Information Science 1

Program  Development

-­‐Algorithms  and  Problem  Solving-­‐      

College of Information Science and Engineering Ritsumeikan University

Week  06  

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Topics covered l  Terms and concepts from Week 05 l  The software development process

– software – software life cycle – life-cycle models

l  Software design - algorithm - design (and development) formal tools

l  Quiz

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Recall Week 05 l  Signed, unsigned l  Positive, negative l  Real numbers, floating point numbers l  Signed magnitude, sign-magnitude l  Two’s complement (2’s complement) l  Invert, flip, 1’s complement l  Duplicate, sign extension l  Range, out of range, overflow l  IEEE 754 (“I triple E 754”) l  Exponent, fraction, infinity, NaN

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Our goals today l  To understand the software

development process

l  To introduce the concept of the software product life cycle and software process models

l  To learn what an algorithm is

l  To survey popular formal tools used in program design and development

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The concept of software product

l  A specific set of computer programs and associated documentation (such as user requirements, design models, user manuals, etc) are called a software product

l  A software product may be developed for a particular customer – custom software – or for a general market – generic software

l  A new software product can be created by developing new programs, configuring generic software systems, or reusing existing software

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The software development process

l  The software development process is a set of activities having their goal as the development or evolution of software. It always includes: - Specification: What the system should do and

its development constraints - Development: Production of the software

system - Validation: Checking that the developed

software is what the customer wants - Evolution: Changing the software in response

to changing demands

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Software life cycle l  All the processes of software development

and use are called the software processes. The software life cycle is an ordered set of software processes

l  Fundamental assumptions of software product development: - Good software processes lead to good

products - Good software processes reduce risk

l  Software process models are simplified representations of the software life cycle, presented from a specific perspective

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Software life cycle: A simplified view

Requirements

Operation and

Maintenance Implementation

Design

Feasibility study and Planning

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The Waterfall model

Requirements Analysis

System design

Unit Testing & Integration

System Testing

Operation & Maintenance

Program design

Coding

Acceptance Testing Software processes

Assumed order

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Requirements analysis l  This phase of the software life cycle is to

establish system's services, constraints, and goals through interaction with system prospective users (i.e. the client)

l  The requirements analysis phase is usually comprised of activities related to:

- Feasibility study (which is often carried out separately from other activities)

- Requirements elicitation (i.e. understanding and analysis of what the client needs)

- Requirements definition - Requirements specification

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System and Program design l  The system design phase is to establish an

overall system architecture, and to partition all the requirements into hardware requirements and software requirements

l  During the program design phase, the previously established system functions are represented in a form that can unambiguously be understood and can be transformed into one or more executable programs

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Coding and Unit testing l  Through coding (or, in other words,

programming), the software design is realized as a set of programs or program units. These programs can be written specifically, acquired from elsewhere, or obtained by modifying programs developed previously

l  Individual programs and subsystems are tested against specifications during the unit testing phase

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Integration, System testing, and Acceptance testing

l  Integration and system testing are usually concurrent activities that include: -  Integration of individual programs into larger

modules (subsystems) and, ultimately, into a complete system

- Testing the subsystems and, then, the whole system against the specified requirements

- Delivering the system to the client l  During acceptance testing, the client

performs independent testing before accepting the system and putting it into operation

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Operation and Maintenance l  This phase of the software life cycle

includes activities related to — System operation: The product is put

into practical use — System maintenance: Errors/“bugs” and

other problems are identified and fixed — System evolution: The product evolves

over time as requirements change, to add new functions or adapt to the technical environment

— Phasing out of the software product: The system is withdrawn from service

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Feedback and the Waterfall model Requirements Analysis

System design

Unit & Integration Testing

System Testing

Operation & Maintenance

Program design

Coding

Acceptance Testing

Each phase may need to be iteratively refined due to new understanding emerging at later stages

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System documentation l  Each (sub)system’s documentation

describes the purpose of the processing system, and it usually includes: — Computer system flowcharts — Input and output descriptions — File descriptions — Error messages

l  System documentation also assigns responsibility for performing each control and processing procedure, as well as error-correction procedures

