Slide 1 Requirements Engineering Processes. Slide 2 Something to Think About … The indispensable first step to getting the things you want out of life:

Slide 1

Requirements Engineering Processes

Slide 2

Something to Think About …

The indispensable first step to getting the things you want out of life: decide what you want.

—Ben Stein

Slide 3

Objectives

To describe the principal requirements engineering activities and their relationships

To introduce techniques for requirements elicitation and analysis

To describe requirements validation and the role of requirements reviews

Slide 4

Requirements engineering processes

The processes used for RE vary widely depending on the application domain, the people involved and the organisation developing the requirements.

However, there are a number of generic activities common to all processes• Requirements elicitation;• Requirements analysis;• Requirements validation;• Requirements management.

Slide 5

Feasibility studies

A feasibility study decides whether or not the proposed system is worthwhile.

A short focused study that checks• If the system contributes to organisational

objectives;• If the system can be engineered using current

technology and within budget;• If the system can be integrated with other

systems that are used.

Slide 6

Feasibility study implementation

Based on information assessment (what is required), information collection and report writing.

Questions for people in the organisation• What if the system wasn’t implemented?• What are current process problems?• How will the proposed system help?• What will be the integration problems?• Is new technology needed? What skills?• What facilities must be supported by the proposed

system?

Slide 7

Elicitation and analysis

Sometimes called requirements elicitation or requirements discovery.

Involves technical staff working with customers to find out about the application domain, the services that the system should provide and the system’s operational constraints.

May involve end-users, managers, engineers involved in maintenance, domain experts, trade unions, etc. These are called stakeholders.

Slide 8

Problems of requirements analysis

Stakeholders don’t know what they really want. Stakeholders express requirements in their own

terms. Different stakeholders may have conflicting

requirements. Organisational and political factors may influence the

system requirements. The requirements change during the analysis

process. New stakeholders may emerge and the business environment change.

Slide 9

Process activities

Requirements discovery• Interacting with stakeholders to discover their

requirements. Domain requirements are also discovered at this stage.

Requirements classification and organisation• Groups related requirements and organises them into

coherent clusters. Prioritisation and negotiation

• Prioritising requirements and resolving requirements conflicts.

Requirements documentation• Requirements are documented and input into the next

round of the spiral.

Slide 10

Requirements discovery

The process of gathering information about the proposed and existing systems and distilling the user and system requirements from this information.

Sources of information include documentation, system stakeholders and the specifications of similar systems.

Slide 11

ATM stakeholders

Bank customers Representatives of other banks Bank managers Counter staff Database administrators Security managers Marketing department Hardware and software maintenance engineers Banking regulators

Slide 12

Viewpoints

Viewpoints are a way of structuring the requirements to represent the perspectives of different stakeholders. Stakeholders may be classified under different viewpoints.

This multi-perspective analysis is important as there is no single correct way to analyse system requirements.

Slide 13

Types of viewpoint

Interactor viewpoints• People or other systems that interact directly with the

system. In an ATM, the customer’s and the account database are interactor VPs.

Indirect viewpoints• Stakeholders who do not use the system themselves but

who influence the requirements. In an ATM, management and security staff are indirect viewpoints.

Domain viewpoints• Domain characteristics and constraints that influence the

requirements. In an ATM, an example would be standards for inter-bank communications.

Slide 14

Viewpoint identification

Identify viewpoints using• Providers and receivers of system services;• Systems that interact directly with the system

being specified;• Regulations and standards;• Sources of business and non-functional

requirements.• Engineers who have to develop and maintain

the system;• Marketing and other business viewpoints.

Slide 15

LIBSYS viewpoint hierarchy

Articleproviders

FinanceLibrarymanager

Librarystaff

Users

InteractorIndirect

All VPs

Classificationsystem

UIstandards

Domain

ExternalStaffStudents CataloguersSystem

managers

Slide 16

Interviewing

In formal or informal interviewing, the RE team puts questions to stakeholders about the system that they use and the system to be developed.

There are two types of interview• Closed interviews where a pre-defined set of

questions are answered.• Open interviews where there is no pre-defined

agenda and a range of issues are explored with stakeholders.

Slide 17

Interviews in practice

Normally a mix of closed and open-ended interviewing.

Interviews are good for getting an overall understanding of what stakeholders do and how they might interact with the system.

Several issues need to be addressed before conducting interviews for understanding domain requirements • Requirements engineers cannot understand specific

domain terminology;• Some domain knowledge is so familiar that people find it

hard to articulate or think that it isn’t worth articulating.

