Alistair Cockburn©Humans and Technology, Inc., 2000-2003 Slide 1 Agile Use Cases ( Writing...

Alistair Cockburn ©Humans and Technology, Inc., 2000-2003 Slide 1

Agile Use Cases

( Writing Effective Use Casesmeets

Agile Software Development ! )

Alistair CockburnHumans and Technology

[email protected]://Alistair.Cockburn.us


Can use cases be agile? Yes(Can you be agile with use cases?) Yes

Do use cases contradict Agile ?: Use cases / not use cases / value of use cases vs stories: Agile / not agile / value of agile

When should we use agile use cases ?: document faster, later, cheaper, : plan on changing your mind along the way,: always.

Detecting and exercising available dimensions of freedom: Write less, more clearly (tips). : Shortcut process & use case structure ... (tips, tradeoffs): Tools

Q&A


Coming from agile non-use-cases to agile UCs is easier than coming from non-agile UCs

Overly complex use case writing is hard to change,tied to overly complex process (hard to change!)

Already understanding Agile means: already have a lighter process: already have mindset to simplify the writing: --> leads to agile use case writing.

Need to understand : (A) Simple use cases: (B) Agility as energy savings


Part 1:

What is / isn’ta

use case

(good for)


Good use casesare aren’t

TextNo GUI

No data formats3 - 9 steps in main scenario

Easy to readAt user’s goal level

Record of decisions made

UML use case diagramsdescribing the GUIdescribing data formatsmultiple-page main scenariocomplicated to readat program-feature leveltutorial on the domain

Use cases *can be* written --all up front --or-- just-in-time

each to completion --or-- in (usable) increments


Use case: Text describing scenarios of user succeeding or failing to achieve goal.

“Place an order” (User goal / Clerk)

Main scenario:1. Clerk identifies customer, item and quantity. 2. System accepts and queues the order.

Extensions:1a. Low credit & Customer is ‘Preferred’:

System gives them credit anyway.

1b. Low credit & not ‘Preferred’ customer: Clerk accepts only prepayment.

2a. Low on stock: Customer accepts rain-check:Clerk reduces order to available stock level.

(goal of primary actory) (level of goal [summary, user, subfunction])

(action steps: full sentences showing who takes the action! 3 - 9 steps long.)

(condition causing different actions)

(action step(s) handling those conditions)

(primary actor)

Robert Martin: “It shouldn’t take longer than 15 minutes to teach someone how to write a use case!”


Good use casesare aren’t

TextNo GUI





Use cases *can be* written --just-in-time --or-- all up front

in (usable) increments --or-- each to completion

(more Agile) (more common)


Use cases summarize end-user experience, not programmers tasks.

1980’s: Let’s write requirements in features!: User’s don’t understand...

...user pressure to write in use cases...

1990’s: Let’s write requirements in use cases!: Programmers’ work units are features, not use cases...

...programmer pressure to write in features...

2000: So let’s write requirements in features!: FDD & XP user stories...

...lose the end user experience again ...

A pendulum of features vs. use cases


1. Use cases hold functional requirements in an easy-to-read text format

2. They make a good framework for non-functional requirements & project scheduling.

3. Use cases show only the Functional req’ts.

4. Design is not done only in use case units.

Use cases have strong & weak points(as anything)


Use cases do not collect formulae, state, cardinality, performance, uptime, ...

Examples:1. Order cost = order item costs * 1.06 tax2. Promotions may not run longer than 6 months.3. Customers only become Preferred after 1 year.4. A customer has one and only one sales contact.5. Response time is less than 2 seconds.6. Uptime requirement is 99.8%.7. Number of simultaneous users will be 200 max.

Capture those in any form available,*somewhere* in your requirements files !


Goals make a good structure on which to hang requirements & project details.

Project planning capitalizes on goal structure:: Useable Releases.: Priorities, : Schedule, staffing

Name P. Actor Pr. Diff. ReleaseUpdate customer Customer high med 1Scan products Customer high high 1Generate invoice Finance high high 3Funds transfer Finance med high 4

(Note: spreadsheets are perfect for this!)


