Coming up: What is a requirement? 1

Software Engineering: A Practitioner’s Software Engineering: A Practitioner’s Approach, 7/eApproach, 7/e

Chapter 5Chapter 5Requirements EngineeringRequirements Engineering

Modified to include Modified to include some Agile Conceptssome Agile Concepts

copyright © 1996, 2001, 2005R.S. Pressman & Associates, Inc.

NOTE: Some slides referenced from: Ian Sommerville Slides for Software Engineering.

Last weekLast week Software process modelsSoftware process models UMLUML

Class diagramsClass diagrams

AAA 2

This weekThis week RequirementsRequirements UMLUML

Use casesUse cases

Guest speaker!Guest speaker!

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What is the most difficult part What is the most difficult part of developing software?of developing software?

AAA 4

Coming up: Requirements come in many forms 5

What is a requirement?What is a requirement? Requirements are used to Requirements are used to describe all describe all

aspects of a systemaspects of a system They may range from a high-level abstract They may range from a high-level abstract

statement of a service or of a system statement of a service or of a system constraint to a detailed mathematical functional constraint to a detailed mathematical functional specificationspecification

They serve many rolesThey serve many roles May be the basis for a bid for a contract - therefore must be open to May be the basis for a bid for a contract - therefore must be open to

interpretationinterpretation May be the basis for the contract itself - therefore must be defined in May be the basis for the contract itself - therefore must be defined in

detaildetail Are always used to communicate what you intend to buildAre always used to communicate what you intend to build

Requirements come in many Requirements come in many formsforms

Requirements Statements Requirements Statements ex: “The system shall ….”ex: “The system shall ….”

UML Use-case diagramsUML Use-case diagrams eXtreme Programming “User Stories”eXtreme Programming “User Stories”

Any other documents that communicate what you Any other documents that communicate what you intend to buildintend to build Prototypes can be used as requirementsPrototypes can be used as requirements Existing systems can serve as requirements “Build this Existing systems can serve as requirements “Build this

system, but use Java instead of Fortran”system, but use Java instead of Fortran” UML Sequence diagrams, State charts, activity diagrams…UML Sequence diagrams, State charts, activity diagrams…

6Coming up: All Requirements

Coming up: Typical Requirements Statements 7

All RequirementsAll Requirements Should specify Should specify external behavior external behavior of the of the

systemsystem what the system does, not how what the system does, not how

Includes functional and non-functional requirementsIncludes functional and non-functional requirements FunctionalFunctional requirements are statements of the requirements are statements of the

services that the system must provideservices that the system must provide What must the system do? (Start all with the phrase What must the system do? (Start all with the phrase

“The system shall…”)“The system shall…”) Non-functionalNon-functional requirements are constraints on requirements are constraints on

the services and functions offered by the systemthe services and functions offered by the system How must it do it? or a constraint on the systemHow must it do it? or a constraint on the system

Coming up: Why do we care? 8

Typical Requirements Typical Requirements StatementsStatements

FunctionalFunctional: The system shall display the heart : The system shall display the heart rate, blood pressure and temperature of a rate, blood pressure and temperature of a patient connected to the patient monitor.patient connected to the patient monitor.

Non-Functional:Non-Functional: "Display of the patient's vital "Display of the patient's vital signs must respond to a change in the signs must respond to a change in the patient's status within 2 seconds.”patient's status within 2 seconds.” ‘‘ilities’ - ilities’ - Performance, Scalability, Capacity, Performance, Scalability, Capacity,

Availability Reliability, Recoverability, Availability Reliability, Recoverability, Maintainability, Serviceability, Security,Regulatory, Maintainability, Serviceability, Security,Regulatory, ManageabilityManageability

What are some functional requirements on an iPod? Non-functional?