Slide 18

Effective interviewers

Interviewers should be open-minded, willing to listen to stakeholders and should not have pre-conceived ideas about the requirements.

They should prompt the interviewee with a question or a proposal and should not simply expect them to respond to a question such as ‘what do you want’.

Slide 19

Use Cases - Background

Alistair Cockburn claims to have encountered over 18 different definitions of use case, given by different, each expert, teachers and consultants.

They differed along 4 dimensions: • Purpose• Contents• Plurality• Structure.

Slide 20

Use Cases - Purpose

Is the purpose of use cases to gather user stories, or build requirements?

Dimension Values: • Stories• Requirements

Slide 21

Use Cases - Contents

Are the contents of the use case required to be consistent, or can they be self-contradicting?

If consistent, are they in plain prose or are they in a formal notation?

Dimension Values:• Contradicting• Consistent prose• Formal content

Slide 22

Use Cases - Plurality

Is a use case really just another name for a scenario, or does a use case contain more than one scenario?

Dimension Values: • One • Multiple

Slide 23

Use Cases - Structure

Does a collection of use cases have a formal structure, an informal structure, or do they form an unstructured collection?

Dimension Values: • Unstructured• Semi-formal• Formal structure

Slide 24

Cockburn in Use Case Space

Purpose = requirementsContents = consistent prosePlurality = multiple scenarios per use caseStructure = semi-formal

Slide 25

Actors

External Actors• A person, a group of people or a system of any kind.

Internal Actors• May be the system in design, a subsystem or an object. • The system in design consists of subsystems, which

consist of objects. Actors have behavior(s).

• The top-level behavior is a responsibility. A responsibility contains goals, which contain

actions. • An action triggers an interaction. • The interaction is one actor’s goal calling upon another

actors (or its own) responsibility.

Slide 26

Scenario

A sequence of interactions happening under certain conditions, to achieve the initiating actor’s goal, and having a particular result with respect to that goal.

The interactions start from the triggering action and continue until the goal is delivered or abandoned, and the system completes whatever responsibilities it has with respect to the interaction.

AKA: Use Case Instance

Slide 27

Use Case

A collection of possible scenarios between the system under discussion (SuD) and initiating actor.

Characterized by the goal the initiating actor has toward the SuD’s declared responsibilities.

Shows how the initiating actor’s goal might be delivered or might fail.

Slide 28

Scenario/Use Case Bounds

All the interactions relate to the same goal. Interactions start at the triggering event and

end when the goal is delivered or abandoned, and the SuD completes its responsibilities with respect to the interaction.

Slide 29

Use Case

A set of use-case instances, where each instance is a sequence of actions a system performs that yields an observable result of value to a particular actor

A key attitude in use case work is to focus on the question • “How can using the system provide observable value to

the user, or fulfill their goals?”• As opposed to thinking of system requirements in terms

of a “laundry list” of features or functions.

Slide 30

LIBSYS use cases

Article printing

Article search

User administration

Supplier Catalogue services

LibraryUser

LibraryStaff

Slide 31

LIBSYS Use Case (1)

Initial assumption: The user has logged on to the LIBSYS system and has located the journal containingthe copy of the article.

Normal: The user selects the article to be copied. He or she is then prompted by the system to ei therprovide subscriber information for the journal or to indicate how they will pay for the article. Alternativepayment methods are by credit card or by quoting an organisational account number.

The user is then asked to fill in a copyright form that maintains details of the transaction and they thensubmit this to the LIBSYS system.

The copyright form is c hecked and, if OK, the PDF version of the article is downloaded to the LIBSYSworking area on the userÕs computer and the user is informed that it is available. The user is asked to selecta printer and a copy of the article is printed. If the article has been flagged as Ōprint-onlyÕ it is deleted fromthe userÕs system once the user has confirmed that printing is complete.

Slide 32

LIBSYS Use Case (2)

What can go wrong: The user may fail to fill in the copyright form correctly. In this case, the form shouldbe re-presented to the user for correction. If the resubmitted form is s till incorrect then the userÕs requestfor the article is rejected.

The payment may be rejected by the system. The userÕs request for the article is rejected.

The article download may fail. Retry until successful or the user terminates the session.

It may not be possible to print the article. If the article is not flagged as Ōprint-onlyÕ then it is held in theLIBSYS workspace. Otherwise, the article is deleted and the userÕs account credited with the cost of thearticle.

