Transcript Lecture for Chapter 1, Introduction to Software Engineering

Profession
A Physician, a Civil Engineer and a Computer Scientist were arguing
about what was the oldest profession in the world.

The Physician remarked,
"Well, in the Bible, it says that God created Eve from a rib taken out of Adam.
This clearly requires surgery, and so I can rightly claim that mine is the oldest
profession in the world."

The Civil Engineer interrupted, and said,
" But even earlier in the book of Genesis, it states that God created the order of
the heavens and the earth from out of the chaos. This was the first and certainly
the most spectacular application of civil engineering. Therefore, fair doctor,
you are wrong; mine is the oldest profession in the world.“

The Computer Scientist leaned back in the chair, smiled and
then said confidently,
"Ah, but what do you think created the chaos ? "
Bernd Bruegge & Allen H. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Using UML, Patterns, and Java
Object-Oriented Software Engineering
Chapter 1: Introduction
Objectives of the Class

Appreciate Software Engineering:
 Build complex software systems in the context of frequent change

Understand how to
 produce a high quality software system within time
 while dealing with complexity and change


Acquire technical knowledge (main emphasis)
Acquire managerial knowledge

Understand the Software Lifecycle
 Process vs Product
 Learn about different software lifecycles
 Greenfield Engineering – from scratch,
Interface Engineering – a kind of Reengineering for legacy systems,
Reengineering – [Hammer & Champy, 1993]
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Acquire Technical Knowledge


Understand System Modeling
Learn About Modeling
Using (~20% and some) Aspects of UML (Unified Modeling Language)

Learn about modeling at different phases ofBrugge’s
software lifecycle:
 Requirements Elicitation [Chap. 4] –---------------------




(Requirements) Analysis* [Chap 5] ----------------------Architectural Design [Chap 6 & 7] ----------------------Object/Component Design [Chap 8] ---------------------Coding [Chap 10]
---------------------Testing [Chap 11]
----------------------
Deliverable 1
Deliverable 2
Deliverable 3
Deliverable 4
Deliverable 5
Deliverable 6
(during demo)
* An old school of thought mixing the domain model with the solution model, being design-oriented, and in a
Waterfall fashion.

Learn about Traceability among Models

Learn how to use Tools: CASE (Computer Aided Software Engineering)
e.g., Rational Rose
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Readings



Required:
 Bernd Bruegge, Allen Dutoit: “Object-Oriented Software
Engineering: Using UML, Patterns, and Java”, Prentice Hall, 2003.
Recommended:
 Applying UML and Patterns: An Introduction to Object-Oriented
Analysis and Design and the Unified Process, 2nd ed., C. Larman
 Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides:
“Design Patterns”, Addison-Wesley, 1996.
 Grady Booch, James Rumbaugh, Ivar Jacobson, “The Unified
Modeling Language User Guide”, Addison Wesley, 1999.
 K. Popper, “Objective Knowledge, an Evolutionary Approach,
Oxford Press, 1979.
Additional books may be recommended during individuals lectures
Lecture Notes will adapt Bruegge’s,
but with additional points and questions
possibly from very different perspectives.
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Outline of Today’s Lecture


Software Engineering – Why, What and How?
Modeling complex systems
 Functional vs. object-oriented decomposition


Software Lifecycle Modeling
Reuse:
 Design Patterns
 Frameworks

Concluding remarks
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Why Software Engineering?
9 software projects totaling $96.7 million: Where The Money Went
[Report to Congress, Comptroller General, 1979]
Delivered, but never
successfully used
45%
Used as delivered
2%
Usable w. rework
3%
Used w. extensive rework,
but later abandoned
20%
Paid for, but
not delivered
30%
Object-Oriented
Software Engineering:
UML, Patterns, andReport)
Java
Take a look at the Standish
Report
(TheUsing“Chaos”
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Software Engineering: A Problem Solving Activity


