Requirements Analysis

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Requirements Analysis

• What, not How!

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Reference

• Exploring Requirements, Quality BEFORE Design, by
  Donald C. Gause Gerald M. Weinberg
• Dorset House Publishing, 1989
• ISBN 0-932633-13-7

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Its All About Reducing Ambiguity

• Consider the following requirement
• Create a means for protecting a small group of
  human beings from the hostile elements of their
  environment.
• Does this mean
• An Igloo
• A Bavarian Castle
• A Space Station

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Other Problems in This Example

• Missing Requirements
• No properties of materials specified.
• Nothing is said about physical environment.
• Little is said about functions.
• Ambiguous Words
• Small??
• Group??
• Structure?? (Actually not mentioned!!, Only
  means.) If we use the term structure we assume a
  solution!

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A Picture Of Requirements
What we want
What we dont want
The Universe of Everything Thats Possible
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Exploring Requirements
Tools
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Focus Slide
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A Problem With Direct Questions!

• When you ask questions about a requirement, you
  are building a decision tree.
• Take out a sheet of paper and number one side 1
  and the other side 2.
• On side 2 at the top of the page, put the
  following requirement

Design A Transportation Device.
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Consider The Following Question

• How many points were in the star that was used as
  a focus slide for this representation?

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Questions(number these on side 1)

1. What do you think the answer is to the question
   posed on the previous slide?

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Questions(number these on side 1)

1. What do you think the answer is to the question
   posed on the previous slide?
2. With 100 people attending the seminar, how many
   different answers did the participants write down
   as their first-impression answer to the question?

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Questions(number these on side 1)

• What do you think the answer is to the question
  posed on the previous slide?
• With 100 people attending the seminar, how many
  different answers did the participants write down
  as their first-impression answer to the question?
• What factors do you think are responsible for the
  differences among answers?

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Questions (number these on side 1)

• What do you think the answer is to the question
  posed on the previous slide?
• With 100 people attending the seminar, how many
  different answers did the participants write down
  as their first-impression answer to the question?
• What factors do you think are responsible for the
  differences among answers?
• Write down, verbatim to the best of your ability,
  the question that you think you answered in
  question 1.

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Results (clumped answers)
75
Not to scale.
12
4
3
3
2
1
8
0-2
5-9
10-12
13-16
21-24
29-32
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Discussion?

• 0 2 4
• 5 9 75
• 10 12 1
• 13 16 12
• 21 24 2
• 29 32 3
• Infinity 3

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Now!

• Does the previous discussion prompt you to change
  your answer to the number of points question?

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Now!

• Does the previous discussion prompt you to change
  your answer to the number of points question?
• In the test
• 0-2 went up to 10.
• 5-9 went down to 65.
• 13-16 went up a couple.
• Infinity went up a couple.

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Sources Of Experimental Error

• Observational and recall errors.
• Interpretation errors.
• Read some examples of the question.
• The actual question was How many points were in
  the star that was used as a focus slide for this
  representation?

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Back To Direct Questions

• On side 2, you have a requirement. What do you
  think the manufacturing cost would be for the
  solution to this requirement? (Write your first
  estimate below the requirement.)
• What are some of your estimates?
• Now, lets ask some direct questions.

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Question 1

• Designer When is the solution needed?

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Question 1

• Designer When is the solution needed?
• Client Within eighteen months.

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Question 2

• Designer When is the solution needed?
• Client Within eighteen months.
• Designer What is to be transported?

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Question 2

• Designer When is the solution needed?
• Client Within eighteen months.
• Designer What is to be transported?
• Client People.

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Question 3

• Designer When is the solution needed?
• Client Within eighteen months.
• Designer What is to be transported?
• Client People.
• Designer How many people are to be transported
  at one time?

