Pressman - Introduction to Software Engineering

7/31/2019 Pressman - Introduction to Software Engineering

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Part

1IntroductiontoSoftwareEngineering

copyright 1996,

2001, 2005R.S. Pressman & Associates,Inc.

For University UseOnlyMay be reproduced ONLY for student use at the university

levelwhen used in conjunction with Software Engineering: A Practitioner'sApproach. Any other reproduction or use is expressly

prohibited.This presentation, slides, or hardcopy may NOT be usedfor

short courses, industry seminars, or consulting

purposes.

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Softwares Dual

Role Software is aproduct Delivers computing

potential Produces, manages, acquires, modifies, displays,

ortransmitsinformation Software is a vehicle for delivering a

productSupports or directly provides system functionality

Controls other programs (e.g., an operatingsystem)

Effects communications (e.g., networking

software)2


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What is

Software?Software is a set of items orobjects

that form a configuration that

includes

programsdocuments

data ...

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What is

Software? software isengineered software doesnt wearout

software is complex

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Wear vs.

Deterioration increasedfailurerate due to sideeffectsFailu

re rate

change

actualcurve

idealizedcurve

Time

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Software

ApplicationsSystemsoftwareApplicationsoftwareEngineering/scientific

software

Embedded software

Product-line software

WebApps (Web

applications)

AI software6


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SoftwareNew Categories

Ubiquitous computingwireless networks

Netsourcingthe Web as a computingengine

Open sourcefree source code open tothe

computing community (a blessing, but also

apotential curse!)

Software for

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Legacy

Software Software must be adapted to meet the needs ofnewcomputing environments or

technology. Software must be enhanced to implement newbusinessrequirement

s. Software must be extended to make itinteroperablewith other more modern systems or

databases. Software must be re-architected to make it viable

withina networkenvironment.

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E-Type

Systems E-TypeSystems:Software that has been implemented in a real-

world

computing context and will therefore evolve overtime

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Software

EvolutionThe Law of Continuing Change (1974): E-type systems must be continually adapted else theybecomeprogressively less satisfactory.The Law of Increasing Complexity (1974): As an E-type system evolves its complexity increasesunlesswork is done to maintain or reduce it.The Law of Self Regulation (1974): The E-type system evolution process is self-regulatingwithdistribution of product and process measures close to normal.The Law of Conservation of Organizational Stability (1980): The average effective global activity rateinan evolving E-type system is invariant over product lifetime.The Law of Conservation of Familiarity (1980): As an E-type system evolves all associated with it,developers, sales personnel, users, for example, must maintain mastery of its content and behaviortoachieve satisfactory evolution.The Law of Continuing Growth (1980): The functional content of E-type systems must becontinuallyincreased to maintain user satisfaction over their lifetime.The Law of Declining Quality (1996): The quality of E-type systems will appear to be declining unlesstheyare rigorously maintained and adapted to operational environment changes.The Feedback System Law (1996): E-type evolution processes constitute multi-level, multi-loop,multi-agent feedback systems and must be treated as such to achieve significant improvement over anyreasonable base.

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Software

Myths Affect managers, customers (and othernon-technical stakeholders) and

practitioners Are believable because they often have elements

oftruth,

but

Invariably lead to bad

decisions,

therefore Insist on reality as you navigate your waythroughsoftware

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Management

Myths We already have a book of standardsandprocedures for building software. It does provide

my

people with everything they need to know If my project is behind the schedule, I alwayscanadd more programmers to it and catch up

(a.k.a. The Mongolian Hordeconcept) If I decide to outsource the software project to a

third party, I can just relax: Let them build it, andI

will just pocket my profits 1

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Customer

Myths A general statement of objectives is sufficientto

begin writing programs - we can fill in the

detailslater Project requirements continually change butthischange can easily be accommodated

because

software is flexible

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Practitioners

Myths Lets start coding ASAP, because once we writetheprogram and get it to work, our job is done

Until I get the program running, I have no way ofassessingits quality

The only deliverable work product for a successfulprojectis the working program

Software engineering is baloney. It makes us createtonsof paperwork, only to slow us down

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Pressman - Introduction to Software Engineering