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2. Requirements 1
Agenda for understand-req activity1. Objective2. Identifying the customer3. Learning what the customer wants4. Trade studies5. Quality functional deployment (QFD)6. Validating customer requirements7. Writing requirements8. Homework
Guidelines for a good requirementNeededCapable of being verifiedFeasible schedule, cost, and
implementationAt correct level in hierarchyCannot be misunderstoodGrammatically correctDoes not duplicate information
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2. Requirements 37
Tools for writing good requirementsRequirements elicitationModelingTrade studies
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Example 1 -- good requirements
The motor shall weigh less than 10 pounds.The software shall use less than 75 percent of
the computer memory available for software.The MTBF shall be greater than 1000 hours.
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2. Requirements 39
Example 2 -- verification (1 of 3)
Customer want -- The outside wall shall be a material that requires low maintenance
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2. Requirements 40
Example 2 -- verification (2 of 3)
First possible rewording -- The outside wall shall be brick. More verifiable Limits contractor options Not a customer requirement
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2. Requirements 41
Example 2 -- verification (3 of 3)
Second possible rewording -- The outside wall shall be one that requires low maintenance. Low maintenance material is one of the following: brick, stone, concrete, stucco, aluminum, vinyl, or material of similar durability; it is not one of the following: wood, fabric, cardboard, paper or material of similar durability Uses definition to explain undefined
term
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2. Requirements 42
Example 3 -- feasible
Not feasible requirement -- The assembly shall be made of pure aluminum having a density of less than 50 pounds per cubic foot
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2. Requirements 43
Example 4 -- level
Airplane shall be capable carrying up to 2000 pounds Wing airfoil shall be of type Clark Y
Airplane
Wing
Wing airfoil shall be of type Clark Y
Wing airfoil type is generally a result of design and should appear in the lower product spec
and not in the higher product spec.
Wing airfoil type is generally a result of design and should appear in the lower product spec
and not in the higher product spec.
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2. Requirements 44
Example 5 -- understanding
Avoid imprecise terms such as Optimize Maximize Accommodate Etc. Support Adequate
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2. Requirements 45
Example 6 -- duplicationCapable of a maximum rate of 100 gpmCapable of a minimum rate of 10 gpmRun BIT while pumping 10 gallons - 100
gpmVs: Run BIT while pumping between min.
and max.
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2. Requirements 46
Example 7 -- tough requirements
BIT false alarm rate < 3 percentComputer throughput < 75 percent of capacityPerform over all altitudes and speedsConform with all local, state, and national lawsThere shall be no loss of performanceShall be safeThe display shall look the sameTBDs and TBRsStatistics
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Notes
Perfect requirements can’t always be written
It’s not possible to avoid all calamitiesRequirements and design are similar
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8. Homework (1 of 3)1. RAA for requirements in the understand-
customer activity lie with (a) requirements management, (b) the customer, (c) the contractor, (d) quality assurance
2. The understand-customer activity reaches agreement with the customer on which type of interfaces: (a) interfaces external to the product, (b) interfaces internal to the product,(c) all interfaces, (d) interfaces that constrain product development
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Homework (2 of 3)3. The customer is (a) is always one entity, (b)
may be more than one entity, (c) always the product at the next-higher level, (d) undefined
4. A good practice in reaching agreement with the customer is to have agreements made by (a) management, (b) contracts, (c) a single-point of contact for customer and a single-point of contact for contractor, (d) individual stakeholders
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Homework (3 of 3)5. Trade studies should (a) always be done,
(b) always use the method defined in the INCOSE Systems Engineering Handbook, (c) be done only if needed, (d) always include QFD considerations
6. For the requirement “Performance shall be met when speed greater than 200 mph and speed less that 400 mph,” performance must be met at (a) requirement unclear, (b) 200 mph and 400 mph, (c) any one point in the speed range, (d) all points in the speed range.