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Software Engineering
Zheng Li（李征）
Jing Wan（万静）
Why SE?
几乎所有与技术相关的工作都需要软件工程师
《2017年美国新兴职业报告》
LinkedIn’s 2017 U.S. Emerging Jobs Report
Couse Assessment
Total 40
▪ Lesson 32
▪ Project 8
TextBooks:
▪ 软件工程：实践者的研究方法(英文精编版第8版)
▪ Software Engineering:
A Practitioner’s Approach, 8/e Roger S.Pressman and Bruce R. Maxim
原出版社：McGraw-Hill Science/Engineering/Math
国内出版社：机械工业出版社
28 Feb 7 Mar 14 Mar 21 Mar 28 Mar
4 Apr 11 Apr 18 Apr 25 Apr 2 May
9 May 16 May 23 May 30 May
Couse Assessment
GRADING:
▪ Class collaboration (10%)
▪ Project (30%)
▪ Final Exam (60%)
Couse Assessment
Class Collaboration (10%)
▪ Attendance
▪ Contributing in the class discussions, if any
▪ Be active, but not too much
Project
TBA
Most of Slides are from the slide set to accompany
Software Engineering: A Practitioner’s Approach, 8/e
by Roger S. Pressman and Bruce R. Maxim
Slides copyright © 1996, 2001, 2005, 2009, 2014 by Roger S. Pressman
For non-profit educational use only
The course covers:
Introduction of Software Engineering
The Software Process
Modeling
Quality Management
Managing Software Projects
Topic Covered Today
The nature of software
Introduction of Software Engineering
Chapter 1: The Nature of Software
What is Software?
Software is:
1. instructions (computer programs) that when executed
provide desired features, function, and performance;
2. data structures that enable the programs to adequately
manipulate information and
3. documentation that describes the operation and use of
the programs.
These slides are designed to accompany Software Engineering:
A Practitioner’s Approach, 8/e (McGraw-Hill 2014). Slides
copyright 2014 by Roger Pressman.
14
Program = Data Structure + Algorithm
Software == Program ?
Programs + Associated documentation
such as requirements, design models and user
manuals.
What is Software?
Software
What software have you used?
Software Surrounds Our Civilization
Software Applications
System software
Application software
Engineering/Scientific software
Embedded software
Product-line software
Web/Mobile applications
AI software (robotics, neural nets, game playing)
18
What Does This Mean?
Software is getting more important
The Importance of software
Our civilization runs on software
软件是现代文明的重要基础
C++的设计者 Bjarne Stroustrup
Software Development
Software is developed or engineered,
it is not manufactured in the classical sense.
Software doesn't "wear out."
Although the industry is moving toward component-
based construction, most software continues to be
custom-built.
21
Wear vs. Deterioration
22
Legacy Software
Why must it change?
▪ software must be adapted to meet the needs of new computing
environments or technology.
▪ software must be enhanced to implement new business requirements.
▪ software must be extended to make it interoperable with other more
modern systems or databases.
▪ software must be re-architected to make it viable within a network
environment.
23
WebApps
Modern WebApps are much more than hypertext files with a few pictures
WebApps are augmented with tools like XML and Java to allow Web engineers including interactive computing capability
WebApps may standalone capability to end users or may be integrated with corporate databases and business applications
Semantic web technologies (Web 3.0) have evolved into sophisticated corporate and consumer applications that encompass semantic databases that require web linking, flexible data representation, and application programmer interfaces (API’s) for access
The aesthetic nature of the content remains an important determinant of the quality of a WebApp.
24
Mobile Apps
Reside on mobile platforms such as cell phones or tablets
Contain user interfaces that take both device characteristics and location attributes
Often provide access to a combination of web-based resources and local device processing and storage capabilities
Provide persistent storage capabilities within the platform
A mobile web application allows a mobile device to access to web-based content using a browser designed to accommodate the strengths and weaknesses of the mobile platform
A mobile app can gain direct access to the hardware found on the device to provide local processing and storage capabilities
As time passes these differences will become blurred
26
Cloud Computing
27
Cloud Computing
Cloud Computing
Cloud computing provides distributed data storage and processing resources to networked computing devices
Computing resources reside outside the cloud and have access to a variety of resources inside the cloud
Cloud computing requires developing an architecture containing both frontend and backend services
Frontend services include the client devices and application software to allow access
Backend services include servers, data storage, and server-resident applications
Cloud architectures can be segmented to restrict access to private data
29
Software Product Line
Software Product line is a set of software-intensive systems that
share a common set of features and satisfy the needs of a
particular market
These software products are developed using the same
application and data architectures using a common core of
reusable software components
A software product line shares a set of assets that include
requirements, architecture, design patterns, reusable components,
test cases, and other work products
A software product line allow in the development of many products
that are engineered by capitalizing on the commonality among all
products with in the product line
30
Chapter 2: Software Engineering
How Successful Have We Been?