Coming up: Prescriptive versus Agile approach 9

Why do we care?Why do we care? Most large software systems address wicked Most large software systems address wicked

problemsproblems Problems which are so complex that they Problems which are so complex that they

can never be fully understood and where can never be fully understood and where understanding develops during the system understanding develops during the system developmentdevelopment

Therefore, requirements are normally both Therefore, requirements are normally both incomplete and inconsistentincomplete and inconsistent

Requirements help by giving you the best Requirements help by giving you the best understanding you can have at the beginningunderstanding you can have at the beginning

Change in requirementsChange in requirements Recall the process models we discussed last Recall the process models we discussed last

weekweek Are they good at handling changing requirements?Are they good at handling changing requirements? Do you think these prescriptive models would work Do you think these prescriptive models would work

when trying to reverse engineer a system?when trying to reverse engineer a system? i.e., “build this system but in Java”i.e., “build this system but in Java”

AAA 10

Prescriptive versus Agile Prescriptive versus Agile approachapproach

Prescriptive – approach is to Prescriptive – approach is to minimize/prevent change minimize/prevent change by understanding system thoroughly at the beginningby understanding system thoroughly at the beginning Typically heard: “A change during implementation costs 10 Typically heard: “A change during implementation costs 10

times more than a change during requirements phase”times more than a change during requirements phase”

Agile – approach is to Agile – approach is to manage changemanage change by being flexible (i.e. Agile)by being flexible (i.e. Agile) Typically heard: Requirements planned for 6 months from Typically heard: Requirements planned for 6 months from

now are most likely completely inaccurate. Don’t waste now are most likely completely inaccurate. Don’t waste resources planning far ahead. Plan short iterations and adjust resources planning far ahead. Plan short iterations and adjust the plan as you go.the plan as you go.

11Coming up: Typical PrescriptiveRequirements Engineering Process

Coming up: Requirements Engineering-II 12

Typical PrescriptiveTypical PrescriptiveRequirements Engineering Requirements Engineering

ProcessProcess InceptionInception—ask a set of questions that establish …—ask a set of questions that establish … basic understanding of the problembasic understanding of the problem the people who want a solutionthe people who want a solution the nature of the solution that is desired, and the nature of the solution that is desired, and the effectiveness of preliminary communication the effectiveness of preliminary communication

and collaboration between the customer and and collaboration between the customer and the developerthe developer

ElicitationElicitation—elicit requirements from all stakeholders—elicit requirements from all stakeholders to identify the problemto identify the problem propose elements of the solutionpropose elements of the solution negotiate different approaches, andnegotiate different approaches, and specify a preliminary set of solution requirementsspecify a preliminary set of solution requirements

ElaborationElaboration—create an analysis model that identifies data, functional —create an analysis model that identifies data, functional and behavioral requirementsand behavioral requirements

NegotiationNegotiation—agree on a set of requirements among all stakeholders —agree on a set of requirements among all stakeholders (realistic, non-conflicting, inline with budget)(realistic, non-conflicting, inline with budget)

Coming up: Typical Prescriptive System Requirements Specification (SRS) Document Structure 13

Requirements Engineering-IIRequirements Engineering-II SpecificationSpecification—can be any one (or more) of the following:—can be any one (or more) of the following:

A written documentA written document A set of modelsA set of models A formal mathematical proofA formal mathematical proof A collection of user scenarios (use-cases)A collection of user scenarios (use-cases) A prototypeA prototype

ValidationValidation—a review mechanism that looks for—a review mechanism that looks for errors in content or interpretationerrors in content or interpretation areas where clarification may be requiredareas where clarification may be required missing informationmissing information inconsistencies (a major problem when large products or systems inconsistencies (a major problem when large products or systems

are engineered)are engineered) conflicting or unrealistic (unachievable) requirements. conflicting or unrealistic (unachievable) requirements.

Requirements managementRequirements management Similar to source code managementSimilar to source code management

Coming up: Analysis Model 14

Typical Prescriptive System Typical Prescriptive System Requirements Specification (SRS) Requirements Specification (SRS)

Document StructureDocument Structure PurposePurpose Overall DescriptionOverall Description System Features (Functional Requirements/Use System Features (Functional Requirements/Use

Cases)Cases) External Interface Requirements External Interface Requirements

User interface requirements or standardsUser interface requirements or standards Hardware interfaces to other systemsHardware interfaces to other systems Software interfaces to other systemsSoftware interfaces to other systems Communication InterfacesCommunication Interfaces

Non-functional RequirementsNon-functional Requirements Appendices - analysis model diagramsAppendices - analysis model diagrams See SRS Template on CS421 See SRS Template on CS421 ProjectProject Page Page

(provided by (provided by http://www.processimpact.com/ … but essentially from IEEE). … but essentially from IEEE).

