5. Design1 Agenda for design activity r1. Tracing requirements r2. Managing requirements r3....

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5. Design 1

Agenda for design activity

1. Tracing requirements2. Managing requirements3. Requirements management tools4. Homework

5. Design 2

1. Tracing requirements

Types of tracingComplexity of tracingReasons for tracingObservationsSuggestions

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Types of tracing (1 of 2)

Req Req Req

Req ReqReq

Straight through

Expansion Focus Creation End

DesignDesign Design Design Design

Five types of tracingFive types of tracing

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Types of tracing (2 of 2)

Weight

Weight A Weight B

Spreadsheet

Calculation GraphingNo hazardous material

Straight through

Expansion

Focus Creation

DesignDesign

Design Design

Bedroom on east side

Instrumentation

Design

No hazardous material

Building supplies

Missile

An example of each typeAn example of each type

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Complexity of tracing (1 of 2)

SpecSpec

Often used in tracing and tracing

Simple tracing flows from spec to spec and doesn’t include tracing to design.

It’s the more common practice

Simple tracing flows from spec to spec and doesn’t include tracing to design.

It’s the more common practice

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Complexity of tracing (2 of 2)

Spec contract

Stakeholders

Design

Spec contract

Stakeholders

Design

Speccontract

Stakeholders

Design

Flow through design is more complex and is a less common practice. However, it produces less problems

Design of the higher product

Note: Flow within a rectangle or ellipse not shown

More complex but provides truer tracing picture

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Reasons for tracing (1 of 5)

Reason 1: tracing -- Where did requirement get implemented?• Less precise linkage criteria than tracing

for verification/validation• Often done by doing tracing first

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Reason 2: tracing for verification/validation -- What lower requirements are used in verifying/validating higher requirements?• Simplest and most repeatable

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Reason 3: tracing for origin -- Where did each requirement come from; why does it exist?• more linkages to explain how design

creates requirements

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Reason 4: tracing for change impact -- If one requirement changes, what other requirements must change?• More linkages to reflect impacts of

requirements on each other

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The four different reasons for tracing can result in four different sets of linkages

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Observations (1 of 4)

Tracing is a best practice• Supports verification and validation• Makes sure requirements are implemented• Prevents unnecessary requirements• Shows how changing one requirement

changes others• Meets customer expectation

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Tracing is expensive• Tracing is complex and expensive;

$benefit/$cost > 1?• Many believe cost far out weighs the

benefit; takes time, diverts resources, degrades engineers, and drives tools

• Lack of training & rules make trace not repeatable or dependable

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The following rules-of-thumb can cause trouble• All requirements must come from somewhere• All requirements must go somewhere• All requirements shall trace in one direction• Tracing shall be from spec to spec and not

within a spec• Tracing shall not be from spec to design• There shall be one “shall” per requirement• All requirements shall be individually traced

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Design is an essential part of flowdown and trace

Design is difficult to capture in requirements management tools

Few people use trace to understand the effect of a requirement change on other requirements

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Suggestion (1 of 3)

Set customer expectationsNegotiate with customer to minimize effort

for design and verificationDocument agreements -- in the spec if

possible using clarifications, definitions, and examples

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Suggestion (2 of 3)

Choose a type of tracing such as tracing to confirm verification and validation

Provide rules and trainingProvide for independent confirmation of

tracing

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Suggestion (3 of 3)

Req Req Req

Req Req

ExpansionFocusDesign Design

Req Req Req

Req Req

Expansion Focus

Flow expansion and focus through design -- not directlyFlow expansion and focus through design -- not directly1. Tracing requirements

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2. Managing requirements

Requirements attributesData interface attributesPhysical interface attributesDocumenting requirementsManaging requirements change

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Requirements attributes (1 of 2)

Requirement -- textTitle -- short textNumerical identifier -- added by management

toolProduct unique identifier (PUI) -- added by

engineersVerification method -- how requirement

verified

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Requirements attributes (2 of 2)

Owner -- person responsible for successStakeholders -- people with an interestChange history -- change datesFlowdown/traces -- flowdown and trace

linksRationale -- why requirement is the way it is

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Data interface attributes

Data itemCriteriaTimingUnits and enumerationFormatRangesAccuracy

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Physical interface attributes (1 of 2)Electrical• Signals• Power• EMI/EMC• Grounding

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Physical interface attributes (2 of 2)

Mechanical • Dimensions• Mounting• Alignment• Weight• Heating• Cooling

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Documenting requirements

Media• Paper• Office computer tools• Data base

Format• Contractor chosen• Commercial standard• MIL-STD-490A• MIL-STD-490B

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Managing requirements change

Often handled through configuration management

Techniques• Data base• Change pages• Red-line changes

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3. Requirements management tools

