Software Engineering CH1 Slides

8/20/2019 Software Engineering CH1 Slides

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Chapter 1. Introduction

Some slides are adopted from Kung D., “Object-Oriented Software Engineering: An Agile Unified Methodology”


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Key Takeaway Points

• Software engineering aims to significantly improvesoftware productivity and software quality whilereducing software costs and time to market.

• Software engineering consists of three tracks ofinteracting life cycle activities:

– software development process

– software quality assurance, and – software project management

• Object-oriented (OO) software engineering is a

specialization of software engineering. It views theworld and systems as consisting of objects thatinteract with each other.


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What Is Software Engineering?

Software engineering as a discipline is focused

on

• research, education, and application of engineering processes and methods

• to significantly increase software productivity (P)

and software quality (Q) while reducing softwarecosts (C) and time to market (T) – software PQCT.

• What is the focus of data base systems?

• What is the focus of operating systems?


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Why Software Engineering?

1. Software is expanding into all sectors of oursociety:

• Companies rely on software to run and expand their

businesses.• Software systems are getting larger and more complex – millions of lines of code.

• Software costs are 90 – 95% of total system costs(software costs were only 5 – 10% of total system coststwo decades ago.)

• Embedded systems contain application specificintegrated circuits (ASIC), which are costly to replace – software quality is critical.

We need an engineering approach to softwaredevelopment.


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2. Large software systems development requiresteamwork and software engineering supportsteamwork.

• A typical software engineer produces an average 50–100lines of source code per day.

• A small system of 10,000 lines of code requires onesoftware engineer to work between 100 and 200 days or 5to 10 months.

• A medium-size system of 500,000 lines of code requires asoftware engineer to work 5,000 to 10,000 days or 20 to40 years.

⇒ Real-world software systems require many softwareengineers to work together to jointly develop asoftware system.


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To work together, the software engineers must

overcome three challenges, among others:

Communication CoordinationConceptualization

Solution:

• Processes and methodologies for analysis and design• UML for communication and coordination

• Tools that automate or support methodology steps.


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Software Life Cycle Activities

• Software processes and methodologies consist

of life cycle activities:

Cost

Software

Development

Process

Software

Quality

Assurance

Software

Project

Management

Time toMarketQualityProductivity


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1. Software Development Process

• A software development process transforms

the initial system concept into the operational

system running in the target environment.• It identifies the business needs, conducts a

feasibility study, and formulates the

requirements or capabilities that the systemmust deliver.

• It also designs, implements, tests, and deploysthe system to the target environment.


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The Waterfall Process

System Engineering

Software Requirements Analysis

Software Design

Coding & Unit Testing

Integration & Integration Testing

Acceptance Testing

Maintenance


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Example System Development – A Radio

Communication System (RCS)• The system is similar to a cellular network except that it

has only one high-power base station that serves an area

much larger than a cell in a cellular network. The systemrequirements specify the capabilities for the whole

system. 4 of the many system requirements identified:

– R1. The RCS shall allow mobile subscribers to initiate calls toother mobile subscribers and land-line telephones.

– R2. The RCS shall allow mobile subscribers to answer calls

from other subscribers.

– R3. The RCS shall provide call accounting to capture and

record mobile calls and bill to the subscriber accounts.

– R4. The RCS shall allow authorized account administrators to

manage subscriber accounts. 1-10


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System design using a block diagram

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• An architectural design of the RCS using a block

diagram.

• 3 subsystems: mobile unit, base station, and accountmanagement.


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Decomposition

• Requirement R1 involves mobile unit and base

station as well as hardware and software

functions. Sending a call request to the basestation is the function of a mobile unit.

Intercepting the request is a hardware function.

Checking the call request to ensure that it is asubscriber-to-subscriber call is a software

function. Therefore, the requirement R1 is

decomposed into the following:

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Decomposition

• R1.1. Mobile units shall include automatic number

identification (ANI) numbers when sending a call

request.

• R1.2. The base station shall verify the caller and

callee using the ANI numbers before setting up a call.

– R1.2.1. The software controller shall verify the caller and

callee, and instruct the hardware controller to set up a

connection when the verification is successful.

– R1.2.2. The hardware controller shall instruct the high-

power transceivers to establish an air-link connection underthe software control.

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Decomposition

• After decomposition, R1.1 is assigned to the mobile

unit.

• R1.2.1 is assigned to the base station softwarecontroller.

• Requirement R1.2.2 is assigned to the base station

hardware controller.• Similarly, R3 may be decomposed and assigned to the

appropriate subsystems.

• R4 is assigned to the account management subsystembecause it is a software-only requirement.

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Software Requirements Analysis

• Refines the system requirements allocated to the

software system. It also identifies other capabilities

for the software system. These and the refined system

requirements are specified in a software requirements

specification (SRS).

• For example, requirement R4 does not specify what

an authorized account administrator can do to manage

the accounts. Thus, the requirement is refined:

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Refined Requirement R4

• R4.1. The RCS shall allow an authorized account

administrator to create a subscriber account.


administrator to activate a subscriber account.


administrator to deactivate a subscriber account.


administrator to close a subscriber account.

• R4.5. The RCS shall allow an authorized accountadministrator to delete a subscriber account that is

already closed.

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Software Design

• Determines the software architecture, or the overall

structure, of the software system. It specifies the

subsystems, their relationships, the subsystems'

functions, interfaces, and how the subsystems interact

with each other.

• Designs the user interface.

• Specifies the information processing algorithms.

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Architectural design for the RCS

• N-tier architecture for the account management

system.

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2. Software Quality Assurance

Software quality assurance (SQA) ensures that

• the development activities are performed properly,

and• the software artifacts produced by the development

activities meet the software requirements and

desired quality standards.


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SQA Activities


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3. Software Project Management

• Software project management oversees the control

and administration of the development and SQA

activities.

• Project management activities include

– effort estimation

– project planning and scheduling

– risk management

– project administration, and

– others.

These activities ensure that the software system is

delivered on time and within budget.


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Object-Oriented Software Engineering

• Object-oriented software engineering (OOSE)is a specialization of software engineering.

• The object-oriented paradigm views the worldand systems as consisting of objects that relateand interact with each other.

• OOSE encompasses: – OO processes

– OO methodologies

– OO modeling languages – OO tools


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Software Engineering and Computer Science

Computer Science

• Pursue optimal solutions

• $$$ is not an important

consideration

• Programming in the small

• Technical issues

• Dealing with tame problems

• Foundations of software

engineering

Software Engineering

• Good enough is enough

• $$$ is an important factor

(PQCT – Productivity,Quality, Cost, Time to

market)

• Programming in the large• All issues and aspects

• Dealing with wicked

problems

• Building on top of computer

science and other disciplines

Documents

Software Engineering CH1 Slides