.Net Software Architects UG Meeting Methodology for Use case development Arnon Rotem-Gal-Oz Product Line Architect [email protected].

.Net Software Architects .Net Software Architects UG MeetingUG Meeting

Methodology for Use case development

Arnon Rotem-Gal-OzProduct Line [email protected]

The king’s Ship Wasa - 1628The king’s Ship Wasa - 1628

No Architecture description Changes done on the fly,

often under market/customer pressure

Testing ignored Didn’t know how to tell the

clients No The system last longer than

was ever imagined Maintenance costs far exceed

ordinary development No Specification !

AgendaAgenda

VocabularyWhy Use Cases?Why should we care?The challenges of UC modeling in large

projectsThe Methodology Summary

VocabularyVocabulary

Actor – Role(s) external parties that interact with the system

Use Case – A sequence of actions that the system performs that yields an observable result of value to an actor. [Booch 1999]

Use Case Model - Bag that contains – Actors list, packages, diagrams, use cases, views

Use Cases benefitsUse Cases benefits

Promote customer involvement

Help manage complexity– Layers– Focus on real user needs

Groundwork for user manual, test cases

Help us work in iterations

Use cases aren’t everythingUse cases aren’t everything

Non-behavioral requirements– Performance– Design constrains– Etc.

Sometimes – an overkill

Use cases & Architects ?!Use cases & Architects ?!

Requirements drive the design !!!

Help force designers focus on concrete issues

Help identifying technical and business risks

Can be used to help validate the architecture

Use cases & Architects ?! (cont.)Use cases & Architects ?! (cont.)

Architects should be involved in (if not responsible for) - UC prioritization !

Architectural design workflow (Kruchten 2003):– Select scenarios : criticality and risk– Identify main classes/components and their responsibility– Distribute behavior– Structure into subsystems, layers and define interfaces– Define distribution and concurrency– Implement architectural prototype– Derive tests from use cases– Evaluate architecture

Overview Overview

Use case modeling for large projects is problematic

Most literature is lacking (too simplistic / not practical)A practical reasonable process is needed!

priorities

Team

Validate

UC Verify

Refactor

PDOM

VisionDiagram

Naïve approachNaïve approach

Find Actors

Find Use Cases

Describe Use Cases

ChallengesChallenges Model

– Duplicates– Explosion– Making sure the requirements are good

Team – Efficiency– Fragmentation

Process– Details too early– Quitting Time– Waterfall

The MethodologyThe Methodology

To resolve the challenges we need a process that is: – Ordered– Controlled– Not too complicated– Not too demanding– Flexible

Methodology – Initialization StepsMethodology – Initialization Steps

Define System BoundaryOrganize the TeamBuild a Problem Domain Object Model

Methodology - ProcessMethodology - Process

Find ActorsFind Use CasesOrganize the ModelPrioritize Use CasesDescribe Use CasesRefactor the Model

Methodology – Supporting StepsMethodology – Supporting Steps

Verify and ValidateAdd Future Requierments

Methodology – End GameMethodology – End Game

Knowing when to stop !

Step 1: Define System BoundaryStep 1: Define System Boundary

Vision and Scope– What problems are solved– Who are the stakeholders– Client’s Organization main goals– System main goals– Boundaries of the solution– Future Directions

Step 2: Organize the TeamStep 2: Organize the Team

Small teamsHeterogeneous Multi-tier reviewsRequirements manager

Step 3: Build a PDOMStep 3: Build a PDOM

Terms and relationsIterative development

Police Car

Watch

Policeman

Work in

Beat

Beat Car

Is aAllocated to

Beat Team

AreAllocated to

Drive

Police HQ

Watch Commander

Is a

Commands

Emergency CenterDistrict

Commands

Commands Has an

Rapid Response Car

Is a

Sector

Is made of

Is made of

Allocated to

Step 4: Find ActorsStep 4: Find Actors

Identify– Ask the End-Users– Documentation

Issues– Roles Vs. Job Titles– The Clock

Actor HierarchyActor Hierarchy

Emergency Center Supervisor

User

Watch Commander

Emergency Center Operator

HQ Watch Commander

Cop

User

(from Actors)

Log in

Step 5: Find Use CasesStep 5: Find Use Cases

Scenario Driven– Find measurable value– Business events– Services actor needs / supplies– Information needed– Recurring

Actor/Responsibility Unstructured aggregation Mission decomposition

Misuse cases

Step 5: Find Use Cases ../2Step 5: Find Use Cases ../2

Initial Description– Unique ID– Scope– Pre conditions– Success Guarantee– Trigger

Example : Initial descriptionExample : Initial descriptionUse Case: Run Special Op.