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Question 3

• Designer When is the solution needed?
• Client Within eighteen months.
• Designer What is to be transported?
• Client People.
• Designer How many people are to be transported
  at one time?
• Client 1

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Question 4

• Designer When is the solution needed?
• Client Within eighteen months.
• Designer What is to be transported?
• Client People.
• Designer How many people are to be transported
  at one time?
• Client 1
• Designer How is the device to be powered?

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Question 4

• Designer When is the solution needed?
• Client Within eighteen months.
• Designer What is to be transported?
• Client People.
• Designer How many people are to be transported
  at one time?
• Client 1
• Designer How is the device to be powered?
• Client Only by the person being transported and
  natural forces that are readily available. It is
  to be passenger-powered.

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Question 5

• Designer Over what kind of surface or terrain is
  the device to travel?

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Question 5

• Designer Over what kind of surface or terrain is
  the device to travel?
• Client It is to provide transportation over a
  very hard, flat surface.

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Question 6

• Designer Over what kind of surface or terrain is
  the device to travel?
• Client It is to provide transportation over a
  very hard, flat surface.
• Designer How far is the person to be
  transported?

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Question 6

• Designer Over what kind of surface or terrain is
  the device to travel?
• Client It is to provide transportation over a
  very hard, flat surface.
• Designer How far is the person to be
  transported?
• Client Up to 1.2 miles.

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Question 7

• Designer Over what kind of surface or terrain is
  the device to travel?
• Client It is to provide transportation over a
  very hard, flat surface.
• Designer How far is the person to be
  transported?
• Client Up to 1.2 miles.
• Designer How fast must the device travel?

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Question 7

• Designer Over what kind of surface or terrain is
  the device to travel?
• Client It is to provide transportation over a
  very hard, flat surface.
• Designer How far is the person to be
  transported?
• Client Up to 1.2 miles.
• Designer How fast must the device travel?
• Client At least one mile every four hours.

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Question 8

• Designer How reliable must the device be?

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Question 8

• Designer How reliable must the device be?
• Client It may not have more than one failure per
  thousand miles of operation, and that failure may
  not be one that endangers the passenger.

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Question 9

• Designer How reliable must the device be?
• Client It may not have more than one failure per
  thousand miles of operation, and that failure may
  not be one that endangers the passenger.
• Designer Are there any cost limitations?

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Question 9

• Designer How reliable must the device be?
• Client It may not have more than one failure per
  thousand miles of operation, and that failure may
  not be one that endangers the passenger.
• Designer Are there any cost limitations?
• Client The device must be designed, developed,
  and manufactured so that it will cost less than
  three hundred Swiss francs each time the device
  is used.

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Estimate the manufacturing cost again.

• Add this estimate below the previous one.
• What are some of your estimates?

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Estimates From An Experiment

• First manufacturing cost estimates ranged from
  10 to 15 billion (with a b).
• Second manufacturing cost estimates ranged from
  20 to 10,000.
• There were two clusters, called Little Wheels
  and Big Wheels.
• These designers were reasonably confident that
  they had a grasp of the situation. Lets say our
  company was given the green light.

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The Solution?

• We designed and manufactured a compact,
  lightweight, folding tricycle that can be carried
  in a pedestrians hip pocket.
• Profitably sold for not more than 49.95 with a
  sales volume of 100,000 per year for 5 years.
• What a slick solution!
• ???

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Surprise!

• At a presentation, our client said, Im
  delighted with the portability of the device, but
  could you explain how it can be used to rescue a
  climber on the north face of Eiger Mountain?
• Whoops!?!
• Evidently we missed something.

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Clients Clarification

• Our clients explain, what they had in mind was a
  mountaineers rescue device, which is
  understandable since Grindelwald and Wengen base
  their economies on tourism in general and
  mountain climbing in particular. To keep tourism
  booming and to make sure climbers return, the
  villages official guides must rescue stranded
  climbers.

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Context-Free Questions

• High-level questions that can be posed early in a
  project to obtain information about global
  properties of the design problem and potential
  solutions.
• Context free questions are completely appropriate
  for any product to be designed, whether its an
  automobile, airplane, ship, house, jingle, light
  bulb, or a trek in Nepal.

