20 March XML Extreme Programming

Customization Separation of customization from code Create family of applications instead of a single one Design from the start Currently favored: XML

XML What is it? Tools How to use it?

What is XML?  XML - eXtensible Markup Language  A "standard/specification" for describing data with markup tags  Tags can describe data or a structure  XML - cornerstone of a set of technologies  XML can be used alone  Related technologies for most effective use

History of XML  Built on other technologies  GML and SGML – (Standard) Generalized Markup Language: 1960s  Before there was Word and WYSIWYG editors  HTML - HyperText Markup Language  W3C (World Wide Web Consortium) standard

.ce Introduction.ju ss The work of authors, publishers, and researchers involves, in varying degrees, three recognizable text Formatting commands:.ce center next line.ju justify right margin.ll line length.ss single spacing Script (GML)Example

Tags  Focus on data description and structure  Element -- a pair of tags with content  Attribute -- specific information about an element  Allow creation of XML Dialects  SMIL -- for multimedia (RealPlayer Multimedia players)  WML -- Wireless WAP-phones  XHTML -- XMLized version of HTML  MathML -- for mathematics  HEML -- historical events  Hundreds of dialects Hundreds of dialects

HTML XML Uses & style Markup describes text Focus on presentation Data is text (limited reuse) (Relatively) fixed set of tags Loose syntax End tags assumed Nesting errors affect display Simple and complete Single use - for Web Uses & style Markup describes information Focus on data structure Data retains meaning Extensible - can define new tags Stringent syntax End tags required Element nesting enforced Uses related technologies Highly reusable documents

Related Technologies XML schema (XSD replaced DTD) XML schema provides the syntax defines way elements and attributes represented in a XML document eXtended Stylesheet Language (XSL)XSL enables data reuse transform XML into other XML HTML format XML for presentation (rendering) Fonts, size, color, alignment,... Rules for ordering

Tools XML Parser XSL Processor Lots and lots of them Should you use them?

How to Use XML Key uses Separation of changeable decisions Need for multiple forms Before you invent your own tags, are there relevant ones that you can appropriate? Use of attributes versus elements continuing discussion

The Goal of Software Engineering The right software, delivered defect free, on time and on cost, every time.

Software Engineering History First key conference in 1968 Became important because of perceived software crisis in productivity Cost and budget overruns (OS/360) Morphed to issues of quality Financial implications (BoNY) Safety (Therac)

BoNY (1985) BoNY (Bank of New York): Nation’s largest clearer of government securities Software to track Federal securities transactions wrote new information on top of old. Feds debited the bank for each transaction but bank did not know who owed it how much. 90 minutes => $32 Billion overdraft !

Cost of Bug Bank had to borrow $24 bill from federal reserves. Interest paid ~$5 mill for 1 day. (Annual earnings of bank ~$120 mill) BoNY share prices dropped by 25 cents Federal funds rate dropped from 8.4% to 5.5% System down for 28 hours. Fear of financial crisis caused increase in price of platinum!

Cause of bug Message buffer counter at BoNY system was 16-bit long. Counters at Fed (and other banks) 32 bit. More than 32,000 transactions that morning! =>Counter overflow Securities database corrupted.

The Drama continues… Trying to correct it – they copied corrupted data over the backup. Lost a few hours because of this. Does code for error recovery get tested at all?

Therac-25 ( ) Medical linear accelerator Used to zap tumors with high energy beams. Electron beams for shallow tissue or x-ray photons for deeper tissue. Eleven Therac-25s were installed: Six in Canada Five in the United States

Therac-25 Turntable Counterweight Field Light Mirror Beam Flattener (X-ray Mode) Scan Magnet (Electron Mode) Turntable

Therac-25 Changes from Therac-20 Used new “double pass” technique to accelerate electrons…more deadly Machine itself took up less space Software coupled to the rest of the system and responsible for safety checks. Hardware safety interlocks removed. “Easier to use”

What Happened? Six patients were delivered severe overdoses of radiation between 1985 and Four of these patients died. Why? The turntable was in the wrong position. Patients were receiving x-rays without beam-scattering.

What caused that to happen? Race conditions. Overflow error. The turntable position was not checked every 256th time the “Class3” variable was incremented. No hardware safety interlocks. Non-descriptive error messages. “Malfunction 54” “H-tilt” User-override-able error modes.

Source of the Bug Incompetent engineering. Design Troubleshooting Virtually no testing of the software. The safety analysis excluded the software! No usability testing.

