Data Abstraction Defined

This is the second of a 4 part series, for those of you new to object-oriented programming, discussing the 4 major principles of an object-oriented language: Data Abstraction, Encapsulation we’ve already discussed, Polymorphism and Inheritence. Data abstraction is the simplest of principles to understand. Data abstraction and encapuslation are closely tied together, because a simple definition of data abstraction is the development of classes, objects, types in terms of their interfaces and functionality, instead of their implementation details. Abstraction denotes a model, a view, or some other focused representation for an actual item. Its the development of a software object to represent an object we can find in the real world. Encapsulation hides the details of that implementation.

Abstraction is used to manage complexity. Software developers use abstraction to decompose complex systems into smaller components. As development progresss, programmers know the functionality they can expect from as yet undeveloped subsystems. Thus, programmers are not burdened by considering the waysin which the implementation of later subsystesm will affect the design of earlier development.

The best definition of abstraction I’ve ever read is: “An abstraction denotes the essential characteristics of an object that distinguish it from all other kinds of object and thus provide crisply defined conceptual boundaries, relative to the perspective of the viewer.” — G. Booch, Object-Oriented Design With Applications, Benjamin/Cummings, Menlo Park, California, 1991.

Lets look at this code for a person object. What are some things that a person can do? Those things must be represented here in our software model of a person. Things such as how tall the person is, and the age of the person; we need to be able to see those. We need the ability for the person to do things, such as run. We need to be able to ask the person if they can read.

Public Class Person

    Private _height As Int16

    Public Property Height() As Int16

        Get

            Return _height

        End Get

        Set(ByVal Value As Int16)

            _height = Value

        End Set

    End Property
    Private _weight As Int16

    Public Property Weight() As Int16

        Get

            Return _weight

        End Get

        Set(ByVal Value As Int16)

            _weight = Value

        End Set

    End Property
    Private _age As Int16

    Public Property Age() As Int16

        Get

            Return _age

        End Get

        Set(ByVal Value As Int16)

            _age = Value

        End Set

    End Property
    Public Sub Sit()

        ‘ Code that makes the person sit

    End Sub
    Public Sub Run()

        ‘ Code that makes the person run

    End Sub
    Public Sub Cry()

        ‘ Code that make the person cry

    End Sub
    Public Function CanRead() As Boolean

        ‘ Code that determines if the person can read 


        ‘ and returns a true or false

    End Function
End Class