Other activities: Simultaneous downloads of other articles.

System state on completion: User is logged on. The downloaded article has been deleted from LIBSYSworkspace if it has been flagged as print-only.

Slide 33

Requirements validation

Concerned with demonstrating that the requirements define the system that the customer really wants.

Requirements error costs are high so validation is very important• Fixing a requirements error after delivery may

cost up to 100 times the cost of fixing an implementation error.

Slide 34

Requirements checking

Validity. Does the system provide the functions which best support the customer’s needs?

Consistency. Are there any requirements conflicts? Completeness. Are all functions required by the

customer included? Realism. Can the requirements be implemented

given available budget and technology Verifiability. Can the requirements be checked?

Slide 35

Requirements validation techniques

Requirements reviews• Systematic manual analysis of the

requirements. Prototyping

• Using an executable model of the system to check requirements.

Test-case generation• Developing tests for requirements to check

testability.

Slide 36

Requirements reviews

Regular reviews should be held while the requirements definition is being formulated.

Both client and contractor staff should be involved in reviews.

Reviews may be formal (with completed documents) or informal. Good communications between developers, customers and users can resolve problems at an early stage.

Slide 37

Review checks

Verifiability. Is the requirement realistically testable?

Comprehensibility. Is the requirement properly understood?

Traceability. Is the origin of the requirement clearly stated?

Adaptability. Can the requirement be changed without a large impact on other requirements?

Slide 38

Requirements management

Requirements management is the process of managing changing requirements during the requirements engineering process and system development.

Requirements are inevitably incomplete and inconsistent• New requirements emerge during the process as

business needs change and a better understanding of the system is developed;

• Different viewpoints have different requirements and these are often contradictory.

Slide 39

Requirements change

The priority of requirements from different viewpoints changes during the development process.

System customers may specify requirements from a business perspective that conflict with end-user requirements.

The business and technical environment of the system changes during its development.

Slide 40

Enduring and volatile requirements

Enduring requirements. Stable requirements derived from the core activity of the customer organisation. E.g. a hospital will always have doctors, nurses, etc. May be derived from domain models

Volatile requirements. Requirements which change during development or when the system is in use. In a hospital, requirements derived from health-care policy

Slide 41

Requirements classification

RequirementType

Description

Mutablerequirements

Requirements that change because of changes to the environment in which theorganisation is operating. For example, in hospital systems, the funding of patientcare may change and thus require different treatment information to be collected.

Emergentrequirements

Requirements that emerge as the customer's understanding of the system developsduring the system development. The design process may reveal new emergentrequirements.

Consequentialrequirements

Requirements that result from the introduction of the computer system. Introducingthe computer system may change the organisations processes and open up new waysof working which generate new system requirements

Compatibilityrequirements

Requirements that depend on the particular systems or business processes within anorganisation. As these change, the compatibility requirements on the commissionedor delivered system may also have to evolve.

Slide 42

Requirements management planning

During the requirements engineering process, you have to plan:• Requirements identification

• How requirements are individually identified;

• A change management process• The process followed when analysing a requirements

change;

• Traceability policies• The amount of information about requirements relationships

that is maintained;

• CASE tool support• The tool support required to help manage requirements

change;

Slide 43

Traceability

Traceability is concerned with the relationships between requirements, their sources and the system design

Source traceability• Links from requirements to stakeholders who proposed

these requirements; Requirements traceability

• Links between dependent requirements; Design traceability

• Links from the requirements to the design;

Slide 44

CASE tool support

Requirements storage• Requirements should be managed in a secure, managed

data store. Change management

• The process of change management is a workflow process whose stages can be defined and information flow between these stages partially automated.

Traceability management• Automated retrieval of the links between requirements.

Slide 45

Requirements change management

Should apply to all proposed changes to the requirements.

Principal stages• Problem analysis. Discuss requirements

problem and propose change;• Change analysis and costing. Assess effects of

change on other requirements;• Change implementation. Modify requirements

document and other documents to reflect change.

Slide 46

Key points

The requirements engineering process includes a feasibility study, requirements elicitation and analysis, requirements specification and requirements management.

Requirements elicitation and analysis is iterative involving domain understanding, requirements collection, classification, structuring, prioritisation and validation.

Systems have multiple stakeholders with different requirements.

Slide 47

Key points

Requirements validation is concerned with checks for validity, consistency, completeness, realism and verifiability.

Business changes inevitably lead to changing requirements.

Requirements management includes planning and change management.