Use cases provide 4 values to the project at different times:

1. The list of goal names provides executives:: Shortest summary of what system will contribute: Project planning skeleton (priorities & timing)

2. The main success scenario provides all:: Agreement as to the system’s responsibilities

3. The extension conditions provide programmers:: List of things programmers have to watch for: List of things analysts have to investigate

4. The extension handling steps provide dev’t team:: Record of (tricky) business policy decisions


The hard parts about use cases is not typing,but thinking and agreeing.

• Total time: ~ 3 days construction : ~ 2 hours typing : 2-3/4 days spent thinking, arguing (over policy).

1. Is each step correct?2. Are there any system responsibilities between steps?3. Are there any outside systems this system should use?4. Are there any other stakeholders whose interests we

missed?5. Did we catch every extension condition?

(The programmers will (maybe))


Don’t try to teach a tutorial on the subject domain within the use cases!

In any text, receiver must always jump a gap.: Experts jump larger gaps: Novices jump smaller gaps.

To teach a domain, you need a textbook, not use cases.: Textbooks use smaller gaps.: Think of use cases as “documenting decisions”,

not “teaching the domain.”

Target the gap for the people: “sufficient” communication with a “small-enough”gap.: More experienced people need less writing !


Part 2:

What is / isn’tagile

development

(good for)


History: How did “agile” arise?

“Agile” techniques were in use since the beginning.

Agile (mobility-based) techniques did not show competitive advantage in the 1970s / 1980s,but did during the 1990s and do now.

1994: trials of semi-formal agile methodologiesRAD DSDM XP Crystal Scrum Adaptive

(3-1/2)


Development approaches are only attitudes, “centering of the attention”.

Declarations of core values declare an “attitude”

An attitude cannot promise success in the future,it can only be spoken successfully in the past tense. it is only a wish to be a certain way

A would-be agile processA would-be predictable processA would-be repeatable processA would-be inexpensive process

(4-1/2)


2001 Agile Software Development Manifesto - a declaration of values

“We are uncovering better ways of developing software by doing it and helping others do it.

Through this work we have come to value:: Individuals and interactions over Processes and Tools.: Working software over Comprehensive documentation.: Customer collaboration over Contract negotiation.: Responding to change over Following a plan.

That is, while there is value in the items on the right, we value the items on the left more.”

(Kent Beck, Mike Beedle, Arie van Bennekum, Alistair Cockburn,Ward Cunningham, Martin Fowler, James Grenning, Jim Highsmith,Andrew Hunt, Ron Jeffries, Jon Kern, Brian Marick, Robert Martin,Stephen J. Mellor, Ken Schwaber, Jeff Sutherland, Dave Thomas )


Agile development works because software development is an economic game

Economic consequences to each choice.: Less is usually better... “sufficient” is enough.

(Project success factors reviewed:)

Nourishment

Skills

CitizenshipCommunication

FocusIncrements

(Agility resides Here!)

(Includes developers AND users!)


Agile = shortcutting the process (cheating legally to win)

Scope

Time Resources

Process

(Some people use agile to handle late-breaking requirements changes, I use it to improve development efficiency)

Scope

Time Resources

The “iron triangle” isn’t a triangle at all --“Process” is the 4th dimension !


Agile development: short circuiting process steps without compromising final product.

• Focus on *early* & *frequent* delivery of *useful* software to real users using *just-in-time* techniques.

• Focus on *feedback* loops at all levels : (requirements design code test communication . . . )

• Replace fanfare around the process with people checking in with other people.

• *Talk* to users / sponsors, find out what they need!

• Adjust your working habits *monthly or quarterly* to fit your particular situation!


The Agile attitude focuses on:

1. Talent & Skill (fewer better people)2. Proximity (developers - developers - users)3. Communication (morale, daily standup)4. Just-in-time requirements and design5. Frequent Delivery (incremental development)6. Reflection7. Less paper, more tacit / verbal communication8. Tools9. Quality in work10. Different strategies for different projects


Agility *can*Be heavier or lighter, depending on circumstances

Use various requirements techniques (e.g., use cases, stories, features)

In agile development we valuefollowing the principles over following specific practices !

