The most serious applications need to persist certain amounts of data. This data could be transactional data, user preferences, or the current state of the application. There are many ways in which data can be persisted in our applications. Determining the appropriate way to persist this data can be one of the most critical decisions that an architect needs to make.

As an architect, we should separate the actual data storage from the business logic. This will allow the application to change how the data is persisted in the future without having to change the business logic. This separation creates what is called a data access layer.

When designing an application, it is important to design a good data access layer because having a good data access layer will make the code much easier to maintain as the requirements change. If we separate the data-access layer...