MODULE 5 PROGRAM DESIGN AND SPECIFICATION Overview INTRODUCTION

MODULE 5 - PROGRAM DESIGN AND SPECIFICATION - Overview • INTRODUCTION In this session we consider the important issue of program design – the third stage in the Program Development Framework. The basic knowledge of program design needed to write programs of reasonable quality will be discussed. Mr. Joseph Ecklu (DCS) Slide 1

Session Objectives After studying the session the student should be able to - Use the results of the analysis stage i. e. program specification to do design - Know the aims of the design stage - Ensure program specification and its correctness - Describe the program development stages - Explain the concepts that lie behind program design - List the tools required for good design Mr. Joseph Ecklu (DCS) Slide 2

Reading List • REFERENCES 1. C. S. FRENCH, COMPUTER SCIENCE (2000) chpt 18 2. Eric Grimson and John Guttag, 6. 00 Introduction to Computer Science and Programming, Fall 2008. (Massachusetts Institute of Technology: MIT Open. Course. Ware). http: //ocw. mit. edu (accessed 01 28, 2015). License: Creative Commons Attribution. Noncommercial-Share Alike. 3. Jesse Dunietz, Geza Kovacs, and John Marrero. 6. 096 Introduction to C++, January IAP 2011. (Massachusetts Institute of Technology: MIT Open. Course. Ware), http: //ocw. mit. edu (Accessed 28 Jan, 2015). License: Creative Commons BY-NC-SA Mr. Joseph Ecklu (DCS) Slide 3

PROGRAM DESIGN AND SPECIFICATION • Goals Mr. Joseph Ecklu (DCS) Slide 4

PROGRAM DESIGN AND SPECIFICATION TOPICS The importance of good programming methods Program Design Program specification and correctness Methods for program development Program Development Framework/ Stages in programming • Program Design Concepts • • • Mr. Joseph Ecklu (DCS) Slide 5

PROGRAM DESIGN AND SPECIFICATION Mr. Joseph Ecklu (DCS) Slide 6

Good Programming Methods • Importance of Good Programming Methods Reasons that greater efforts should be put into program design include the following : 1. Great reliance placed upon computers for all applications – military, banking, health 2. High cost of programming labour 3. Need for good-quality programming is greater than ever Mr. Joseph Ecklu (DCS) Slide 7

PROGRAM DESIGN AND SPECIFICATION Mr. Joseph Ecklu (DCS) Slide 8

PROGRAM DESIGN AND SPECIFICATION • Aims of Program Design – Reliability : the program can be depended upon always to do what it is supposed to do – Maintainability: the program will be easy to change or modify when the need arises – Portability: the program will be transferable to a different computer with a minimum of modification – Readability: the program will be easy for a programmer to read and understand – Performance: the program causes the tasks to be done quickly and efficiently – Storage Saving: the program is not allowed to be unnecessarily long Mr. Joseph Ecklu (DCS) Slide 9

Mr. Joseph Ecklu (DCS) Slide 10

Program specification and correctness • Program specification gives a specification of what the proposed program is required to do • A program that meets its specification is said to be ‘correct’ • Where the specification is wrong, this could lead to program being ‘correct’ but ‘unsuitable’ • The specification may be right, it may be very difficult to ensure that the program is correct Mr. Joseph Ecklu (DCS) Slide 11

Program specification and correctness • Good programming Methods are required to ensure that the programmer – produces correct programs from specifications that truly express the requirements – Correct programs must be • • • Mr. Joseph Ecklu (DCS) Reliable Maintainable Portable Readable efficient Slide 12

Methods for Program Development • Program Development Framework Stages: 1. Problem Definition: as defined by System Specification 2. Analysis : Understanding the problem , defining the method of solution 3. Design : developing the methods using suitable aids 4. Coding : typing the instructions into the computer using a programming language 5. Testing and debugging: testing the program and removing errors 6. Documentation: writing all the work involved in producing the program Mr. Joseph Ecklu (DCS) Slide 13

Program Development Framework Analysis Mr. Joseph Ecklu (DCS) Slide 14

Program Development Framework • Analysis The programmer need to know exactly - what the program is required to do and normally works from a program specification - The program specification is normally part of a System Specification - The System Specification defines the whole system of which the program may be a small part Mr. Joseph Ecklu (DCS) Slide 15

Program Development Framework • Analysis The program specification must be well defined - Input specification - Process specification - Output specification - Limitations of the program - A good specification will specify what processing is needed by giving the exact relationship between outputs and the inputs from which they are derived Mr. Joseph Ecklu (DCS) Slide 16

Program Development Framework • Analysis - A good specification will specify - what processing is needed by giving the exact relationship between outputs and the inputs from which they are derived - Rather than prescribing how the program should be written Mr. Joseph Ecklu (DCS) Slide 17

Program Development Framework • Analysis - Plan the method of solution - Determine the extent of the task - For large programs share the programming effort among many programmers - Modules/segments are the separate parts - Modules are prepared and tested separately - Integration : Modules are linked together and tested as a whole Mr. Joseph Ecklu (DCS) Slide 18