Analysis: Understand the nature of the problem and break the
problem into pieces
Synthesis: Put the pieces together into a large structure
For problem solving we use
 Techniques (methods):
 Formal procedures for producing results using some well-defined
notation

Methodologies:
 Collection of techniques applied across software development and
unified by a philosophical approach

Tools:
 Instrument or automated systems to accomplish a technique
Isn’t there something moreObject-Oriented
fundamental
than
Software Engineering:
Usingproblem
UML, Patterns, and“solving”?
Java
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Software Engineering: Definition
Software Engineering is a collection of techniques,
methodologies and tools that help
with the production of



a high quality software system
with a given budget
before a given deadline
while change occurs.
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Scientist vs Engineer

Computer Scientist
 Proves theorems about algorithms, designs languages, defines
knowledge representation schemes
 Has infinite time…

Engineer
 Develops a solution for an application-specific problem for a client
 Uses computers & languages, tools, techniques and methods

Software Engineer
 Works in multiple application domains
 Has only 3 months...
 …while changes occurs in requirements and available technology
Isn’t there something more fundamental about “Software” Engineer?
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Factors affecting the quality of a software system

Complexity:
 The system is so complex that no single programmer can understand it
anymore
 The introduction of one bug fix causes another bug

Change:
 The “Entropy” of a software system increases with each change: Each
implemented change erodes the structure of the system which makes the
next change even more expensive (“Second Law of Software
Dynamics”).
 As time goes on, the cost to implement a change will be too high, and
the system will then be unable to support its intended task. This is true
of all systems, independent of their application domain or technological
base.
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Complex Server Connections
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Complex Message Flow
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Dealing with Complexity
1.
2.
3.
Abstraction
Decomposition
Hierarchy
What is this?
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1.
1. Models are used to provide abstractions
2.
3.




Abstraction
Decomposition
Hierarchy
Inherent human limitation to deal with complexity
 The 7 +- 2 phenomena
Chunking: Group collection of objects
Ignore unessential details: => Models
System Model:
What does this refer to?
 Object Model: What is the structure of the system? What are the objects and how
are they related?
 Functional model: What are the functions of the system? How is data flowing
through the system?
 Dynamic model: How does the system react to external events? How is the event flow
in the system ?
In UML?

Task Model:
 PERT Chart: What are the dependencies between the tasks?
 Schedule: How can this be done within the time limit?
 Org Chart: What are the roles in the project or organization?

Issues Model:
 What are the open and closed issues? What constraints were posed by the client?
What resolutions were made?
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Model-based software Engineering:
Code is a derivation of object model
Is this a “problem”?
Problem Statement : A stock exchange lists many companies.
Each company is identified by a ticker symbol
Analysis phase results in object model (UML Class Diagram):
*
StockExchange
Lists
*
Company
tickerSymbol
Implementation phase results in code
public class StockExchange
{
public Vector m_Company = new Vector();
Where is the design, then?
};
public class Company
{
public int m_tickerSymbol
public Vector m_StockExchange = new Vector();
};
A good software engineer writes as little code as possible
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Example of an Issue: Galileo vs the Church

What is the center of the Universe?
 Church: The earth is the center of the universe. Why? Aristotle says
so.
 Galileo: The sun is the center of the universe. Why? Copernicus
says so. Also, the Jupiter’s moons rotate round Jupiter, not around
Earth.
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Issue-Modeling
Issue:
What is the
Center of the
Universe?
Resolution (1998):
The church declares
proposal 1 was wrong
Proposal2:
The sun!
Proposal1:
The earth!
Pro:
Resolution (1615):
The church
decides proposal 1
is right
Con:
Jupiter’s moons rotate
around Jupiter, not
Aristotle
says so.
Copernicus
says so.
around Earth.
Pro:
Change will disturb
the people.
Bernd Bruegge & Allen H. Dutoit
Pro:
Object-Oriented Software Engineering: Using UML, Patterns, and Java
Anything missing?
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1.
2. Decomposition
2.
3.