That’s Why We Care Now, back to history…

1960’s 60’s “Cowboys” wrote software anyway that they could Difference between best programmers and worst as high as 28:1 (many sources) 1968 Edsger Dijkstra, “GOTO Statement Considered Harmful” (CACM)GOTO Statement Considered Harmful Recognition that rules can improves the average programmer The start of software engineering?

Structuring Software Development Few rules helped immensely Good rules and practices developed over the 70’s and 80’s If a few rules are good, more are better… Late 80’s, major focus on process as a key to quality ISO 9000 Malcolm Baldridge National Quality Award Why not apply to software development?

ISO 9000 What is ISO? International body 150 national standards organization US: ANSI Primarily technical standards Recent years has broadened its scope Generic management system standards First published in 1987 Revision in 2000 Compendium of best practices Not the process but the management of the process

Which brings us back to What is part of software engineering?

The 4 P’s of Software Engineering People: those doing it Product: what is produced Process: the manner in which it is done Project: the doing of it

Models of Software Development Process or people oriented Early Watts Humphrey work: people, later process Different balances from each model Number of iterations Waterfall Spiral Agile

Software Craftmanship Software craftsmanship (McBreen 2001)McBreen 2001 Craft of writing software Craft of using software Distinguish from software engineering Scope Rigor Relevant distinction?

Product Sales brochure Use cases and requirements Design document: from architecture to detailed design Fully documented code Test plan and tools Manuals Users Administrators

Process Software Engineering Steps Concept Requirements Architecture Design Implementation Unit test Integration System test Maintenance Software Engineering Processes Reviews and Inspections

Software Engineering Processes Differ by how often you do the steps Points on the spectrum Differences in overhead Three fundamental models Waterfall Spiral Iterative Two widely used models Rational Unified Process (a.k.a. Unified Software Development Process) Extreme Programming

Integrated Product Development: The IBM Approach Originated at GE Key principles Cross-functional teams at all phases Phased approval Example checkpoints Concept Plan Ship Sunset

Rational Unified Process Iterations within phases 4 phases Inception (interaction with stakeholders) Elaboration (architecture and functions) Construction (initial operational) Transition (completed product) Core workflows for each iteration Requirements Analysis (part of Requirements) Design Implementation (includes Integration) Test

Unified Process Matrix ElaborationInceptionConstructionTransition Requirements Analysis Design Implemen- tation Test

Extreme Programming Complete development process First code drop is 2-3 weeks after start Customer a part of the development team Iterative development to the max Derive requirements with customer through hands-on experimentation Agile methodology

Why XP? Companies started codifying their practices Large documents and people to manage them Rise of the project manager “Honored in the breach” More large projects and more late or failed projects

1995 Standish Group Study 50% software projects challenged 2x budget 2x completion time 2/3 planned function 30% impaired Scrapped 20% success pdf

Agile Methodologies Keep only those rules and processes that help Antidote to bureaucracy License to hack Key characteristics Adaptive People-oriented

Extreme Programming: History Kent Beck considered the inventor Ideas developed in the early 90’s First project at Daimler Chrysler in 1996

XP Bills of Rights Developer has a right to Clear requirements and priorities Determine how long a requirement will take to implement Revise estimates Always produce quality code Customer has a right to An overall plan See progress in a running system Change requirements and priorities Be informed of changes to schedule and have input as to how to adapt Cancel in the middle and still have something to show for the investment

XP Bills of Rights Developer has a right to Clear requirements and priorities Determine how long a requirement will take to implement Revise estimates Always produce quality code Customer has a right to An overall plan See progress in a running system Change requirements and priorities Be informed of changes to schedule and have input as to how to adapt Cancel in the middle and still have something to show for the investment

XP Value System Communication Focus on people, not documentation Simplicity Of process and code Feedback Mechanism to make useful progress Courage To trust in people

People Most important factor in the quality of software is the quality of the programmers If your life depended on a particular piece of software, what would you want to know about it? Bollinger (2001): that the person who wrote it was “both highly intelligent and possessed by an extremely rigorous, almost fanatical desire to make their program work the way it should.”

Knowledge Workers … prefer closed offices but communicate better in open ones congregate in particular geographical areas move around in the course of their work collaborate concentrate work in the office communicate with people who are close by don't care about facilities gewgaws Davenport, Why Office Design Matters 2005Why Office Design Matters

Extreme Programming Project