Coming up: Use-Cases 15

Analysis ModelAnalysis Model Included to provide more clarification Included to provide more clarification

about textual requirements (where about textual requirements (where needed)needed)

Elements of the analysis modelElements of the analysis model Scenario-based elementsScenario-based elements

Functional—processing narratives for software functionsFunctional—processing narratives for software functions Use-case—descriptions of the interaction between an Use-case—descriptions of the interaction between an

“actor” and the system“actor” and the system Class-based elements – Class-based elements – e.g. class diagrame.g. class diagram Behavioral elements – Behavioral elements – e.g. se.g. state diagram, sequence tate diagram, sequence

diagram, activity diagram, etc..diagram, activity diagram, etc.. Flow-oriented elementsFlow-oriented elements – e.g. data flow diagram – e.g. data flow diagram

Coming up: Use-Case Diagram 16

Use-CasesUse-Cases A collection of usage scenarios that describe the thread of usage of a systemA collection of usage scenarios that describe the thread of usage of a system Each scenario is described from the point-of-view of an “actor”—a person or Each scenario is described from the point-of-view of an “actor”—a person or

device that interacts with the software in some waydevice that interacts with the software in some way Each scenario answers the following questions:Each scenario answers the following questions:

Who is the primary actor, the secondary actor (s)?Who is the primary actor, the secondary actor (s)? What are the actor’s goals?What are the actor’s goals? What preconditions should exist before the story begins?What preconditions should exist before the story begins? What main tasks or functions are performed by the actor?What main tasks or functions are performed by the actor? What extensions might be considered as the story is What extensions might be considered as the story is

described?described? What variations in the actor’s interaction are possible?What variations in the actor’s interaction are possible? What system information will the actor acquire, produce, or change?What system information will the actor acquire, produce, or change? Will the actor have to inform the system about changes in the external Will the actor have to inform the system about changes in the external

environment?environment? What information does the actor desire from the system?What information does the actor desire from the system? Does the actor wish to be informed about unexpected changes?Does the actor wish to be informed about unexpected changes?

Coming up: Use Case Description 17

Use-Case DiagramUse-Case Diagram

homeowner

Arms/ disarms system

Accesses system via Internet

Reconfigures sensors and related

system features

Responds toalarm event

Encounters anerror condition

system administrator

sensors

Each oval is a separate use case that has a description

Each stick figure is an actor in your system

The block is an external system that interacts with your system. Any system you aren’t developing is external

Use Case DescriptionUse Case Description ID - ID - A unique to reference this use case U01, U02, etc… ObjectiveObjective - What is the ultimate objective of the use-case. What is it - What is the ultimate objective of the use-case. What is it

trying to achieve? trying to achieve? PriorityPriority – The overall priority of this use-case (Low, Medium, High)– The overall priority of this use-case (Low, Medium, High) SourceSource – Who is the main source of this use case. Who cares most – Who is the main source of this use case. Who cares most

about this functionality? This should be the one person you would about this functionality? This should be the one person you would ask if there is a question about this use-case. (Make up a name and ask if there is a question about this use-case. (Make up a name and cite their: John Smith (End-user) here.)cite their: John Smith (End-user) here.)

ActorsActors – Which actors/stakeholders are involved in the use-case?– Which actors/stakeholders are involved in the use-case? Flow of Events Flow of Events

Basic FlowBasic Flow - flow of events normally executed in the use-case - flow of events normally executed in the use-case Alternative Flow(s)Alternative Flow(s) - a secondary flow of events due to infrequent - a secondary flow of events due to infrequent

conditionsconditions Exception Flow(s)Exception Flow(s) - Exceptions that may happen during the execution of the - Exceptions that may happen during the execution of the

use case use case IncludesIncludes - other use case IDs that are referenced in steps in the - other use case IDs that are referenced in steps in the

flow of events.flow of events. PreconditionsPreconditions - Any condition that must be satisfied before the use - Any condition that must be satisfied before the use

case begins. If the condition is “User is logged in”, then the first step case begins. If the condition is “User is logged in”, then the first step of the use case is NOT “User logs in”. They are already logged in if of the use case is NOT “User logs in”. They are already logged in if that is a pre-condition!that is a pre-condition!