Abstraction
Decomposition
Hierarchy
A technique used to master complexity (“divide and conquer”)
Functional decomposition
 The system is decomposed into modules
 Each module is a major processing step (function) in the application
domain
 Modules can be decomposed into smaller modules

Object-oriented decomposition
 The system is decomposed into classes (“objects”)
 Each class is a major abstraction in the application domain
 Classes can be decomposed into smaller classes
Which decomposition is the right one?
Bernd Bruegge & Allen H. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Functional Decomposition
System
Function
Read Input
Read Input
Transform
Load R10
Transform
Top Level functions
Produce
Output
Level 2 functions
Produce
Output
Add R1, R10
Is this about the requirements
orSoftware
a design?
Object-Oriented
Engineering: Using UML, Patterns, and Java
Bernd Bruegge & Allen H. Dutoit
Level 1 functions
Machine Instructions
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Functional Decomposition



Functionality is spread all over the system
Maintainer must understand the whole system to make a single
change to the system
Consequence:
 Codes are hard to understand
 Code that is complex and impossible to maintain
 User interface is often awkward and non-intuitive

Example: Microsoft Powerpoint’s Autoshapes
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Functional Decomposition: Autoshape
Autoshape
Mouse
click
Change
Rectangle
Draw
Change
Change
Oval
Change
Circle
Draw
Rectangle
Draw
Oval
Draw
Circle
How is this different from OO?
How are Functionally-Oriented systems different from OO systems?
Bernd Bruegge & Allen H. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
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OO-Decomposition - Class Identification


Class identification is crucial to object-oriented modeling
Basic assumption:
1. We can find the classes for a new software system: We call this
Greenfield Engineering
2. We can identify the classes in an existing system: We call this
Reengineering
3. We can create a class-based interface to any system: We call this
Interface Engineering

Why can we do this? Philosophy, science, experimental
evidence

What are the limitations? Depending on the purpose of the
system different objects might be found
 How can we identify the purpose of a system?
Then, depending on the purpose, could a functional decomposition be better than an OO decomposition?
Which
is UML
functional- or OO-decomposition?
Bernd Bruegge
& Allenfor,
H. Dutoit
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Model of an Eskimo
Eskimo
Size
Dress()
Smile()
Sleep()
*
Shoe
Size
Color
Type
Wear()
Bernd Bruegge & Allen H. Dutoit
Coat
Size
Color
Type
Wear()
Is this a good model?
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Iterative Modeling then leads to ....
lives in
Cave
Lighting
Enter()
Leave()
Eskimo
Size
Dress()
Smile()
Sleep()
moves
around
Outside
Temperature
Light
Season
Hunt()
Organize()
*
Entrance
Windhole
Diameter
MainEntrance
Size
but is it the right model?
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Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Alternative Model: The Head of an Indian
Indian
Hair
Dress()
Smile()
Sleep()
Ear
Size
listen()
*
Bernd Bruegge & Allen H. Dutoit
Face
Nose
smile()
close_eye()
Mouth
NrOfTeeths
Size
open()
speak()
Is this a good model?
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1.
3. Hierarchy
2.
3.

Abstraction
Decomposition
Hierarchy
2 important hierarchies
 "Part of" hierarchy
 "Is-kind-of" hierarchy
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Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Part of Hierarchy
Computer
I/O Devices
CPU
Memory
Cache
ALU
Program
Counter
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Is-Kind-of Hierarchy (Taxonomy)
Cell
Muscle Cell
Striate
Smooth
Blood Cell
Red
White
Nerve Cell
Cortical
Pyramidal
Any issue?
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So where are we right now?