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The concept of algorithm l  Definition:

An algorithm is a finite set of unambiguous, executable instructions that direct a terminating activity

l  In an algorithm, always — the number of steps (instructions) is

finite — we are able to do each of the

instructions — when we have followed all of the steps,

we obtain a solution, and then stop

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Designing Algorithms: A Methodology

1.  Read the problem and establish the input and the output

2.  Identify, what variables are needed? 3.  Figure out, what computations are required to

achieve the output? l  Usually, first steps in your algorithm are to

bring input values to the variables l  Usually, last steps are to display the output l  So, the middle steps are to do the

computation l  If processes are to be repeated, add loops

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Algorithm design tools: Flowchart

l  A flowchart is a logic diagram used to describe each step that the program must perform to arrive at the solution

l  It is a very popular design tool used for showing an algorithm in a graphical form. Most common flowchart symbols are:

Direction of logic flow

Beginning or end of a task

Input/output operation

Logic comparison operation. Always has one entry and two exit points

Data manipulation operations e.g arithmetic

Logic flow connectors

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Flowchart: Example l  Suppose you want to calculate the

squares of the integers from 2 to 7 – a simple solution would be to arrange a loop

for both calculation and display

is i > 7 ? i = 2

i = i + 1

NO

YES

Display i 2 Start

Stop

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5 purposes of flowcharting 1. An aid in developing the logic of a

program 2. Verification that all possible conditions

have been considered in a program 3. Provides a means of communicating

with others about algorithms (especially good for international communication)

4. A guide in coding the program 5. Documentation for the program

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Algorithm design tools: Pseudocode

l  Pseudocode is a textual description of a program l  Basic pseudocode operations:

— Read the input from user — Print/Display the output to the user — Carry out basic arithmetical computations — Conditional operations: Execute an operation if

the condition is true — Repeat operations: Execute a block operation

multiple times until a certain condition is met l  Pseudocode is a simplified form of English (or any

other natural language – Japanese, Vietnamese, Arabic, etc), but looks like programming

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Algorithm design tools: Hierarchy chart

l  Hierarchy chart is a graphical description of how parts of a (sub)system are connected

l  A hierarchy chart: — Shows the overall system structure — Describes what each part, or module, of the

system does — Also shows how each module relates to other

modules in the system l  There are two hierarchy chart symbols: rectangles

(to indicate the parts) and lines (to connect related modules). Arrows may also be used to show the flow

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Algorithm design tools: UML l  The Unified Modeling Language (UML) is a

language for – visualizing, – specifying, – constructing, and – documenting an information system

l  UML is not “just for” software development, and it can be used “outside” the domain of computer (information) science

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UML “things”

Structural Things 1. Class

2. Interface

3. Colla- boration

4. Use case

5. Active class

6. Components

7. Nodes

Behavioral Things

2. State mecha- nism

1. Interaction

Grouping Things 1. Packages

Annotational Things 1. Notes

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UML diagrams l  A UML diagram is a graphical presentation of a

set of elements, most often in the form of a connected graph of things and relationships. UML includes 9 diagrams:

1. Class (and Object) Diagrams 2. Use Case Diagrams 3. Collaboration Diagrams 4. Sequence Diagrams 5. Package Diagrams 6. Component Diagrams 7. Deployment Diagrams 8. Activity Diagrams, and 9. State Diagrams

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UML: Example (a class diagram)

DVD Movie VHS Movie Video Game

Rental Item {abstract}

Rental Invoice

1..* 1

Customer

Checkout Screen

0..1

1

Simple Association

Class

Abstract Class

Simple Aggregation

Generalization

Composition (Dependency)

Multiplicity

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What you are supposed to know after this class

l The phases of the software life cycle (as in the Waterfall model)

l Algorithm definition l Software design tools: flowchart

and pseudocode l You are also advised to learn

hierarchy charts and, especially, (in the future) the UML

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Homework

l Read these slides l Do the self-preparation work l Learn the vocabulary l Consult, whenever necessary, the

textbook materials

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Next class

l  Overview and mid-semester evaluation for the first six weeks: from Week 01 to Week 06

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Quiz 03