Post conditionsPost conditions - The conditions that will be satisfied after the use - The conditions that will be satisfied after the use case successfully completes (typically same as objective)case successfully completes (typically same as objective)

Notes/IssuesNotes/Issues - Any relevant notes or issues that need to be resolved- Any relevant notes or issues that need to be resolved 18Coming up: Alternate and Exception Flows

Alternate and Exception FlowsAlternate and Exception Flows1.1. Basic FlowBasic Flow

1.1. User enters user nameUser enters user name2.2. User enters password User enters password 3.3. User submits the formUser submits the form4.4. Password is validated as correctPassword is validated as correct5.5. Main menu is displayedMain menu is displayed

2.2. Alternate Flow 1: No password is present at step Alternate Flow 1: No password is present at step 1.41.41.1. System displays error message.System displays error message.2.2. System continues at step 1.2System continues at step 1.2

3.3. Alternate Flow 2: Password is incorrect as step 1.4Alternate Flow 2: Password is incorrect as step 1.41.1. ……

4.4. Exception Flow 1: Database is unreachableException Flow 1: Database is unreachable1.1. System displays an unrecoverable error and exits.System displays an unrecoverable error and exits.

Coming up: Includes versus Preconditions 19

Show when in the basic flow this happens and where you end up after the alt flow

You may not know when this happens. That’s okay

Includes versus PreconditionsIncludes versus Preconditions

Basic Flow User selects option

4 from main menu screen

… Preconditions:

User is logged in Includes:

None

Coming up: eXtreme Programming (XP): User Stories 20

Basic Flow User executes U2:

Login User selects option 4

from main menu screen

… Preconditions:

None Includes:

U2: LoginDon’t forget to show this on the use case diagram as “includes”

Includes are steps in the use-casePre-conditions happen before the use caseItems are one or the other, not both!

eXtreme Programming (XP): eXtreme Programming (XP): User StoriesUser Stories

Serve as requirements within the XPServe as requirements within the XP processprocess

Written by Written by customerscustomers Time Estimated by Time Estimated by developersdevelopers Replaces large requirements documentsReplaces large requirements documents Represents anything that is “progress” to the Represents anything that is “progress” to the

customercustomer Examples: Examples:

Students can purchase monthly parking passes online.Students can purchase monthly parking passes online. Parking passes can be paid via credit cards.Parking passes can be paid via credit cards. Parking passes can be paid via PayPalParking passes can be paid via PayPal Professors can input student marks.Professors can input student marks. Students can obtain their current seminar schedule.Students can obtain their current seminar schedule. Students can order official transcripts.Students can order official transcripts.

21Coming up: eXtreme Programming (XP): User Stories

eXtreme Programming (XP): eXtreme Programming (XP): User StoriesUser Stories

Short – 1 or 2 sentences. Usually Short – 1 or 2 sentences. Usually supposed to fit on a 3x5 notecardsupposed to fit on a 3x5 notecard

Easy to estimate (project velocity)Easy to estimate (project velocity) Allows requirements to change frequently Allows requirements to change frequently

with less impactwith less impact Without accompanying validation tests may Without accompanying validation tests may

lead to misinterpretationlead to misinterpretation Difficult to scale to very large projectsDifficult to scale to very large projects Requires close customer contact to ensure Requires close customer contact to ensure

correct implementationcorrect implementation22

Coming up: Format for User Stories (CS421 only… not standard!)

Format for User Stories Format for User Stories (CS421 only… not standard!)(CS421 only… not standard!)

Unique IdentifierUnique Identifier Source Source – who should developer contact with questions – who should developer contact with questions

about this?about this? Story Story – short (1-3 sentence) high-level description of – short (1-3 sentence) high-level description of

story. When the developer plans to implement they story. When the developer plans to implement they should discuss with the customer the details. should discuss with the customer the details. As a [user role], I want to [goal], so I can [reason].As a [user role], I want to [goal], so I can [reason].