ID: UC4

Scope: The Watch Commander chooses a Special operation to manage.The task team chosen for the operation is briefedThe watch commander then monitors the operation as it unfolds (sending out orders as needed)The task team is debriefed for the results and a final report is made.

Primary Actor: Watch Commander

Preconditions: A Special Op. Plan is saved in the system.

Success Guarantees: The Special Op. recordings (Forces movement, Voice recordings etc.) are saved in the system. The operation's statistics are saved in the system. Operation Final Report is saved and printed.

Trigger: The Watch Commander chooses a Special Op.

Step 6: Organize the ModelStep 6: Organize the Model

Ever Unfolding storyCategory sets

– Status, scope, stakeholders, sub-systemsSubject Category hierarchyViews

– Architectural view (i.e. SAD - Use Case View)

Step 7: Prioritize Use CasesStep 7: Prioritize Use Cases

Risk Classes– Business Risks– Architectural Risks– Logistical Risks

Iterative development– Small vs. Large projects

Step 8: Describe Use CasesStep 8: Describe Use Cases Template

– Main success Scenario– Variations– Exception– Assumptions– Status– Priority– Stakeholders and concerns– Issues– Non-behavioral reqs.– Extension points.

Step 8 : Describe Use Cases ../2Step 8 : Describe Use Cases ../2

Focus

Technology neutral

Activity diagrams

Step 9: Refactor the ModelStep 9: Refactor the Model

Relations– Trace (decomposition)– Include (common sub-behavior)– Extend (promoted alternatives)– Generalize

Merge droplets

Step 10: Verify & ValidateStep 10: Verify & Validate

Verification – Making sure we build the product right

Validation – Making sure we build the right product

Traceability Inspection Reviews Walkthroughs Prototypes

Step 10 : V&V ../2Step 10 : V&V ../2

Actors– Are all the actors abstractions of specific

roles?– Are all the actors clearly described, and do

you agree with the descriptions? – Is it clear which actors are involved in which

use cases, and can this be clearly seen from the use case diagram and textual descriptions

Step 10: V&V ../3Step 10: V&V ../3

Use Cases– Does the use case make sense? – For each iteration: Are all the use cases described at

the same level of detail?– Are there any superfluous use cases, that is, use cases

that are outside the boundary of the system, do not lead to the fulfillment of a goal for an actor or duplicate functionality described in other use cases?

– Do all the use cases lead to the fulfillment of exactly one goal for an actor, and is it clear from the use case name what is the goal

Step 10: V&V ../4Step 10: V&V ../4 The Scenarios

– Are there any variants to the normal flow of events that have not been identified in the use cases, that is, are there any missing variations? (“happy days scenarios”, exceptions, variation, “soup-opera scenarios”)

– Are the triggers, starting conditions, for each use case described at the correct level of detail?

– Does the behavior of a use case conflict with the behavior of other use cases?

– Is the number of steps in the complex scenarios excessive (12 to 15 is getting borderline)?

Step 10: V&V ../5Step 10: V&V ../5

Organization & Prioritization– Are all the use cases organized in an

appropriate manner (e.g. by functional area, by dependency, by actor etc)?

– Are all the use cases within a package consistent with the theme of the package?

– Is the priority mechanism documented?– Are the use cases prioritized correctly?

Step 11: Add Future RequirementsStep 11: Add Future Requirements

Capture Change cases– Preparing for change– Impact analysis

Example: Future RequiermentsExample: Future Requierments

Step 12: Knowing When to StopStep 12: Knowing When to Stop

Project Level– Complete list of actors and goals– Customer approval– Design ready

Iteration Level– Covered all currently prioritized use cases– Level of detail

SummarySummary

What we have seen…

Additional Issues– Project Management– Requirements Management– Configuration Management

Further Reading…Further Reading…

Writing Effective Use Cases (Cockburn)Patterns for Effective Use Cases (Adolph

& Bramble)Advanced Use Case Modeling (Armour &

Miller)

The End…The End…

Questions/Full Article?Questions/Full [email protected]@cool.as

CHAOS Chronicles III - Jan. 2003CHAOS Chronicles III - Jan. 2003 Success FactorsSuccess Factors

Executive-management supportUser involvement Clear business objectivesMinimizing scope

– Time is the enemy of all projects– Scope equals time

Firm basic requirements– Balance between "Paralysis through Analysis"

and what happens if requirements are not specified

“CHAOS research isdedicated to solving the mystery of project success and failure”

http://standishgroup.comhttp://standishgroup.com

Example: Finding Use CasesExample: Finding Use Cases What measurable value is needed by the actor?

– Plan Special Op.– Monitor Special Op.– Analyze Crime Patterns.

