Programming Layer
Lecture 8
Layers of Computing Systems
Communications
Applications
Operating Systems
Programming
Hardware
Information
Programming Layer
Top down design
Object oriented
design
Programming
Procedural
programming
Low level
programming
OOP
High level
programming
Problem Solving
• The act of finding a solution to a perplexing
question
• A computer is not intelligent
– Computer can do nothing without being told what to
do.
– cannot analyze a problem and come up with a
solution.
– Human (the programmer) must analyze the problem,
develop the instructions for solving the problem (the
program), and then have the computer carry out the
instructions.
HOW TO SOLVE IT by G. Polya
1. You have to understand the problem.
2. Find the connection between the data and the
unknown.
– You may be obliged to consider auxiliary problems if
an immediate connection cannot be found.
– You should obtain eventually a plan of the solution
(algorithm).
3. Carry out your plan
– test the solution to see if it works
4. Examine the solution obtained
– for future re-use
Problem solving strategies
heuristics
• Look for Familiar Things
– never reinvent the wheel. If a solution exists, use
it. If you’ve solved the same or a similar problem
before, just repeat the successful solution.
• Divide and Conquer
– break up a large problem into smaller pieces that
we can solve individually.
Algorithm
• Algorithm – unambiguous instructions for
solving a problem or subproblem in a finite
amount of time using a finite amount of data
Pseudocode – presenting algorithm
• Pseudocode - uses a mixture of English and
formatting to make the steps in the solution
explicit. Used to present the algorithm
The computer problem-solving process
The interaction between
problem-solving phases
PROBLEM SOLVING
METHODOLOGIES
Problem solving methodologies
• top-down design (also called functional
decomposition)
– A technique for developing a program in which the
problem is divided into more easily handled subproblems,
the solutions of which create a solution to the overall
problem
• object-oriented design (OOD).
– Data and the algorithms that manipulate the data are
bundled together in the object-oriented view, thus making
each object responsible for its own manipulation
(behavior).
– Underlying object-oriented design (OOD) are the concepts
of classes and objects.
Problem solving methodologies
TOP-DOWN DESIGN
Top-down design
• Create hierarchical structure, also known as a
tree structure, of problems and subproblems,
called modules.
– Module - a self-contained collection of steps that
solves a problem or subproblem
• Modules at one level can call on the services
of modules at a lower level.
– These modules are the basic building blocks of an
algorithm.
An example of top-down design
Worked example:
Subdividing the party planning
Example: computer example
• Problem: Create an address list that includes
each person’s name, address, telephone
number, and e-mail address.
– This list should then be printed in alphabetical
order.
– The names to be included in the list are on scraps
of paper and business cards.
Summary of top-down methodology
1.
2.
3.
4.
Analyze the Problem
Write the Main Module
Write the Remaining Modules
Re-Sequence and Revise as Necessary
Problem solving methodologies
OBJECT-ORIENTED DESIGN (OOD)
Object-oriented design
• Object-oriented design is a problem-solving
methodology that produces a solution to a
problem in terms of self-contained entities
called objects, which are composed of both
data and operations that manipulate the data.
– Object-oriented design focuses on the objects and
their interactions within a problem.
Object Orientation
• Object - An entity or thing that is relevant in
the context of a problem
• Object class or class - A description of a group
of objects with similar properties and
behaviors
• Fields - Named items in a class; can be data or
subprograms
• Method - A named algorithm that defines one
aspect of the behavior of a class
Relationships between Classes
• Containment - A mechanism whereby one
class contains an object of another class as a
field
• Inheritance - A mechanism by which one class
acquires the properties - data fields and
methods - of another class
Object-Oriented Design Methodology
• Brainstorming and Filtering
– Determining the possible classes in the problem and filter the ones that can be combined
or identify missing ones
– Record the resulting set in CRC cards
CRC - Class-responsibility-collaboration card
• Scenarios
– is the stage in which the behavior of each class is determined.
– assign responsibilities to each class - the tasks that each class must perform.
Responsibilities are eventually implemented as subprograms.
• what a class must know about itself (knowledge) and what a class must be able to do (behavior).
• A class encapsulates its data (knowledge) - objects in one class cannot directly access data in
another class.
• Responsibility Algorithms
– algorithms must be written for the responsibilities.
– Because of the process of focusing on data rather than actions in the object oriented view
of design, the algorithms for carrying out responsibilities tend to be fairly short.
• Knowledge responsibilities usually just return the contents of one of an object’s variables, or
send a message to another object to retrieve it.
• Action responsibilities are a little more complicated, often involving calculations
Example: problem definition
• Problem: Create an address list that includes
each person’s name, address, telephone
number, and e-mail address. This list should
then be printed in alphabetical order. The
names to be included in the list are on scraps
of paper and business cards.
Example: Brainstorming and Filtering
• What are the possible objects?
– There must be the host or hostess, the guests, the
menu, and the food.
• Where is the party going to be?
– We need an address object.
• Are the invitations to be done by phone or by
invitation?
– Let’s assume by written invitation, so we have
invitation objects.
Example: Brainstorming and Filtering
Example: Brainstorming and Filtering
Initial list
Filtered list
address list
name
address
phone number
email
list
order
names
list
paper
Craps
cards
address list
name
address
telephone
email
Record data to CRC cards
Responsibility algorithms
• Person class - There are two responsibilities to
be decomposed: initialize and print.
– Because each of the fields of the class is a class,
we can just let each initialize and print itself.
Responsibility algorithms
• Name class This class has the same two
responsibilities: initialize and print; however, the
algorithms are different.
– For Initialize, the user must be prompted to enter the
name and the algorithm must read the name.
– For Print, the first and last names must be output with
appropriate labels.
Responsibility algorithms
• Address, Telephone, and E-mail classes
– The algorithms for the responsibilities for these
classes are mirror images of the algorithms for
class Name.
Important topics in OOD
• Information hiding The practice of hiding the details of a
module with the goal of controlling access to the details of
the module
• Abstraction A model of a complex system that includes
only the details essential to the viewer
– Data abstraction - The separation of the logical view of data
from its implementation
– Procedural abstraction - The separation of the logical view of an
action from its implementation
– Control abstraction - The separation of the logical view of a
control structure from its implementation
– Control structure - A statement used to alter the normally
sequential flow of control
Programming languages
• Programming language - A set of rules, symbols,
and special words used to construct a program that is, to express a sequence of instructions for a
computer
• Program - A sequence of instructions written to
perform a specified task
• Syntax - The formal rules governing the
construction of valid instructions
• Semantics - The set of rules that gives the
meaning of instructions in a language
Homework
• Computer Science Illuminated, Chapter 6, end
of the book exercises