Time estimate Time estimate – how long in “ideal development time” – – how long in “ideal development time” – time without meetings or any interruptions time without meetings or any interruptions

Client’s Priority Client’s Priority – how important is the story to the – how important is the story to the client? (Low, Medium, High) client? (Low, Medium, High)

Coming up: The web has MANY references about User Stories and Use Cases. 23

The web has MANY references The web has MANY references about User Stories and Use about User Stories and Use

Cases. Cases. User Stories: User Stories: http://www.agile-software-http://www.agile-software-

development.com/search/label/user%20storiesdevelopment.com/search/label/user%20stories

Use Cases: Use Cases: http://alistair.cockburn.us/Use+case+fundamentalshttp://alistair.cockburn.us/Use+case+fundamentals

Which is better? Many arguments – here is one: Which is better? Many arguments – here is one: http://alistair.cockburn.us/Why+I+still+use+use+cashttp://alistair.cockburn.us/Why+I+still+use+use+caseses

Coming up: Characteristics of requirements 24

Characteristics of Characteristics of requirementsrequirements

Coming up: Negotiating Requirements 25

Coming up: Requirements Rationale 26

Negotiating RequirementsNegotiating Requirements Identify the key stakeholdersIdentify the key stakeholders

These are the people who will be involved in the negotiationThese are the people who will be involved in the negotiation Determine each of the stakeholders’ “win Determine each of the stakeholders’ “win

conditions”conditions” Win conditions are not always obviousWin conditions are not always obvious

NegotiateNegotiate Work toward a set of requirements that lead to Work toward a set of requirements that lead to

““win-win”win-win” Different stakeholders have different ideas of Different stakeholders have different ideas of

what they wantwhat they want

Coming up: Non-Functional Requirement Types 27

Requirements RationaleRequirements Rationale It is important to provide rationale with It is important to provide rationale with

requirements requirements This helps the developer understand the This helps the developer understand the

application domain and why the requirement is application domain and why the requirement is stated in its current formstated in its current form

Particularly important when requirements have to be Particularly important when requirements have to be changed. The availability of rationale reduces the chances changed. The availability of rationale reduces the chances that change will have unexpected effectsthat change will have unexpected effects

In this class we’ll provide the requirement’s source and In this class we’ll provide the requirement’s source and assume they can contact the source to get a rationale if assume they can contact the source to get a rationale if needed instead of an explicit “rationale”. This is more “agile”needed instead of an explicit “rationale”. This is more “agile”

Coming up: Non-Functional Requirement Examples 28

Non-Functional Non-Functional Requirement TypesRequirement Types

Product requirementsProduct requirements Requirements which specify that the delivered product Requirements which specify that the delivered product

must behave in a particular way e.g. execution speed, must behave in a particular way e.g. execution speed, reliability, etc.reliability, etc.

Organizational requirementsOrganizational requirements Requirements which are a consequence of Requirements which are a consequence of

organizational policies and procedures e.g. organizational policies and procedures e.g. process standards used, implementation process standards used, implementation requirements, etc.requirements, etc.

External requirementsExternal requirements Requirements which arise from factors which are Requirements which arise from factors which are

external to the system and its development process e.g. external to the system and its development process e.g. interoperability requirements, legislative requirements, interoperability requirements, legislative requirements, etc.etc.

Remember: Non Functional = Constraints on the system

Coming up: Requirements must be testable 29

Non-Functional Non-Functional Requirement ExamplesRequirement Examples

Product requirementProduct requirement 4.C.8 It shall be possible for all necessary communication 4.C.8 It shall be possible for all necessary communication

between the APSE and the user to be expressed in the standard between the APSE and the user to be expressed in the standard Ada character set.Ada character set.

Organizational requirementOrganizational requirement 9.3.2 The system development process and deliverable 9.3.2 The system development process and deliverable

documents shall conform to the process and deliverables defined documents shall conform to the process and deliverables defined in XYZCo-SP-STAN-95.in XYZCo-SP-STAN-95.

External requirementExternal requirement 7.6.5 The system shall provide facilities that allow any user to 7.6.5 The system shall provide facilities that allow any user to

check if personal data is maintained on the system. A procedure check if personal data is maintained on the system. A procedure must be defined and supported in the software that will allow must be defined and supported in the software that will allow users to inspect personal data and to correct any errors in that users to inspect personal data and to correct any errors in that data.data. security, maintainability

constraint: quality

constraint: interoperability

Agile stories? How?

Coming up: Requirements: testable metrics 30

Requirements must be Requirements must be testabletestable Traditional requirements must be written so that they can Traditional requirements must be written so that they can

be objectively verified. be objectively verified.