Slide 48

Use Cases – the Big Picture

Many high-level use cases start with simple situations and straightforward, natural-language questions. • This is Jill. • This is her phone.• What does Jill want to do with her phone? • What steps must she take to achieve this goal? • How will her pathway toward this goal follow the

business logic fundamental to our project's success?

Slide 49


Use cases tend to account for various kinds of failure modes and defaults in user flow.

But the very context in which these failure modes occur tends to be rather cooked and artificial.

Many start with a neatly conventional circumstance • "Jill wants to buy a new ringtone"

They end in a similarly pat fulfillment • "Jill successfully downloads and installs the ringtone"

Slide 50


What about use cases that start out like: "Greta wants to sneak out and meet her lover

Patrick, without making her husband Bertrand suspicious."

"Kenji wants his private contact information to be more available to his close friends than the random boys he picks up clubbing."

"Claudia wants to play games on her computer at work, while making it seem as if she's busy getting things done."

Slide 51


Experience tells us that these are the kinds of things people actually do with technology.

Human beings are endlessly creative, contrary, even perverse.

Our motives are not always noble. We figure out ways to use whatever technology

happens to be at hand to further our goals• whether or not those goals bear any resemblance to what

we're "supposed to be" doing.

Slide 52


Consider the uses foreseen by designers, manufacturers and retailers for a new technology• Inevitably featured in the advertising and

marketing campaigns They often turn out to be much less

interesting than what people actually do with them.

Slide 53


Fault lines are all the gaps between the assumptions and the reality

Fault lines are places where emergent patterns of use expose • incorrect assumptions on the part of the designers• imperfect models of the target audience on the part of

marketers• social realities that might otherwise have remained latent

Fault lines also crop up where tech-savvy developers forget to take off their expert hat.• They consequently fail to understand the mental models

users carry around with them regarding how technology works.

Slide 54


There is good business sense in attending carefully to these fault lines.

That is where the truly useful products and services wait to be born.

Slide 55

Example

Cingular Wireless, US. Offers a service called "Escape-a-Date.” Provides its subscribers an emergency exit from bad

dates and similarly awkward social circumstances. The subscriber schedules a "rescue" phone call for a

pre-set time.• When their phone rings they are guided through a script

that gives them a convenient excuse to get up and leave. A social discomfort is circumvented, Everybody gets to save face.

Slide 56

Example

We laugh, but this is a real circumstance, something we can all recognize.

Someone, somewhere, has identified a genuine social need and devised response to it.

There is the “side effect” of shifting some packets and producing some revenue for the service provider!

A definite improvement on use cases which imagine or fabricate "needs" nobody actually ever had, which produce "features" and "conveniences" nobody ever uses.

Slide 57

Case in Point

Camera phones. At some point in the last five years, bundling a camera and a

mobile phone became technically feasible. Soon thereafter, it became a potential source of profit

• thus the current proliferation of models. But there never was a realistic scenario in which these

cameras become part of the everyday pattern of use for the majority of users.

That's why we see the use profile we almost invariably do.• interest in the phone's camera spikes immediately after

purchase, as customers explore the novelty and seek to justify the extra expenditure

• then tapers off asymptotically to zero.

Slide 58

A Basic Problem with Use Cases

They generally fail to anticipate the larger social context inside which all technology exists.

Another example: We have any number of good models for why and

how a user would go about sending an email, or using a mobile phone.

But no such model could have predicted the insidious way in which always-on availability that arrives alongside them affects even non-users.

Slide 59


What scenario would have predicted the emerging etiquette of "reachability“ that says serious adults must both own a mobile phone and carry it at all times?

What use case would have accounted for the resentment towards those who either refuse or simply forget to do so?

Slide 60


What designer would have captured and accurately modeled the annoyance your correspondents experience when you don't answer their messages in something closely approximating real time?

Remember, one of the original selling points of email was precisely that it was asynchronous. • One didn't have to be sitting in front of one's computer to

benefit from it. How things have changed!

Slide 61

The Moral of the Story

... is not to abandon use cases!! They'll remain vital tools for anyone seeking to

understand the delicate interactions between human beings and the things we use.

They will probably assume even greater importance over time, as our artifacts become ever more complicated.

But it would be both unexpected and fun if some of the features and functionality we are sure to be offered were based on a fuller, more robust appreciation of everyday life.

Documents

Slide 1 Requirements Engineering Processes. Slide 2 Something to Think About … The indispensable first step to getting the things you want out of life: