Umw Software Engineering Guest Lecture 05 Sep2007

Software Engineering:Theory and Practice

David Hyland-Wooddavid@zepheira.com, dhylandw@umw.edu

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Agenda

Theory

Practice

Understanding before doing

Beautiful code

Guessing the future

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Theory

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Lost in Terminology

Software metric primitives are non-isomorphic:

“defect”

“resource”

“programmer”

“time”

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Lost in Terminology

Entailment?I need help *FINDING*

my tail!

http://www.flickr.com/photos/efleming/237379205/

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60/60 Rule

Cost of softwareover entire lifecycle

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Understanding and Bugs

Causes of bugs:The greatest number of bugs

occur in requirements specification and design

Cost of repair:The greatest cost is incurred in correcting requirements bugs

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Three Fallacies

The Fallacy of Perfect Knowledge:It is possible to capture complete, non-conflicting requirements with sufficient attention to detail.

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Three Fallacies

The Fallacy of Perfect Knowledge:It is possible to capture complete, non-conflicting requirements with sufficient attention to detail.

Users generally do not know what is possible, do not agree among themselves and may not understand all aspects of their system.

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Three Fallacies

The Fallacy of the Big Round Ball:Requirements don’t change appreciably after delivery or can be controlled.

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Three Fallacies

The Fallacy of the Big Round Ball:Requirements don’t change appreciably after delivery or can be controlled.

Requirements change continuously as software ages. This should be seen as a benefit.

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Three Fallacies

The Fallacy of Perfect Execution:It is possible to create flawless code with sufficient attention to detail.

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Three Fallacies

The Fallacy of Perfect Execution:It is possible to create flawless code with sufficient attention to detail.

We need to admit that arbitrary logic is hard to verify in the general case, hard or impossible to fully test and, combined with inconsistent or changing requirements, hard to trace programmer intent.

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Practice

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(With apologies to S. Gross)

The Real World isSoft and Mushy

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A History of Silos

1970s 1980s 1990s

$ cat foo.txt | grep blah | sort

A neat little package Client-Server The Early Web

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The Next Great Leap

Web of Data

Extending theUniversal Client

Expanding theUniversal Connection

Providing theUniversal Database

Explaining the Logic

Ubiquitous,reusable applications

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Examples

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New Applications

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And More....

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Understanding Before Doing

Some material adapted from Kurt Akeley,General Manager, Microsoft Research Asia, 21 July 2006

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The Cost of Failure

“If you can’t code something, it is because you don’t understand it” -- Jon Butler

Sadly, the reverse is not true.

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Writing Facilitates Understanding

The process of writing is the process of refining one’s thoughts.

Refinement of thought applies to writing both words and code.

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“This, surely, is the secret of Lincoln’s eloquence. He not only read aloud, to think his way into sounds, but wrote as a way of ordering his thought.”

— Garry WellsIn Lincoln at GettysburgSimon & Shuster, 1992

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“Don’t worry if you don’t understand this book completely on the first reading. We didn’t understand it all on the first writing!”

— Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (aka The Gang of Four)In Design Patterns, Addison Wesley, 1995

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Write Up

ResultsDone?

Research &

Develop

Yes

No

Stop

?

Write First

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Beautiful Code

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What Does Your CodeLook Like?

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A Hardware Analogy

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Another Hardware Analogy

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“Higher-level programming ... allows good programmers to write more beautiful code, and bad programmers to write stuff that's even uglier than it used to be.”

— Andy Oram & Greg Wilson (eds.)Beautiful Code, O’Reilly, 2007

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Creating Beautiful Code

Beauty counts“Omit needless words!” -- Strunk and WhiteDevelop a habit of refactoring for both

design and maintenanceThe art changes; keep up

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Guessing the Future

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Writing Business Applications

1970s 1980s 1990s 2000s

Code written

Dataformatted

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Same Data, Different Forms

HumanReadable

MachineReadable

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Getting to the Web 2.0+ Enterprise

Thanks to CBS Paramount Television. TM & Copyright © 2007 CBS Studios Inc.

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2000 3B

2001 6B

2002 12B

200324B

40,000 BCEcave paintings

bone tools

writingpaper

printing

electricity, telephone

transistorcomputing

Internet(DARPA) The web

GIGABYTES

2000 rich contentSource: UC Berkeley School of Information Management and Systems,Robert Steele, CEO OSS, Inc.

The Information Economy

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Don’t Focus on Code

Solve problems insteadStart thinking about information spacesNavigating

Creating

Extracting From

Extending

Abstraction, abstraction, abstraction

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