Good agile developmentis / does isn’t / doesn’t

EfficientLots of “just in time”

Adjust to circumstances(Re)Plan regularly

Lots of person-to-person comm.Adaptively cut fat in the process

hackingGiant Energy Up Front (GEUF)only XP (XP is one alternate)plan-lessPeople sitting in isolationrigid adherence


Is / Isn’t: Misconstruing the message

1. Agile SD is cheating

2. Agile SD requires the best developers

3. Agile SD is hacking

4. Agile SD won’t work for all projects


1. Agile techniques are “cheating”.

· Hire good people;· Seat them close together to help each other out;· Get them close to the customers and users;· Arrange for rapid feedback on decisions;· Let them find fast ways to document their work;· Cut out the bureaucracy.

This is: cheating stacking the decka good idea

the heart of agile software development


2. Agile only works with the best developers.

Every project needs at least one experienced and competent lead person. (Critical Success Factor)

Each experienced and competent person on the team permits the presence of 4-5 “average” or learning people.

With that skill mix, agile techniques have been shown to work many times.


3. Agile is hacking. (Hacker interpretations are inevitable.)

Hackers: “...spend all their time coding”Agilists: ...test according to project priorities,

recheck results with users often.

Hackers: “...talk to each other when they are stuck”Agilists: ...talk to each other and customers as

a matter of practice.

Hackers: “...avoid planning”Agilists: ...plan regularly

Hackers: “...management caves in out of fear”Agilists: ...expect management to provide priorities,

& participate jointly project adjustments.


4. Agile won’t work for all projects.

Right. (Business isn’t fair).

Agile is an attitude prioritizing: Project evaluation based on delivered code Rapid feedbackPeople as a value center Creativity in overcoming obstacles

Not every team ... values the Agile value set.... can set up the needed trust and communication

(5-6/6)


Problem Size

Light methodology

Heavymethodology

# people needed

Lighter-agile vs. Heavier-agile :Light is good, but has limits

fewer people

more people


Number of people involved

C

riti

cali

ty(d

efec

ts c

ause

loss

of.

..)

Comfort(C)

Essentialmoney

(E)

Life(L)

+20%

. . . Prioritized for Legal Liability

1 - 6 - 20 - 40 - 100 - 200 - 500 - 1,000

C6 C20 C40 C100 C200 C500 C1000

D6 D20 D40 D100 D200 D500 D1000

E6 E20 E40 E100 E200 E500 E1000

L6 L20 L40 L100 L200 L500 L1000

Prioritized for Productivity & Tolerance

Discretionarymoney

(D)

Suit the process to the occasion project size & priorities, system criticality


Group’s tolerance for ambiguity / uncertainty

Pro

du

ctiv

ity:

(F

lux

& U

nce

rtai

nty

)Reality Check: Work as parallel & light as project features and personalites permit.

e-projects

old-schoolprojects

Project requires at least this muchproductivity to succeed

Where is your group,your projecton this graph??


Part 3:

Agile-ly generatingagile use cases


Core elements to using use cases *agile-ly* increments, just-in-time, close communication

• Write just enough use case content to plan to the needed planning horizon: Long (project) horizon -> just use case names or briefs.: Short (iteration) horizon -> extension handling.

• Just barely beat the programmers to the extension handling decisions (just in time)

• Write just enough content for the team to understand.

• *Show* UCs, system to users/sponsors, get feedback!

• Adjust your working habits *each iteration* to fit your particular situation!


Core elements to using use cases *agile-ly*:increments, just-in-time, close communication

Ask, • How much do we need to write at this time?• When do we need to write more?• What is the fastest way to write/convey them?• Who benefits from more information or more detail?


Take advantage of available degrees of freedom in the process

1. Write less more clearly (always)

2. Write less (sometimes)

3. Shortcut the use case structure (sometimes)

4. Write later & shortcut the process (usually)


1. Write less more clearly (always)

TextNo GUI





(shorter, more economic& more readable!)


2. Write less (sometimes)(the economics of communication)

• Fully dressed use cases• Casual use cases• Use case briefs

The correct form to use depends on your project’s priorities and properties !


Economics of communication: Fully Dressed (expensive, complete)

Use Case 12. Buy stocks over the web Primary Actor: Purchaser (user) Scope: PAF

Level: user goal Precondition: User already has PAF open.