XP requirements have explicit acceptance test XP requirements have explicit acceptance test cases written by the customers to solve this cases written by the customers to solve this problem.problem.

The problem with this requirement is its use of vague The problem with this requirement is its use of vague terms such as ‘errors shall be minimized”terms such as ‘errors shall be minimized” The system should be easy to use by experienced The system should be easy to use by experienced

controllers and should be organized in such a way that user controllers and should be organized in such a way that user errors are minimized.errors are minimized.

The error rate should be been quantifiedThe error rate should be been quantified Experienced controllers should be able to use all the system Experienced controllers should be able to use all the system

functions after a total of two hours training. After this functions after a total of two hours training. After this training, the average number of errors made by training, the average number of errors made by experienced users should not exceed two per day.experienced users should not exceed two per day.

Coming up: Requirements Validation 31

Requirements: testable Requirements: testable metricsmetrics

Property MeasureSpeed Processed transactions/second

User/Event response timeScreen refresh time

Size K BytesNumber of RAM chips

Ease of use Training timeNumber of help frames

Reliability Mean time to failureProbability of unavailabilityRate of failure occurrenceAvailability

Robustness Time to restart after failurePercentage of events causing failureProbability of data corruption on failure

Portability Percentage of target dependent statementsNumber of target systems

Coming up: Validating Requirements-I 32

Requirements ValidationRequirements Validation Ensure the requirements define the Ensure the requirements define the

system that the customer really wantssystem that the customer really wants

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

delivery may cost up to 100 times the cost delivery may cost up to 100 times the cost of fixing an implementation errorof fixing an implementation error

Coming up: Requirements final thoughts… 33

Validating Requirements-IValidating Requirements-I Is each requirement consistent with the overall objective for Is each requirement consistent with the overall objective for

the system/product? Work with all parties on this question!the system/product? Work with all parties on this question!

Is each requirement bounded and unambiguous? (e.g. Is each requirement bounded and unambiguous? (e.g. testable)testable)

Does each requirement have attribution? That is, is a source Does each requirement have attribution? That is, is a source (generally, a specific individual) noted for each requirement? (generally, a specific individual) noted for each requirement?

Do any requirements conflict with other requirements?Do any requirements conflict with other requirements?

Is each requirement testable, once implemented?Is each requirement testable, once implemented?

Does the requirements model cover the system to be Does the requirements model cover the system to be built (information, function and behavior).built (information, function and behavior).

Requirements errors are cheaper to fix before implementation and deployment

Coming up: Requirements final thoughts… 34

Requirements final thoughts…Requirements final thoughts… Requirements should specify one and only one thingRequirements should specify one and only one thing

Requirements and User Stories Requirements and User Stories can only pass or failcan only pass or fail, they , they can’t partially pass. If you want to partially pass a can’t partially pass. If you want to partially pass a requirement split into tworequirement split into two

Requirements must be Requirements must be testabletestable Requirements must specify what Requirements must specify what YOUR system YOUR system

must domust do, not what other (external) systems do, not what other (external) systems do To make this easier, in this class all functional To make this easier, in this class all functional

requirements must begin with requirements must begin with “The system shall…”“The system shall…” Must have a Must have a sourcesource (make it up for CS421) (make it up for CS421)

Coming up: Requirements must have a unique ID 35

Requirements final thoughts… Requirements final thoughts… Should not be a design choice (this is hard to get right). Should not be a design choice (this is hard to get right).

The system shall store user information including name, DOB, The system shall store user information including name, DOB, address and SSN. <-- Good!address and SSN. <-- Good!

The system shall store user information in an Oracle database The system shall store user information in an Oracle database including name, DOB, address, SSN. <-- including name, DOB, address, SSN. <-- badbad

Is Oracle really REQUIRED? Hard to say… maybe, but probably not. Is Oracle really REQUIRED? Hard to say… maybe, but probably not. This is a decision you would make at implementation design time. This is a decision you would make at implementation design time.

Question: Does the customer care that you use Oracle? MySQL? Etc.. Question: Does the customer care that you use Oracle? MySQL? Etc.. Maybe someone found some other MUCH BETTER approach storing Maybe someone found some other MUCH BETTER approach storing the data on moon rocks.the data on moon rocks.

