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Slide 1.1

The McGraw-Hill Companies, 2002

Object-Oriented andClassical Software

Engineering

Fifth Edition, WCB/McGraw-Hill, 2002

Stephen R. Schachsrs@vuse.vanderbilt.edu

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Slide 1.2

The McGraw-Hill Companies, 2002

CHAPTER 1

SCOPE OFSOFTWARE ENGINEERING

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Slide 1.3

The McGraw-Hill Companies, 2002

Outline

q Historical aspects

q Economic aspects

q Maintenance aspects

q Specification and design aspects

q Team programming aspects

q The object-oriented paradigm

q Terminology

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Slide 1.4

The McGraw-Hill Companies, 2002

Scope of Software Engineering

q Historical Aspects

1968 NATO Conference, Garmisch

Aim: to solve the Software Crisis

Software is delivered

Late Over budget

With residual faults

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Slide 1.5

The McGraw-Hill Companies, 2002

Scope of Software Engineering (contd)

q Why cannot bridge-building techniques

be used to build operating systems?

Attitude to collapse

Imperfect engineering

Complexity Maintenance

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Slide 1.6

The McGraw-Hill Companies, 2002

Conclusion

q Software Engineering is not Engineering

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Slide 1.7

The McGraw-Hill Companies, 2002

Economic Aspects

q Economically viable techniques

q Coding method CMnew is 10% faster than currently

used method CMold. Should it be used?

Common sense answer

Of course!

Software Engineering answer

Consider the effect of CMnew on maintenance

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Slide 1.8

The McGraw-Hill Companies, 2002

Maintenance Aspects

q Software Life Cycle

The way we produce software, including

The life-cycle model

The individuals

CASE tools

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Slide 1.9

The McGraw-Hill Companies, 2002

Life-cycle model

1. Requirements phase

2. Specification phase

3. Design phase

4. Implementation phase

5. Integration phase (in parallel with 4)

6. Maintenance phase

7. Retirement

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Slide 1.10

The McGraw-Hill Companies, 2002

Approximate Relative Cost of Each Phase

q 19761981 data

q Maintenance constitutes 67% of total cost

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Slide 1.11

The McGraw-Hill Companies, 2002

Comparative Relative Cost of Each Phase

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Slide 1.12

The McGraw-Hill Companies, 2002

Good and Bad Software

q Good software is maintainedbad software

is discarded

q Different types of maintenance

Corrective maintenance [about 20%]

Enhancement Perfective maintenance [about 60%]

Adaptive maintenance [about 20%]

q Effect of CMnew on maintenance

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Slide 1.13

The McGraw-Hill Companies, 2002

Specification and Maintenance Faults

q 60 to 70 percent of faults are specification

and design faults

q Data of Kelly, Sherif, and Hops [1992]

1.9 faults per page of specification

0.9 faults per page of design 0.3 faults per page of code

q Data of Bhandari et al. [1994]

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Slide 1.14

The McGraw-Hill Companies, 2002

Specification and Maintenance Faults (contd)

q Faults at end of the design phase of the

new version of the product

13% of faults from previous version of product

16% of faults in new specifications

71% of faults in new design

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Slide 1.15

The McGraw-Hill Companies, 2002

Cost to Detect and Correct a Fault

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Slide 1.17

The McGraw-Hill Companies, 2002

The Object-Oriented Paradigm

q The structured paradigm had great successes

initially It started to fail with larger products (> 50,000 LOC)

q Maintenance problems (today, up to 80% ofeffort)

q Reason: structured methods are Action oriented (finite state machines, data flow

diagrams); or

Data oriented (entity-relationship diagrams,

Jacksons method); But not both

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Slide 1.18

The McGraw-Hill Companies, 2002

The Object-Oriented Paradigm (contd)

q Both data and actions are of equal importanceq Object:

Software component that incorporates both dataand the actions that are performed on that data

q Example: Bank account

Data: account balance

Actions: deposit, withdraw, determine balance

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Slide 1.19

The McGraw-Hill Companies, 2002

Structured versus Object-Oriented Paradigm

q Information hidingq Responsibility-driven design

q Impact on maintenance, development

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Slide 1.20

The McGraw-Hill Companies, 2002

Key Aspects of Object-Oriented Solution

q Conceptual independence

Encapsulation

q Physical independence

Information hiding

q Impact on development Physical counterpart

q Impact on maintenance

Independence effects

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Slide 1.21

The McGraw-Hill Companies, 2002

Responsibility-Driven Design

q Also called Design by Contract

q Send flowers to your aunt in Iowa City

Call 1-800-FLOWERS

Where is 1-800-FLOWERS?

Which Iowa City florist does the delivery? Information hiding

q Object-oriented paradigm

Send a message to a method [action] of an object

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Slide 1.22

The McGraw-Hill Companies, 2002

Transition From Analysis to Design

q

Structured paradigm: Jolt between analysis (what) and design (how)

q Object-oriented paradigm:

Objects enter from very beginning

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Slide 1.23

The McGraw-Hill Companies, 2002

Analysis/Design Hump

q Systems analysis

Determine what has to be done

q Design

Determine how to do it

Architectural designdetermine modules Detailed designdesign each module

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Slide 1.24

The McGraw-Hill Companies, 2002

Removing the Hump

q Object-oriented analysis

Determine what has to be done

Determine the objects

q Object-oriented design

Determine how to do it Design the objects

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Slide 1.25

The McGraw-Hill Companies, 2002

In More Detail

q Objects enter here

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Slide 1.26

The McGraw-Hill Companies, 2002

Warning

q Do not use the object-paradigm to enhance a

product developed using the structured paradigm Water and oil do not mix

q Exception: if the new part is totally disjoint

Example: adding a GUI (graphical user interface)

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Slide 1.27

The McGraw-Hill Companies, 2002

Terminology

q Quality

q Program, system, product

q Methodology, paradigm

q Method and technique

q Client, developer, user

q Bug A bug crept into the code

instead of I made a mistake

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Slide 1.28

The McGraw-Hill Companies, 2002

Object-Oriented Terminology

q Data component of an object

State variable

Instance variable (Java)

Field (C++)

Attribute (generic)q Action component of an object

Member function (C++)

Method (generic)

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Slide 1.29Object-Oriented Terminology (contd)

q C++: A member is either an

Attribute (field), or a

Method (member function)

q Java: A field is either an

Attribute (instance variable), or a Method