The ADT model is shown in Figure 2. The dark shaded area with an irregular outline represents the model. Inside the abstract area are two different aspects of the model: the data structure and the operational functions. Both are entirely contained in the model and are not within the user’s scope. However, the data structure is available to all of the ADT’s operations as needed, and an operation may call on other functions to accomplish its task. In other words, the data structure and the functions are within scope of each other.