Program Development Framework • Design Tools for design include the following - Top-down design - Algorithms - Flowchart - Pseudo-codes (details later ) Mr. Joseph Ecklu (DCS) Slide 19

Program Development Framework • Coding The last step in Top-down design - The instructions written in pseudo-codes or flowcharts are written in a programming language - There are different types of programming languages as discussed under classification of programming languages - In this course, imperative / structured/ procedural language will be used - C++ is the language for practising the programming concepts Mr. Joseph Ecklu (DCS) Slide 20

Program Development Framework • Testing and debugging the Programs once written / coded has to be - Tested: checked that it has been written out and transcribed correctly - that it does what it is suppose to do i. e. correct - debugged: tests may reveal errors which have to be corrected Mr. Joseph Ecklu (DCS) Slide 21

Program Development Framework • Testing and debugging the Program Stages of testing - Unit testing: testing the separate components - Integration testing: testing the separate components as they are put together - System testing: testing the whole program once it is in its final form in which it will be used - User acceptance testing: the user of the program (possibly the customer) testing the program to see that it is what is required Mr. Joseph Ecklu (DCS) Slide 22

Program Development Framework • Documentation Very important that the work of the programmer in producing a finished program is fully documented Documents include - Statement of the problem/system specification - Pseudo-codes - Codes - Test data and results Mr. Joseph Ecklu (DCS) Slide 23

Program Development Framework • Documentation Note: - Producing these documents should be done as part of each stage in programming and not as an afterthought - Good documentation aids maintenance of the program during its lifetime Mr. Joseph Ecklu (DCS) Slide 24

PROGRAM DESIGN CONCEPTS • Concepts relevant to the general problems of Program Design - Computability - Complexity - Correctness Mr. Joseph Ecklu (DCS) Slide 25

PROGRAM DESIGN CONCEPTS • Computability In programming our concern is - What tasks computers can do and how they do them - Undesirables : There are problems that computers can not solve e. g. Tasks that for practical reasons , tasks that can be proven to be theoretically impossible, ‘the halting problem’ - Computable : tasks that in principle can be performed by a machine Mr. Joseph Ecklu (DCS) Slide 26

PROGRAM DESIGN CONCEPTS • Complexity In programming complexity is measured in terms of the quantity of resources used - Time : taken to perform the task - storage : requirements Algorithm : for many tasks there may exist many alternative algorithms and for practical reasons a knowledge of their complexity will help us make the best choice Mr. Joseph Ecklu (DCS) Slide 27

PROGRAM DESIGN CONCEPTS • Correctness A program is correct if it meets its specification To prove that a program is correct - Show that for all permissible input to the program will produce the required results Mr. Joseph Ecklu (DCS) Slide 28

PROGRAM DESIGN CONCEPTS • Correctness Test data A set of carefully selected data used in testing the program Testing may be done - By executing the program on the computer - ‘dry run’ = simulating program execution by a manual pencil and paper exercise Mr. Joseph Ecklu (DCS) Slide 29

PROGRAM DESIGN CONCEPTS • Correctness 2 basic types of testing - Functional Testing - Logical testing Mr. Joseph Ecklu (DCS) Slide 30

PROGRAM DESIGN CONCEPTS • Functional / blackbox testing - Based upon typical, extreme and invalid data values that are representative of those covered by the specification - Used at the final stage of programming as a basis for accepting or rejecting the program - Not adequate by itself, logical testing by the programmer during program development tends to be more beneficial Mr. Joseph Ecklu (DCS) Slide 31

PROGRAM DESIGN CONCEPTS • Logical testing / white box - Based upon examining the internal structure of the program and selecting data which give rise to the alternative cases of control flow e. g. both paths through an if…then…else Mr. Joseph Ecklu (DCS) Slide 32

PROGRAM DESIGN CONCEPTS • bug A program fault that causes a program to fail during testing, or after it has been commissioned • Debugging The process of finding and getting rid of bugs Mr. Joseph Ecklu (DCS) Slide 33

PROGRAM DESIGN CONCEPTS • Trouble shooting bugs - Bugs are often the result of poor workmanship on the part of - Persons who produced the program specification or - Persons who wrote the program - Reasons for the occurrence of bugs must be investigated fully and that - Program’s design and implementation reworked where necessary Mr. Joseph Ecklu (DCS) Slide 34 are

PROGRAM DESIGN CONCEPTS • Correctness A program is correct if it meets its specification Mr. Joseph Ecklu (DCS) Slide 35

Session Summary It is importance the go through a systematic approach in designing a program to yield the desired functionality of the program. This stages for program design and specifications are - Analysis - Design - Coding - Testing and debugging - Documentations Mr. Joseph Ecklu (DCS) Slide 36

Trial Question 1. 2. 3. 4. 5. List and explain the various stages of testing What is the importance of documentation List in order the stages of program development Explain briefly each stage specified in 2. above What are the importance of good programming methods Mr. Joseph Ecklu (DCS) Slide 37