Again: This is hard to avoid… and I’m not to concerned with it on the Again: This is hard to avoid… and I’m not to concerned with it on the SRS, but I want you to be very aware of when you are making design SRS, but I want you to be very aware of when you are making design choices instead of required features.choices instead of required features.

Coming up: Bad Example Requirements Statements 36

Requirements must have a Requirements must have a unique IDunique ID

Must have a unique ID. Must have a unique ID.

When testing you need to reference REQ-1 or REQ-287. When testing you need to reference REQ-1 or REQ-287. Multiple things cannot be labeled REQ-1. Multiple things cannot be labeled REQ-1.

Later our test cases will say: This Later our test cases will say: This test case validates requirements test case validates requirements REQ-1, REQ-27, and REQ-56. REQ-1, REQ-27, and REQ-56.

Coming up: Bad Examples 37

Bad Example Requirements Bad Example Requirements StatementsStatements

Bad requirements examples:Bad requirements examples: The system shall validate and accept credit cards and The system shall validate and accept credit cards and

cashier’s checks. High priority.cashier’s checks. High priority.

The system shall process all mouse clicks very fast to The system shall process all mouse clicks very fast to ensure user’s do not have to wait.ensure user’s do not have to wait.

The user must have Adobe Acrobat installed.The user must have Adobe Acrobat installed.

These don’t have a source or unique ID, but what else is wrong?

Coming up: SRS Functional Requirements Checklist 38

Bad ExamplesBad Examples The system shall validate and accept credit cards and The system shall validate and accept credit cards and

cashier’s checks. High priority.cashier’s checks. High priority. Problem: two requirements instead of one. Problem: two requirements instead of one. If the credit card processing works, but the cashier’s check If the credit card processing works, but the cashier’s check

validation does not… is this requirement pass or fail? Has to be validation does not… is this requirement pass or fail? Has to be fail, but that is misleading. fail, but that is misleading.

Maybe only credit cards are high priority and cashier’s checks Maybe only credit cards are high priority and cashier’s checks are low priority.are low priority.

The system shall process all mouse clicks very fast to ensure The system shall process all mouse clicks very fast to ensure user’s do not have to wait.user’s do not have to wait.

Problem: This is not testable. Quantify how fast is acceptable?Problem: This is not testable. Quantify how fast is acceptable? The user must have Adobe Acrobat installed. The user must have Adobe Acrobat installed.

Problem: This is not something our system must do. It could be Problem: This is not something our system must do. It could be in the constraints/assumptions or maybe operating environment in the constraints/assumptions or maybe operating environment sections, but is not a functional requirement of our systemsections, but is not a functional requirement of our system

SRS Functional Requirements SRS Functional Requirements ChecklistChecklist

All start with “The system shall…”All start with “The system shall…” All have a unique identifier (R1, R2, R3, …)All have a unique identifier (R1, R2, R3, …) All do one and only one thingAll do one and only one thing All are testableAll are testable Have a source (who asked for it? make it up for Have a source (who asked for it? make it up for

the SRS – John Smith (Marketing), Nguyen Kim the SRS – John Smith (Marketing), Nguyen Kim (sys admin), etc…(sys admin), etc…

Says something YOUR software shall doSays something YOUR software shall do Are all labeld “F” in the chartAre all labeld “F” in the chart

Coming up: SRS Non-functional Requirements Checkist 39

Check this when writing

the SRS

SRS Non-functional Requirements SRS Non-functional Requirements CheckistCheckist

Section 5 just categorizes items in the table:Section 5 just categorizes items in the table:

5.1 Performance Requirements5.1 Performance Requirements See section 7 R11-R17, R29, R4See section 7 R11-R17, R29, R4

5.2 Safety Requirements5.2 Safety Requirements See section 7 R18See section 7 R18

All the ones listed in section 5 should be marked “NF” All the ones listed in section 5 should be marked “NF” in section 7’s table and be non-functional constraintsin section 7’s table and be non-functional constraints

Intuition: Is this something I can assign to one Intuition: Is this something I can assign to one developer and say “code this”… if so, it’s functional. (A developer and say “code this”… if so, it’s functional. (A constraint?)constraint?)

Coming up: The Result of Good Requirements 40

Check this when writing

the SRS

End of presentation 41

The Result of Good The Result of Good RequirementsRequirements

I’m melting!

Your wicked problems melt into small manageable problems ….