It depends entirely on what kind of system you're building. A common system design is to have a database, a RESTful API, and then a bunch of clients which inte

It depends entirely on what kind of system you're building. A common system design is to have a database, a RESTful API, and then a bunch of clients which interact with the API in order to do whatever they need to do. The method of integration between the different parts of your system are up to you, but having an API to manage the ultimate state of your system is easy to think about and pretty simple to implement too. Without knowing more about what kind of system you're trying to build, it's difficult to give you any more concrete advice. Different components will require different things.