Guarantees: sufficient log information exists that PAF can detect what went wrong.

Success Guarantees: remote web site acknowledged purchase, user's portfolio updated.

Main success scenario:

1. User selects to buy stocks over the web.

2. PAF gets name of web site to use (E*Trade, Schwabb, etc.)

3. PAF opens web connection to the site, retaining control.

4. User browses and buys stock from the web site.

5. PAF intercepts responses from the web site, and updates the user's portfolio.

6. PAF shows the user the new portfolio standing.

Extensions:

2a. User wants a web site PAF does not support:

2a1. System gets new suggestion from user, with option to cancel use case.

3a. ...


Economics of communication: Casual (less expensive, less complete)

Buy something (Purchaser / user-goal level)

The Requestor initiates a request and sends it to her or his Approver, who completes the request for submission and sends it to the Buyer. The Buyer finds the best vendor, initiates PO with Vendor.

At any time prior to receiving goods, Requestor can change or cancel the request. Canceling it removes it from any active

processing.


Economics of communication: Brief (inexpensive, just a short note)

Actor Goal Brief Description

Production Staff

Preparedigitalcartographicsource

Convert external digital data to standard format, validate & correct in preparation for merging with operational database.

... ... ...

... ... ...

(Note: spreadsheets again!)


3. Shortcut the use case structure (sometimes)

Use cases are not read by a compiler but by a human...--> so,

Don’t be rule-bound, but adapt the form to your needs.


Test department needs detailed requirements.Development can usually use agile ones.

Use cases

Dataformats

UI descr.

Program

Tests

Domainexpert

Usage expert R D

R D

(Detailed, expensive, long, tedious, brittle use cases)

(Shorter, cheaper, easier to read, more stable (agile) use cases)

(Test department)

R D

[Alistair’s generic process model]

(Development department)


4. Write later and shortcut the process (usually)

Use cases *can be* written --just-in-time --or-- all up front

in (usable) increments --or-- each to completion

(more Agile) (more common)

Req'ts

Design

Validate syntax

Validate req'ts

Code

Validate logic

Use the “Validation V” view of increments


Project horizon -> all use case briefs or casualIteration horizon -> full use case, just-in-time

Full Project

S S

S

E E E E E E

Iteration Iteration Iteration

(all UCs, ultra-light content, estimation purposes)

(just-in-time, complete) (just-in-time, complete) (just-in-time, complete)

(10 use cases) (10 more use cases) (10 more use cases)


Finally, Tools: Choose for the value it delivers, not for its popularity

• List of UCs for project planning & status:: Spreadsheets are very effective: Lotus Notes medium effective

• Main success scenario for agreement:: Flipcharts in meeting good for fast disagreement: Word processor (Lotus Notes) quite effective

• List of extension conditions for completeness:: Word processor quite effective: Flipcharts in project room? (untried)

• Extension handling steps for policies:: Word processor very effective: WikiWiki technology? (http://c2.com)


Summary of Agile Use Cases

• User’s goal level - Text - 3-9-step main scenario - No GUI - No data formats - Easy to read -Record of decisions made (not a tutorial)

• Write briefs and casuals to estimate & plan projectWrite full use cases just-in-time per iteration

• Just-in-time = extension-handling decisions made before the programmer gets around to asking for them.

• Spreadsheets good for briefs, planning activities.Focus on communicating, not filling templates


(1) In 10 minutes: Write a use case for a clerk entering a video rental into the computer.

( Write the basic dialog between the clerk and the system, Name all the things that could go wrong during the procedure. )


(2) In 10 minutes: Name all the use cases for a video rental store computer system.

( List every person who will use the computer system.For each person, list every reason they have to use the system. )


(3) In 5 minutes: Prioritize the list of UCs(order in which to develop & deliver them).

( Rank for when it is *really* needed, by dependency or business payback. )


Agile Use Cases

Alistair CockburnHumans and Technology

[email protected]

http://Alistair.Cockburn.us

Alistair Cockburn©Humans and Technology, Inc., 2000-2003 Slide 1 Agile Use Cases ( Writing...

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