INCOSE tools surveyINCOSE tool-selection criteriaTools surveyed by INCOSESelection considerations for ease of useSelection considerations for compatibilitySelection criteria for satisfaction

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INCOSE tools survey

Comparison made by National Council on Systems Engineering (INCOSE)

Internet address: http\\www.incose.org/workgrps/tools/req_surv.htm

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INCOSE tool-selection criteria (1 of 2)

1. Capturing requirements identification2. Capturing system element structure3. Requirements flowdown4. Traceability analysis5. Configuration management6. Documents and other output media

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INCOSE tool-selection criteria (2 of 2)

7. Groupware8. Interfaces to other tools9. System environment10. User interfaces11. Standards12. Support and maintenance13. Other features

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Tools surveyed by INCOSE (1 of 2)

Cadence -- BonesBoeing North American, Inc. --

CASETSVitech -- COREMesa Systems Guild -- Cradle/SEEZycad -- DOORSTeknowledge -- ProductTrackImage That -- ExtendAscent Logic -- RDD-100Integrated Chipware Inc. -- RTMTD Technologies -- SLATE

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Tools surveyed by INCOSE (2 of 2)

Cadence -- SPWCompliance Automation -- VITAL LINKTeledyne Brown Engineering -- XTie-RTNu Thena Systems -- ForesightMathWorks -- MATLAB, Simulink,

Stateflow, Real-Time WorkshopRational (Requisite) -- RequisitePro V2.0Statemate -- Magnum

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Considerations for ease of use

UsingLearningPutting information into the toolExtracting information from the toolKnowing what information is in the tool Navigating among informationGrouping information for comparison and

reportsAssuring quality such as spell checking

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Considerations for compatibility

Computer and operating system being used on the project

Way team members work

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Considerations for satisfaction

Gain understanding of the tool before committing to use tool

Avoid choices based on demo by sales person

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4. Homework

DiagramCustomer wantsTimepiece specTimepiece contractDesignClock specAC adapter specProblem

4. Homework

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Diagram

Customer wantsC1, C2, C3

Timepiece specS1

Timepiece contractX1

Timepiece designD1, D2, D3, D4, D5

Clock specT1

Adapter specU1, U2

4. Homework

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Customer wants

C1: I want a timepiece that I can look at and determine time accurate to one minute per day since the last setting

C2: Cost, size, weight, mechanism, style, power, and everything else are of no consequence

C3: I will give a flat $100 for the timepiece regardless of design

4. Homework

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Timepiece spec

S1: The timepiece shall display time accurate to one minute per day since the last setting

4. Homework

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Timepiece contract

X1: Customer will pay $100 for timepiece meeting timepiece spec

4. Homework

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Design (1 of 2)

D1: I’ll design the timepiece using existing components.

D2: I want to make a lot of profitD3: The Dilmore catalogue shows that its least

expensive clock is the model 100 for $4. It is resettable to correct the time, is accurate to one minute per day since the last setting, but requires an AC adapter

4. Homework

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Design (2 of 2)

D4: The Hazel catalog shows the model 200 as its least expensive AC adapter compatible with the Dilmore model 100 clock, and the adapter costs $1.

D5: The model 200 AC adapter comes in either black or beige at no extra cost. In my opinion, beige is more attractive in the customer’s environment

4. Homework

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Clock spec

T1: Clock shall be a Dilmore model 100 clock

4. Homework

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AC adapter spec

U1: AC adapter shall be a Hazel model 200 AC adapter

U2: AC adapter shall be beige

4. Homework

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Problem (1 of 4)

1. What items need to be successfully implemented to verify item D5? -- a. T1, U1, & U2; b. U1 & U2; c. U1; d. U2

2. For tracing purposes, what items implement item X1? -- a. D3; b. D4, c. D3 & D4; d. D3, D4, & D5

4. Homework

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Problem (2 of 4)

3. For tracing purposes, where did the requirements for item D4 come from? -- a. D3; b. D1, D2, & D3; c. D1, D2, D3, & X1; d. S1, D1, D2, & D3

4. For tracing purposes, what items implement item C2? -- a. none of the listed items, b. S1 & X1, c. D1, D2, & D3; d. T1, U1, & U2

4. Homework

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Problem (3 of 4)

5. What items need to be successfully implemented to verify item S1? -- a. C1; b. D3; c. D2 & D3; d. D3, D4, & D5

6. For tracing purposes, where does item D1 come from? -- a. none of the listed items; b. S1; c. X1; d. S1 & X1

4. Homework

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Problem (4 of 4)

7. For tracing purposes, where does item U2 come from? -- a. none of the listed items; b. D5; c. D4; d. S1

8. If item D3 were to change to no longer require an AC adapter, which items would change? -- a. no items would change; b. D4; c. D4 & U1; d. D4, D5, U1, & U2

4. Homework