Perform tasks more quickly and effectively
▪ Word processing, spreadsheets, e-mail
Support advances in medicine, agriculture,
transportation, multimedia education, and most
other industries
Many good stories
However, software is not without problems
火星气候探测者号的星际迷航
火星气候探测者号在1997年发射，在太空中飞行几个月以后，由于导航错误，最终在火星大气层解体。
阿丽亚娜5型运载火箭，昂贵的简单复制
1996年6月4日，阿丽亚娜5型运载火箭的首次发射点火后，火箭开始偏离路线，最终被逼引爆自毁，整个过程只有短短30秒。
http://www-users.math.umn.edu/~arnold/disasters/ariane5rep.html
阿丽亚娜5型运载火箭，昂贵的简单复制
阿丽亚娜5型运载火箭基于前一代4型火箭开发。4型火箭系统中，对一个水平速率的测量值使用了16位的变量及内存，而5型火箭的开发人员简单复制了这部分程序，而没有对新火箭进行数值的验证，结果发生了致命的数值溢出。发射后这个64位带小数点的变量被转换成16位不带小数点的变量，引发了一系列的错误，从而影响了火箭上所有的计算机和硬件，瘫痪了整个系统，
http://www-users.math.umn.edu/~arnold/disasters/ariane5rep.html
Northeast Blackout of 2003
Affected 10 million
people in Ontario,
Canada
Affected 40 million
people in 8 US
states
Financial losses of
$6 Billion USD
508 generating
units and 256
power plants shut
down
The alarm system in the energy management system failed
due to a software error and operators were not informed of
the power overload in the system
Apple 2015发布会
How Successful Have We Been?
A fault: occurs when a human makes a
mistake, called an error, in performing some
software activities
A failure: is a departure from the system’s
required behavior
Software Engineering
Some realities:
▪ a concerted effort should be made to understand the problem before a software solution is developed
▪ design becomes a pivotal activity
▪ software should exhibit high quality
▪ software should be maintainable
The seminal definition:
▪ [Software engineering is] the establishment and use of sound engineering principles in order to obtain economically software that is reliable and works efficiently on real machines.
Software Engineering
The IEEE definition:
▪ Software Engineering:
1. The application of a systematic, disciplined, quantifiable approach to
the development, operation, and maintenance of software; that is, the
application of engineering to software.
2. The study of approaches as in (1).
Relationship between CS and SE
Computer Science: focusing on computer hardware,
compilers, operating systems, and programming
languages; Computer science is concerned with theory
and fundamentals.
Software Engineering: a discipline that uses computer
and software technologies as a problem-solving tools;
Software engineering is concerned with the
practicalities of developing and delivering useful
software.
Relationship between CS and SE
A Layered Technology
50
Software Engineering
a “quality” focus
process model
methods
tools
A Process Framework
Process framework
▪ Framework Activities
work tasks
work products
milestones & deliverables
QA checkpoints
▪ Umbrella Activities
51
Framework Activities
Communication
Planning
Modeling
▪ Analysis of requirements
▪ Design
Construction
▪ Code generation
▪ Testing
Deployment
52
Umbrella Activities
Software project tracking and control
Risk management
Software quality assurance
Technical reviews
Measurement
Software configuration management
Reusability management
Work product preparation and production
53
Adapting a Process Model
the overall flow of activities, actions, and tasks and the interdependencies among them
the degree to which actions and tasks are defined within each framework activity
the degree to which work products are identified and required
the manner which quality assurance activities are applied
the manner in which project tracking and control activities are applied
the overall degree of detail and rigor with which the process is described
the degree to which the customer and other stakeholders are involved with the project
the level of autonomy given to the software team
the degree to which team organization and roles are prescribed
54
55
The Essence of Practice
Polya suggests:
1. Understand the problem (communication and analysis).
2. Plan a solution (modeling and software design).
3. Carry out the plan (code generation).
4. Examine the result for accuracy (testing and quality assurance).
56
Understand the Problem
Who has a stake in the solution to the problem? That is, who are the stakeholders?
What are the unknowns? What data, functions, and features are required to properly solve the problem?
Can the problem be compartmentalized? Is it possible to represent smaller problems that may be easier to understand?
Can the problem be represented graphically? Can an analysis model be created?
57
Plan the Solution
Have you seen similar problems before? Are there patterns that are recognizable in a potential solution? Is there existing software that implements the data, functions, and features that are required?
Has a similar problem been solved? If so, are elements of the solution reusable?
Can subproblems be defined? If so, are solutions readily apparent for the subproblems?
Can you represent a solution in a manner that leads to effective implementation? Can a design model be created?
58
Carry Out the Plan
Does the solution conform to the plan? Is source code traceable to the design model?
Is each component part of the solution provably correct? Has the design and code been reviewed, or better, have correctness proofs been applied to algorithm?
59
Examine the Result
Is it possible to test each component part of the solution? Has a reasonable testing strategy been implemented?
Does the solution produce results that conform to the data, functions, and features that are required? Has the software been validated against all stakeholder requirements?
Hooker’s General Principles
1: The Reason It All Exists
2: KISS (Keep It Simple, Stupid!)
3: Maintain the Vision
4: What You Produce, Others Will Consume
5: Be Open to the Future
6: Plan Ahead for Reuse
7: Think!
60
Software Myths
Affect managers, customers (and other non-technical
stakeholders) and practitioners
Are believable because they often have elements of
truth,
but …
Invariably lead to bad decisions,
therefore …
Insist on reality as you navigate your way through
software engineering
61
62
How It all Starts
SafeHome:▪ Every software project is precipitated by some business
need— the need to correct a defect in an existing application;
the need to the need to adapt a ‘legacy system’ to a changing business environment;
the need to extend the functions and features of an existing application, or
the need to create a new product, service, or system.
Email:lizheng@mail.buct.edu.cn
http://cist.buct.edu.cn/staff/zheng/
wanj@mail.buct.edu.cn
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