Separating code into independent entities

Before we start with the implementation, we will separate our code into independent entities. Each entity will cover a single responsibility and therefore will be implemented when we cover a certain Spring functionality.

We will start with the main classes that will represent the data we will actually handle: Notes and TODOs. Then we will describe user-related stuff: the users themselves and the roles we plan to assign to them. Later, when we actually implement most of them, we will introduce some new entities to cover additional responsibilities. This will be explained in Chapter 3, Building Your First Spring RESTful Service with Kotlin.