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Requirements Engineering

Nupul Kukreja,Barry Boehm

9th September 2013

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Agenda• Part 1– Pervasiveness of Software– Motivation for Requirements Engineering– Interrelationships: Requirements Engineering, Enterprise &

Software Development– Types of Requirements– Goals of Requirements Engineering– Framework for Requirements Engineering

• Part 2– Requirements Practice in 577– System and Software Requirements Document– User Stories– Documenting Requirements in 577

Team Mixer after class in

Engineering Quad (outside OHE)

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Pervasiveness of Software• Software-intensive systems prevalent across

industries/domains – E.g.: automotive, finance, consumer electronics, medical devices etc.,

• Information systems: – Collects, stores, transforms, transmits, and/or processes information

or data– Goal: Provide information at right place/time– Ex.: Accounting system

• Embedded software-intensive systems:– Software only ONE (important) part of overall system– Often closely integrated with hardware– Ex.: Anti-lock braking system of a car

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Challenges in Software Development• Software-based innovations

– Customers demanding innovative features software is key for realizing innovation

• Increasing Complexity– Greater number of functions realized by software increasing complexity

i.e., increased integration with external systems, customizability etc.,• Higher quality demands

– Pervasiveness of software higher level of quality• Shorter development times

– Increasing competition faster time to market• Pressure to reduce costs

– Increasing market pressure software systems must be developed at lower costs

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Project Success Rate

2000 2002 2004 2006 20080

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20

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50

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4951

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4644

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1518 19

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3532

2010 Standish Group CHAOS Summary Report

ChallengedFailedSucceded

Challenged: Over budget/schedule or undelivered projectsFailed: Cancelled projects

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Lack of Stakeholder involvement and convergence viewed as major causes of project failure

1. User Involvement2. Executive Support3. Clear Business Objectives4. Emotional Maturity5. Scope Optimization6. Agile Process7. Project Management Expertise8. Skilled Resources9. Execution Capability10.Tools and Infrastructure

CHAOS ’10 – Factors Influencing Project Success

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2 Minutes

In-class• Create a means for protecting a small group of

human beings from the hostile elements of their environment– List or draw or describe the “creation” in a couple

of lines• Note down questions you may have

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Why Is RE Important?• Flawed requirements a major cause of project

failure • Fixing an error in later phases 10x more expensive• Incorrect requirements ↔ Incorrect system leads

to wasted costs• System maybe unreliable for practical use

disrupting normal day-to-day operations• The primary vehicle for going from “vision” to

“realization”

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RE and the Enterprise

Requirements Engineering

Marketing

Customer Relationship Management

Product Management

Product roadmap/ strategy, key

requirements

New and revised

requirements

Customer wishes, Reported problems

Realized changes and

enhancements

Market needs and trends,Price range

New Features

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RE and Software Development

Requirements Engineering

Project Management

System Maintenance

Quality Assurance

Requests for clarification and

improvement

Requirement Artifacts Change requests

Status of change requests

Project plan, Approved goals

Requirements & constraints Design &

Development

Solutions, New technologies

Monitoring data, Elicited goals

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Defining “Requirement”IEEE 610.12-1990:1. A condition or capability needed by a user to

solve a problem or achieve an objective2. A condition or capability that must be met or

possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed documents

3. A documented representation of a condition or capability as in (1) or (2)

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Types of Requirements• Functional Requirements: specify the functionality the system shall

provide to its users– Ex.: The system shall allow the users to access their profile page after they

provide valid credentials• Quality Requirements (a.k.a., Levels of Service): define the quality

properties of the entire system or of a system component, service or function– Ex.: Reliability, performance under high loads etc.,– “-ilities”: Availability, flexibility, scalability, usability, robustness,

interoperability etc.,• Constraints: Organization or technological requirement that

restricts a way in which the system shall be developed– Ex.: Legal constraints (Sarbanes-Oxley), Project/Budget/ Schedule

constraints, Physical constraints etc.,

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Goal of RE: Establishing a Vision in Context

• Requirements Engineering processes start with an aim to change current reality

• Vision: (a.k.a “system vision”)– Essence of desired change defined briefly and

precisely– Describes overall goal(s) of the system– Usually associated with particular point in time of

when the vision should be realized– Serves as a guide during development for all Success

Critical Stakeholders (SCS) involved in the project

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Goal of RE: Establishing a Vision in Context

• Each system is embedded within a given context

• Context (a.k.a. “system context”): Part of the system environment relevant for– Defining, understanding & interpreting system

requirements

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Visualizing “Vision” in “Context”

Vision defines focus

• Establish system vision within existing system context• Deal with parts of the real world that are relevant

and their relation to the development context

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Framework For RE

System Context

Core Activities

Requirements Artifacts

Valid

ation

Man

agem

ent

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Framework For RE

System Context

Subject FacetMaintain

information about objects/events in

the real world.

