoints, can my APIs interact with some kind of DB? Is there anything I can do in App Engine but cannot do in Cloud Endpoints in the context of building a REST backend for mobile apps?I am building my mobile apps (Android and iOS).