5. Design1 Agenda for design activity r1. Tracing requirements r2. Managing requirements r3. Requirements management tools r4. Homework.

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


5. Design 3

Types of tracing (1 of 2)

Req

Req Req Req

Req ReqReq

Req

Straight through

Expansion Focus Creation End

DesignDesign Design Design Design

Req

Req

Five types of tracingFive types of tracing


5. Design 4

Types of tracing (2 of 2)

Weight

Weight A Weight B

Spreadsheet

Calculation GraphingNo hazardous material

Straight through

Expansion

Focus Creation

End

DesignDesign

Design Design

Bedroom on east side

Instrumentation

Design

No hazardous material

Building supplies

Missile

An example of each typeAn example of each type

5. Design 5

Complexity of tracing (1 of 2)

Spec

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


5. Design 6

Complexity of tracing (2 of 2)

Spec contract

Stakeholders

Design

Spec contract

Stakeholders

Design

Speccontract

Stakeholders

Design

I/F

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

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


5. Design 7

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


5. Design 8


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


5. Design 9


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

creates requirements


5. Design 10


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


5. Design 11


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


5. Design 12

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


5. Design 13


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


5. Design 14


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


5. Design 15


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


5. Design 16

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


5. Design 17

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


5. Design 18

Suggestion (3 of 3)

Req

Req Req Req

Req Req

ExpansionFocusDesign Design

Req

Req Req Req

Req Req

Expansion Focus

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

5. Design 19

2. Managing requirements

Requirements attributesData interface attributesPhysical interface attributesDocumenting requirementsManaging requirements change


5. Design 20

Requirements attributes (1 of 2)

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

toolProduct unique identifier (PUI) -- added by

engineersVerification method -- how requirement

verified


5. Design 21

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


5. Design 22

Data interface attributes

Data itemCriteriaTimingUnits and enumerationFormatRangesAccuracy


5. Design 23

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


5. Design 24

Physical interface attributes (2 of 2)

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


5. Design 25

Documenting requirements

Media• Paper• Office computer tools• Data base

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


5. Design 26

Managing requirements change

Often handled through configuration management

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


5. Design 27

3. Requirements management tools

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


5. Design 28

INCOSE tools survey

Comparison made by National Council on Systems Engineering (INCOSE)

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


5. Design 29

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


5. Design 30

INCOSE tool-selection criteria (2 of 2)

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


5. Design 31

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


5. Design 32

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


5. Design 33

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


5. Design 34

Considerations for compatibility

Computer and operating system being used on the project

Way team members work


5. Design 35

Considerations for satisfaction

Gain understanding of the tool before committing to use tool

Avoid choices based on demo by sales person


5. Design 36

4. Homework

DiagramCustomer wantsTimepiece specTimepiece contractDesignClock specAC adapter specProblem

4. Homework

5. Design 37

Diagram

Customer wantsC1, C2, C3

Timepiece specS1

Timepiece contractX1

Timepiece designD1, D2, D3, D4, D5

Clock specT1

Adapter specU1, U2

4. Homework

5. Design 38

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

5. Design 39

Timepiece spec

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

4. Homework

5. Design 40

Timepiece contract

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

4. Homework

5. Design 41

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

5. Design 42

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

5. Design 43

Clock spec

T1: Clock shall be a Dilmore model 100 clock

4. Homework

5. Design 44

AC adapter spec

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

U2: AC adapter shall be beige

4. Homework

5. Design 45

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

5. Design 46

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

5. Design 47

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

5. Design 48

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