Usage Facet Desired workflows,

usage goals, different user

groups, interaction models, laws & standards etc.,

IT System FacetExisting hardware,

software, communication

networks, peripheral devices

etc.,

Development FacetProcess guidelines

and constraints, QA methods, maturity

models, development

environments etc.,

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Relationship Between Facets

Subject Facet

Representation

PresentationApplication

Usage Facet Development Facet

IT System Facet

RE happens here!!

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Three Dimensions & Goals of Requirements Engineering

• Content:All relevant requirements are explicitly known and understood at the required level of detail

• Agreement:A sufficient agreement about the system requirements is achieved between the success critical stakeholders

• Documentation:All requirements are documented and specified in compliance with the relevant documentation/specification formats & rules

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Visualizing The “Three Dimensions” Content

Documentation

Agreement

complete

vague

informal compliant with rules

individual views

consolidated views

Goal

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Framework For RE

Core Activities

Documentation Document & specify elicited requirements as per defined

documentation and specification rules. Also

capture rationale and other relevant information

Elicitation

Negotiation1.Detect conflicts and make them explicit2. Resolve identified conflicts

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Framework For RE

Elicitation

Identifying Requirement Sources

StakeholdersExisting Documentation

Existing System(s)Elicit Existing Requirements

Elicit already “known” requirements from relevant

sources

Developing new & innovative requirements

Typically not elicit-able and require collaborative and

creative processes

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Techniques For Elicitation• Interviews• Workshops• Focus Groups• Observation of stakeholders/users etc.,• Questionnaires • Perspective-based readingUsually supported by “Assistance Techniques”– Brainstorming– Prototyping– Mind Mapping– KJ Analysis/Method– Elicitation Checklists

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Framework For RE

Goals Stakeholder intention with

regard to the objectives, properties or use of the

system

ScenariosPositive/Negative,

Misuse,Exploratory,

Current-state/desired state,Main, alternative or exception

Solution oriented requirementsData Model,

Functional Model,Behavioral Model

Requirements Artifacts(Documented Requirements)

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Framework For RE• Validation of context consideration

Check whether all relevant aspects in 4 contexts have been elicited, documented within the RE process

• Validation of execution of activitiesCheck adherence of activities to process, standards, guidelines etc.

• Validation of requirement artifactsCheck documented requirements w.r.t. content, documentation and agreements

Valid

ation

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Validation Techniques• Inspections• Walkthroughs• Desk-checking (checking programs with

pen-paper)• PrototypingAbove are usually assisted by:• Validation checklists• Perspective-based reading• Verbalization of models• Creation of artifacts

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Framework For RE• Observation of system context

Identification and management of context changes• Management of RE activities

Monitoring, controlling and adjustment of planned workflow of elicitation, documentation, negotiation and validation activities – standard project management

• Management of requirements artifacts– Establishing traceability between different artifacts– Prioritizing requirements– Managing changes via change management processes

Man

agem

ent

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RE Framework == VBSE 4+1

• RE Framework advocated by Klaus Pohl is, in essence, isomorphic to VBSE’s 4+1

• VBSE brings value considerations to the foreground; RE Framework doesn’t seem to make it explicit

• Each of the ‘steps’ of the RE framework is traceable in VBSE’s 4+1 structure (and vice versa)

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Part 2

Requirements Practices in 577ab

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Requirements Capturing in 577• Previously captured in System and Software Requirements Document (SSRD)• Capability requirements (both nominal and off-nominal): i.e., the fundamental

subject matter of the system, measured by concrete means like data values, decision-making logic and algorithms.

• Level of Service Requirements (sometimes referred to as Non-functional requirements): i.e., the behavioral properties that the specified functions must have, such as performance, usability, etc.