Three ways to deal with complexity:
 Abstraction
 Decomposition
 Hierarchy

Object-oriented decomposition is a good methodology
 Unfortunately, depending on the purpose of the system, different
objects can be found

How can we do it right?
 Many different possibilities
 Our current approach: Start with a description of the functionality
(Use case model), then proceed to the object model
 This leads us to the software lifecycle
*An old school of thought mixing the domain model with the solution model, being design-oriented, and in a Waterfall fashion.
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Object-Oriented Software Engineering: Using UML, Patterns, and Java
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Software Lifecycle Definition

Software lifecycle:
 Set of activities and their relationships to each other to support the
development of a software system

Typical Lifecycle questions:
 Which activities should I select for the software project?
 What are the dependencies between activities?
 How should I schedule the activities?
Bernd Bruegge & Allen H. Dutoit
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Software Lifecycle Activities
Deliverable 0
Deliverable 1
Deliverable 2
Deliverable 3
Deliverable 4
Deliverable 5
Deliverable 6
Requirements
Elicitation
Requirements
Analysis
System
Design
Object
Design
Implementation
Testing
Expressed in
Terms Of
Structured By
Implemented
By
Realized By
Verified
By
class...
class...
class...
Use Case
Model
Application
SubSystems
Domain
Objects
Solution
Domain
Objects
Each
activity produces one or
more models
Bernd Bruegge & Allen H. Dutoit
Object-Oriented Software Engineering: Using UML, Patterns, and Java
Source
Code
?
class.... ?
Test
Cases
33
Reusability: Design Patterns and Frameworks

Design Pattern:
 A small set of classes that provide a template solution to a recurring
design problem
 Reusable design knowledge on a higher level than data structures
(link lists, binary trees, etc)

Framework:
 A moderately large set of classes that collaborate to carry out a set
of responsibilities in an application domain.



Examples: User Interface Builder
Provide architectural guidance during the design phase
Provide a foundation for software components industry
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Summary

Software engineering is a problem solving activity
 Developing quality software for a complex problem within a limited
time while things are changing

There are many ways to deal with complexity






Modeling, decomposition, abstraction, hierarchy
Issue models: Show the negotiation aspects
System models: Show the technical aspects
Task models: Show the project management aspects
Use Patterns: Reduce complexity even further
Many ways to deal with change
 Tailor the software lifecycle to deal with changing project
conditions
 Use a nonlinear software lifecycle to deal with changing
requirements or changing technology
 Provide configuration management to deal with changing entities
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Additional Slides
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Software Production has a Poor Track Record
Example: Space Shuttle Software



Cost: $10 Billion, millions of dollars more than planned
Time: 3 years late
Quality: First launch of Columbia was cancelled because of a
synchronization problem with the Shuttle's 5 onboard
computers.
 Error was traced back to a change made 2 years earlier when a
programmer changed a delay factor in an interrupt handler from
50 to 80 milliseconds.
 The likelihood of the error was small enough, that the error caused
no harm during thousands of hours of testing.

Substantial errors still exist.
 Astronauts are supplied with a book of known software problems
"Program Notes and Waivers".
Object-Oriented Software
Engineering:
Using UML,
Patterns, and Java Report)
Take a look at the Standish
Report
(The
“Chaos”
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Reusability


A good software design solves a specific problem but is general
enough to address future problems (for example, changing
requirements)
Experts do not solve every problem from first principles
 They reuse solutions that have worked for them in the past

Goal for the software engineer:
 Design the software to be reusable across application domains and
designs

How?
 Use design patterns and frameworks whenever possible
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Patterns are used by many people

Chess Master:

 Openings
 Middle games
 End games

Writer
 Tragically Flawed Hero
(Macbeth, Hamlet)
 Romantic Novel
 User Manual

Software Engineer
 Composite Pattern: A collection
of objects needs to be treated
like a single object
 Adapter Pattern (Wrapper):
Interface to an existing system
 Bridge Pattern: Interface to an
existing system, but allow it to
be extensible
Architect
 Office Building
 Commercial Building
 Private Home
Bernd Bruegge & Allen H. Dutoit
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