Introduction to Data Abstraction

Data Structures and File
Organization
Dennis B. Gajo, MIT
Professor,
University of Mindanao
dennis.gajo@gmail.com

Learning Objectives
 Compare and contrast the various
levels of data types
 Understand the concept of abstraction
 Distinguish the different forms of data
types
 Appreciate the benefits of abstraction
through abstract data types

Intro to data structures and
abstract data types
 What is abstraction?
 What are the attributes of a variable?
 What is an abstract data type (ADT)?
 The forms of data types
 The levels of data types
 Benefits of data abstraction through
ADTs

abstract data types
 Abstraction
 The ability to view something as a high-level
object while temporarily ignoring the enormous
amount of underlying detail associated with that
object
 Viewing something only in terms of its external
appearance, without regard to its internal
implementation
 It gives attention to the WHAT rather than the
HOW
 Example :
 Organization, body organ, any object, a program

abstract data types
 Procedural Abstraction
 Function declaration
 int addintegers(int a, int b);
 Use addintegers() to add integers a and b
and return the sum.
 Function call
 int x = addintegers(5,6);
 We don’t really care what happens inside the
function body. What we what to know is what
the function does and how to use it.

abstract data types
 Benefits of abstraction
 Helps us understand complex systems
 Makes things easy to absorb and
manipulate

abstract data types
 Abstraction to data structuring
 Seven attributes
 Name
 Address
 Value
 Lifetime
 Scope
 Type
 Size

abstract data types
 Name
 A textual label used to refer to that variable/data
in the text of the program
 Address
 Denotes its location in memory
 Value
 Quantity which that variable represents
 Lifetime
 Interval of time during the execution of the
program in which the variable is said to exist

abstract data types
 Scope
 Set of statements in the text of the source
program in which the variable is said to be
visible
 Type
 The set of values which can be assigned to the
value attribute and the set of operations which
can be performed on the variable
 Size
 The amount of storage required to represent the
variable

abstract data types
 Variable : int x;
 Name x
 Address memory location
 Value assigned or input
 Lifetime run-time
 Scope block of code
 Type int
 Size 2 bytes

abstract data types
 Data type hierarchy – three levels
 Hardware data types
 Directly supported by the hardware
 Integers, float, characters
 Virtual data types
 Do not actually exist in the sense of being
directly represented by the hardware
 The compiler creates these data types
 Arrays, structures, sets, and pointers

abstract data types
 Abstract data types (ADTs)
 Created by programmers to solve a given
problem: user-defined
 Defined only in terms of the operations
that may be performed on them
 Frees programmers from the limits
imposed by a given programming
language regardless of how interesting or
powerful that language might be

abstract data types
 ADT specifications : four factors
 Domain of values
 Data type of components
 Structural relationship between
components
 Operations on the ADT

ADT Specification
 Domain of values
 Set of values that may be assigned to
variables of this type
 Forms of data type
 Atomic / Simple
 Domain of values is made up of non-
decomposable or primitive elements
 Composite / Structured
 Values can be further divided into elements
called components
 Also called data structure

ADT Specification
 Data Structure
 An aggregation of atomic and composite data
types into a set with defined relationships.
 In other words, a data structure is:
 A combination of elements each of which is either a
data type or another data structure
 A set of associations or relationships (structure)
involving the combined elements.

ADT Specification
 Data type of components (structured)
 What types of data this ADT will contain?
 All integers? All floats? All characters? Mixed?
 Structural relationship of the components
(structured)
 What type of structural relationship should the
components have?
 Should the first element be accessed last? Should
the last element be accessed first? Should an
element be connected to the other elements?

ADT Specification
 Operations on the ADT
 What are the things that the ADT can do?
 This is the most important step in the ADT design
process.
 The operations are the only ones we will be able to
use.
 A data structure must be complete – that is, the
design must include all operations needed to utilize
fully the capabilities of the ADT.

Properties of an ADT
 Data encapsulation
 A process of packaging together a collection of
data values together with the operations on those
values.
 Sample – integer
 Values (-maxint to +maxint)
 Operations (+, -, *, /)
 Information hiding
 Masking the internal implementation of the ADT
so that users do not have to know the messy /
gory details of the ADT specification.
 ONLY the OPERATIONS are accessible to the
user.

Benefits of data abstraction
through ADTs
 Security and software integrity
 Programmer controls access to all resources,
guaranteeing that no improper, illegal, or
potentially dangerous operations can be carried
out
 Maintainability
 External module is independent of the
underlying implementation
 Flexible
 Cost-effective

Benefits of data abstraction
through ADTs
 Sharing and reusability of software
 Easy to import through data
encapsulation
 Code sharing improves productivity
 Cost-effective
 Intellectual manageability
 Simplify things
 Focus on the bigger picture

Introduction to Data Abstraction

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