BUS611: Data Management

As we consider the wide set of things in the world that we would like to represent in our programs, we find that most of them have compound structure. For example, a geographic position has latitude and longitude coordinates. To represent positions, we would like our programming language to have the capacity to couple together a latitude and longitude to form a pair, a compound data value that our programs can manipulate as a single conceptual unit, but which also has two parts that can be considered individually.

The use of compound data enables us to increase the modularity of our programs. If we can manipulate geographic positions as whole values, then we can shield parts of our program that compute using positions from the details of how those positions are represented. The general technique of isolating the parts of a program that deal with how data are represented from the parts that deal with how data are manipulated is a powerful design methodology called data abstraction. Data abstraction makes programs much easier to design, maintain, and modify.

Data abstraction is similar in character to functional abstraction. When we create a functional abstraction, the details of how a function is implemented can be suppressed, and the particular function itself can be replaced by any other function with the same overall behavior. In other words, we can make an abstraction that separates the way the function is used from the details of how the function is implemented. Analogously, data abstraction isolates how a compound data value is used from the details of how it is constructed.

The basic idea of data abstraction is to structure programs so that they operate on abstract data. That is, our programs should use data in such a way as to make as few assumptions about the data as possible. At the same time, a concrete data representation is defined as an independent part of the program.

These two parts of a program, the part that operates on abstract data and the part that defines a concrete representation, are connected by a small set of functions that implement abstract data in terms of the concrete representation. To illustrate this technique, we will consider how to design a set of functions for manipulating rational numbers.

Source: John DeNero, https://composingprograms.com/pages/22-data-abstraction.html
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