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Example Context Free QuestionsAbout Process

• Who is the client for the project?
• What is a highly successful solution really worth
  to this client?
• What is the real reason for wanting to solve this
  problem?
• Should we use a single design team, or more than
  one? Who should be on the team(s)?
• How much time do we have for this project?
• What is the trade-off between time and value?

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Example Context Free QuestionsAbout Product

• What problem does this system solve?
• What problems could this system create?
• What environment is this system likely to
  encounter?
• What kind of precision is required or desired in
  the product?

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Example Metaquestions

• Am I asking you too many questions?
• Do my questions seem relevant?
• Are you the right person to answer these
  questions? Are your answers official?
• (The accounts payable story reprise.)
• Is there anyone else who can give me useful
  answers?
• Is there someplace I can go to see the
  environment in which this product will be used?

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Example Metaquestions (cont.)

• Is there anything else I should be asking you?
• Is there anything you want to ask me?
• May I return or call you with more questions
  later, in case I dont cover everything this time?

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Mary Had A Little Lamb Heuristic

• Take a statement and emphasize each word one by
  one, and then in combinations.
• Mary had a little lamb.
• (It was marys lamb, not Toms or Sams.)
• Mary had a little lamb.
• (She no longer has the lamb.)
• Mary had a little lamb.
• (She no longer has the lamb.)

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(cont.)

• Mary had a little lamb.
• (It really was surprisingly small.)
• Mary had a little lamb.
• (She didnt have a dog, cat, goat, or bird.)
• Mary had a little lamb.
• (John still has his little lamb.)
• Mary had a little lamb.
• (As contrasted witih Pallas, who still has four
  large turtles.)

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Importance Of the Projects Name

• The right name increases possibilities.
• The wrong name stifles possibilities.
• One word is worth a thousand pictures.
• The Naming Heuristic
• Propose a name.
• Offer three reasons why the name is NOT adequate.
• Propose another name that eliminates these
  problems.
• Dont go on forever!

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Determining If It Is A Function

• Take the phrase you are proposing and add We
  want the product to in front of it.
• E.G. Display Current Floor
• We want the Elevator Information System to
  Display Current Floor.
• E.G. Purple
• We want the Elevator Information System to
  purple.

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EHF Designation

• E Evident
• Function that is visible to users.
• H Hidden
• Function that must be as imperceptible to users
  as possible.
• F Frill
• Function that the client would like, but not if
  they cost anything.

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Qualities Of Requirements

• (from Pfleeger)
• Correct?
• Consistent?
• Complete?
• Realistic?
• Needed?
• Verifiable?
• Traceable?
• Legal?

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Requirements Validation Checklist

• (from Pressman)
• Are requirements stated clearly? Can they be
  misinterpreted?
• Is the source of the requirement identified?
• Is the requirement bounded in quantitative terms?
• What other requirements relate to this
  requirement? Cross reference?

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Requirements Validation Checklist

• (from Pressman) (cont.)
• Does the requirement violate any system domain
  constraints?
• Is the requirement testable?
• Is the requirement traceable to any system model
  that has been created?
• Is the requirement traceable to overall
  system/product objectives?

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Requirements Validation Checklist

• (from Pressman) (cont.)
• Is the specification structured in a way that
  leads to easy understanding, easy reference, and
  easy translation into more technical work
  products? (classes, functions, . Code)
• Has an index for the specification been created?
• Have requirements associated with performance
  behavior, and operational characteristics been
  clearly stated?
• What requirements appear to be implicit?

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Requirement versus Specification

• Requirements are more loosely stated and readable
  by customer.
• Specifications are more precise and designed for
  reading by developer.
• I like to do requirements in English precisely
  and without jargon so they support both customers
  and developers.
• The response time will be fast story, if time
  permits.