Requirements: Definition

1. EMIS 8340 Systems Engineering Tool—applying tools to engineering systems Requirements: Definition Mark E. Sampson

2. Requirements Definition • Once we get all of these requirements captured, now what? • Analyze • Prioritize • Organize …the process of getting to the most important requirements (…all requirements are not created equal)

3. Requirements Analysis…Requirement Parsers Automatically looking for requirements… • Structure parsers—most conservative approach • Key-Word parsers—assumes customer wrote the requirements for you • Boolean parsers—is req if shall | will AND be !-maybe • Context parsers—automatic syntactic and semantic analysis …lots of ongoing researchin this area… • Automatic news feeds • Indexers • Pattern-matching • Semantic Parsers

4. Requirements Analysis…Rationale Capture • Why? The rationale behind the requirement… • Why record rationale? • reduces requirement count…you have to justify them • exposes bad assumptions • exposes implementation/pre-selection error • improves communication among stakeholders • shortens/eliminates reviews • captures/maintains corporate/tribal knowledge …liver & onions Implementation …an all-metal, trimotor monoplane of maximum Gross of 14,200 pounds, fuel capacity for cruising 1000 miles at 150 mph with at least 12 passengers and crew of two… TransContinental Air Requirement 1932 [Hooks 2001]

5. Requirements Analysis…Rationale continued… • What should rationale include • Reasoning • Assumptions • Design choices • When? When you make decisions, not later. Later never comes. • Where? Associated directly with requirements…so its right with the requirement Example: Requirement: Height shall not exceed 14 ft. Reason: 99% of interstate highway bridges are greater than 14 ft. Design Choices: Standard steel sheeting materials is 12 ft. Cost of custom material size is prohibitive to go wider. Aluminum sheeting is available in 14 ft sheet from Alcoa. [Hooks 2001]

6. Requirements Definition…Requirement Prioritization • Some requirements are more important than others. • Helps you understand your options as things change • Enables you to deliver a useful product as things fall overboard • Foundation for architectural trades (what can be postponed…) ...how do you identify which are the most important requirements? • Define a scale—1 (critical), 2 (general), 3 (nice to have)… • Rate/Classify the requirements with stakeholders • Reconcile differences [Hooks 2001]

7. Requirements Definition…Prioritization continued… • Kano Analysis… …allows you to prioritize customer requirements based on their impact on customer satisfaction 4-types of customer needs: • Surprise/delight factors—make the product stand out; i.e. active noise suppression • More is better—i.e. better fueleconomy • Must be—without these you can’tsell the product; i.e. a car thatcan’t meet emissions standards • Dissatisfiers—cause the customernot to like the product; i.e. uncomfortable to sit in [www.isixsigma.com]

8. Requirements Definition…Prioritization continued… • Kano Analysis…continued The process: • Organize requirements into survey form for stakeholders to find out what kind of requirements they are… • Focus on moving the product to the upper-right quadrant Product should: • Meet as many of the “must be” features as possible • Add attractive criteria to put you above the competition Satisfiers —requirements which create satisfaction when presentbut experiences no dissatisfaction when it is not present One-Dimensional —requirements which result in rising satisfaction the more they are fulfilled, but lead to increasing dissatisfaction when less fulfilled. Must be’s —requirements which do not lead to satisfactionwhen fulfilled, but cause dissatisfaction when not fulfilled [www.isixsigma.com]

9. QFD—House of Quality What is QFD—method for linking voice of customer to approach to implementation by… • Capturing the voice of the customer (VOC) • Inter-relating what needs to be done with how to do it. • Drives out key requirements for addressing those needs Statistical Design Institute… Statistical Design Toolkit for Design for Six Sigma, includes a QFD tool. Introduction/Demonstration by Statistical-Design Institute

10. Requirements Definition…Prioritization continued… • Decision Trees…a way of organizing all items relevent to a decision • A number of approaches… A probabilistic approach… • Start with decision • Add all possible solutions • Add options for each solution • Add outcome probabilities &calculate Tools…Excel (Precision Tree,CrystalBall, Treeage, Visio,…) [Winston & Albright 2000]

11. Requirements Definition…Prioritization continued… • Decision Trees…continued… A pair-wise approach for prioritizingrequirements… • Start with requirements • Organized appropriately • Add solutions as leafs • Pair-wise compare each option • Rollup Results: 75% of requirements best met by PC 25% of requirements best met by Unix [Sampson 1996]

12. Requirements Definition…Prioritization continued… • Decision Trees… • Sensitivity Analysis… Results: 75% of requirements best met by PC 25% of requirements best met by Unix How sensitive is the result? • Removing user issues (Freedom) resulted in 70% PC, 30% Unix Workstation tilt • Removing management concerns (ROI, using existing assets, etc.) resulted in a 60% PC, 40% Unix tilt • With both management & user issues removed from the decision tree, the results are 50% PC, 50% Unix—i.e. either PC or Unix based solution would meetCustomer requirements equally [Sampson 1996]