• Global constraints: requirements and constraints that apply to the system as a whole e.g.: Interface Requirements, Budget and Schedule Requirements, Implementation Requirements, and other Project Requirements

• Evolution Requirements: not included in initial delivery, but need to be supported by the System’s Architecture

• Priorities on how the system must be implemented : MoSCoW( Must Have, Should Have, Could Have, Want to Have)

• Commitment: addressing WinWin agreements, policies, constraints

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Main Kinds of Requirements• Product Requirements

– Capability Requirements• local to system, specific system functionality

– Level of Service Requirements• local to system, may affect many system requirements

• System Interface Requirements– Varies; affects groups system requirements

• Project Requirements– Global to project, affects overall system requirements

• Evolutionary Requirements– Varies; effects design and implementation– Necessary to future proof the system

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Example of Capability RequirementRequirement: CR-13

Description:The Archive user subsystem allows the user to view the list of archive items, select the item of interest, deselect if required and view the overview on the selected archive items.

Priority: Must Have

Input(s): - Selected archive items- The database with the overviews of the archive items.

Source(s): User InputOutput(s): Overview display of the archive items.

Destination(s): User Display

Pre-condition(s): The user has performed a search by keyword or has browsed the archive.

Post-condition(s): The user either makes an advance request or starts another search or exits fromthe system.

WinWin Agreements: [Agreement 1]

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Levels of ServiceQuality attributes of the system:• Dependability– Reliability– Availability

• Usability– Ease of learning– Ease of use

• Performance• Maintainability• Portability• Interoperability• Reusability

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Poor Examples of LOS

• M: The system should be as fast as possible

• R: The system should be available 24/ 7 (even if organization does not support activities beyond day time)

• S: The system shall be implemented as per the standards laid out by USC

• A: The system shall be available 100% of the time (for an unreliable network- based system)

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SSRD in Practice

In 2D

The true 3D view

Too much detail and too much

to capture

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Change Management & SSRD?

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Along came a

User Stories

SSRD

Story

What we thought… What was actually intended…

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The User Story – 3Cs

Lightweight Ecstasy

Card

A promissory note of intent

Conversation

Discussion & clarification of intent (a.k.a requirement)

Confirmation

Acceptance Tests

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User Stories• Written on small index cards• Usually of the form:

As a <role>, I can <activity> so that <business value>

Ex.: As a Consumer I want to be able to see my daily energy usage so that I can lower my energy costs and usage

• Lacks details captured by traditional requirements specifications

• Details conveyed primarily through conversations• Formalized via acceptance tests

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INVEST-ing in User Stories

I = IndependentN = NegotiableV = ValuableE = EstimableS = SmallT = Testable

Commonly used acronym in the Agile World to describe attributes of a good user story:

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Theory-WCustomer

Developer

STOP THIS MADNESS!

Think of requirements as stakeholder negotiated win

conditions!!

As a team discuss what will make each of you “win”

(a.k.a. win conditions)

Identify any issues and come up with options to resolve them

Reach a mutual consensus and move

forward (WinWin Equilibrium)

Dr. Boehm

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WinbookTheory - W

Requirement Specifications

Putting It All Together

User Stories

Facebook Gmail

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Winbook• A collaborative, social networking based tool

for requirements brainstorming similar to facebook…

• …with requirements organization using color-coded labels similar to Gmail…

• …to collaboratively converge on software system requirements reaching win-win equilibrium (based on Theory-W)…

• …by keeping it short and simple like XP’s user stories!

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Requirements in 577• Requirements are treated as “Win Conditions”• Win Conditions are captured in Winbook• Win Conditions subsume user stories:– Capability/Functional Requirements/Win Conditions

can be conveniently phrased as user stories• Win Conditions are negotiated within Winbook

itself• Win Conditions are linked to corresponding use-

cases facilitating “downstream value traceability”

Challenges in RE• Things that can (and do) make life difficult– Missing Requirements– Ambiguous Requirements (major problem)– Changing Requirements (changes in technology,

marketplace, political & legal changes, economic changes etc.,)

– Non-identified Stakeholders– Location/Time differences and communication overhead– IKIWISI (I’ll know it when I’ll see it)– Implicit Assumptions

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Key Takeaways• Requirements are very critical to the field of Software

Engineering• Almost everything documented information is a form of

requirement• No single artifact to rule them all – content usually split

across various artifacts• Very cooperative and iterative• Assumptions/Conflicts must be made explicit and

validated/resolved• SSRD is more commonly found in the wild• 577 uses Winbook for documenting ‘requirements’ making

the process ‘fun and lightweight’

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References• Requirements Engineering: Fundamentals,

Principles and Techniques – Klaus Pohl• Agile Software Requirements – Dean

Leffingwell• Exploring Requirements: Quality Before

Design – Gause & Weinberg• User Stories Applied – Mike Cohn• Software Engineering Economics – Barry

Boehm62