What business event might this actor initiate (based on her role)? – Handle Emergency Call– Call Car for Service

What services does the actor need from the system?– Find Navigation Route– Get Unit Status– Map Incidents

What services does the actor provide?– Dispatch Units– Issue Tickets

What information does the actor need from the system?– Get Car Registration History– List Duties

What are the activities that are recurring and triggered by time?– Get Updated Situation Awareness Map– Generate Emergency Center Statistics Report– Generate Crime Trends Report.

Example : Mis-Use CasesExample : Mis-Use Cases

User

(from Actors)

Log in

Tap Communications

Hacker

(from Mis-Actors)

Obtain Password

<<include>>

<<include>>

User

(from Actors)

Log in

Tap Communications

Hacker

(from Mis-Actors)

Obtain Password

<<include>>

Enforce Password Regime

Sys Admin

(from Actors)Monitor System

<<detect>>

<<detect>>

<<mitigate>>

<<include>>

Example : Use CaseExample : Use Case

Use Case: Handle Emergency Call

ID: UC24

Scope: The Operator accepts an incoming call, enters the incident information and dispatch a unit to the location of the incident

Stakeholders and Concerns: Victim - wants the police to arrive as soon as possible Beat Team – don't want to be dispatched to handle false incidents.

Primary Actor: Emergency Center Operator

Preconditions: Operator logged in.

Success Guarantees: The Call has been recorded A unit has been dispatch to investigate the incident The incident details are saved in the system

Trigger: A Citizen's incoming call has been directed by the Call Center system to an Operator.

Example : Use Case ../2Example : Use Case ../2Main Success Scenario:1.The system begins recording the call.2.The system traces the caller address.3.The Operator takes the incidents location4.The system calculates available police units.5.The Operator takes the incidents detail6.The system presents a list of available teams and their distance from the incidents estimated location.7.The Operator chooses a unit to handle the incident8.The system dispatches the incident details to the chosen team.9.The Operator takes the caller details10.The system saves the incidents details including call statistics11.The system ends recording.

Variations:1.step 2 - when the caller uses a mobile phone

a. Locate the callers current location2.step 2 - when the caller is on the black list (known to call for no reason)

a.The Operator is presented with additional questions to ask the callerb.The system marks the incident as low-priority on count of possible false alarm.

3.step 7 - when the incident does not require police intervention.a.The Operator closes the incidentb.The system saves the termination reasons and continues from step 10

4.step 7 - if the incident requires a fire truck/ambulancea. The Operator chooses which authority to notify (fire / ambulance etc)b.The system dispatches the incident details to the appropriate authority's system

Example: Use Case ../3Example: Use Case ../3Main Success Scenario:1. The system begins recording the call.2. The system traces the caller address.3. The Operator takes the incidents location4. The system calculates available police units.5. The Operator takes the incidents detail6. The system presents a list of available teams and their distance from the incidents estimated location.7. The Operator chooses a unit to handle the incident8. The system dispatches the incident details to the chosen team.9. The Operator takes the caller details10. The system saves the incidents details including call statistics11. The system ends recording.

Exceptions: 1.step 2 - when the call cannot be traced

a.The system suggests lowering the priority of the call on the count of an unknown callerb.The operator decides what priority to allocate for the incident.

2.step 6 – when there is no available free forcea.The system presents the operator with low-priority incidents (along with the reason for low-priority

3.step 8 – communication problem with the unit dispatcheda.The system performs step 6 and 7 again.

4.step 8 – communication problem with all the units.a.The system presents the operator the incidents details to allow dispatching by radio/mobile phone.

Non Behavioral Requirements: The system should present as few screen as possible to the operator Locating a free unit should take less than 30secondsCommunications to and from the unit should be secure (encrypted) to prevent eavesdropping by offenders/media

Example: Use Case LevelsExample: Use Case Levels

Service Cars

(from Service/Maintenance management)

Fix Car After Accident

(from Service/Maintenance management)

Maintain Police Cars

(from Service/Maintenance management)

Track Police Cars Usage

(from Service/Maintenance management)

<<trace>>

<<trace>>

<<trace>> Why ?How ?

Example : Refactoring Example : Refactoring Common Sub-behavior Common Sub-behavior

Find Navigation Route

(from Navigation)

Respond to Incident

(from Incidents Response)

Beat Cop

(from Actors)

Perform Assignment

(from Special Ops support)

<<include>>

<<include>>

Use Case ViewUse Case View

Concerns– What’s the conceptual framework in which the system

operates– What are the key processes and events that must be

presented in the system– Why the architecture is the way it is

Stakeholders– Users– Designers & Developers

Integrate the other views