The original architecture included conceptual layer

Layers of Data Abstraction

Databases have the unique capability of presenting multiple users of the data with their own distinct views of that data while storing the underlying data only once. These are collectively called user views. A user in this context is any person or appli-cation that signs on to the database for the purpose of storing and/or retrieving data. An application is a set of computer programs designed to solve a particular business problem, such as an order-entry system, a payroll-processing system, or an account-ing system.

Figure 1-1 Database layers of abstraction