1 System Engineers Toolbox 1 Compliance Automation, Inc. INCOSE: NM Enchantment Chapter By Cheryl Hill August 12, 2009

2 Objectives 2 To provide three tools to help you: Elicit requirements Get all the requirements Communicate better with customers and developers Reduce rework due to requirement defects

3 33 SCOPE Requirement Check List Rationale

4 Toolkit 1: Scope Scope is an iterative process Drivers and Constraints Operational Concepts Interfaces Schedule Need Authority and Responsibility Assumptions Risk Scope is an iterative process Goals and objectives Business Case or Mission Budget

5 Why Scope? Effect Of Requirements Definition Investment On Program Costs Why are you running so fast when you dont know where you are going? German proverb

6 NEED NASA – vehicle to replace shuttle NASA – make human access to space safer and cheaper

7 NEED IS –derived from a problem assessment –why we are doing something –a way to ensure we stay on track IS NOT –the product –subject to change MUST BE –in writing –available to all

8 Goals and Objectives Goals –define specific things to accomplish to meet the need Objectives –define how we will know when we get there Transport crew to and from space station Twice as safe as shuttle

9 Stakeholders Engineering Software Logistics Operations Testing Manufacturing Maintenance System Engineering Customer Reliability Developers Security Training Safety Quality Procurement

10 External Interfaces database command status command & data Your System Test Physical Power

11 Operational Concepts Maintenance Development Test and Verification Transportation Deployment Installation Integration Transition Manufacturing Training Logistics Upgrades Operations Storage Disposal Life-cycle

12 Toolkit 2: Requirement Checklist Requirement wording Ambiguities Implementation Operations

13 Good Requirements Needed Verifiable Attainable –Technically –Cost –Schedule Customer-Centered Products, p. 119 Mandatory Characteristics

14 Characteristics of Good Requirements Improving Communications One Thought Concise Simple Stated Positively Grammatically Correct Can only be understood one way Customer-Centered Products, p. 119

15 What a requirement must state Who What Connect WHO is responsible –The system –The software –The structure WHAT shall be done –operate at a power level of … –acquire data from … –withstand loads up to …

16 Use The Correct Terms Requirements are binding - Shall Facts or Declaration of Purpose - Will Goals are non-mandatory provisions - Should Dont use must

17 Avoid Ambiguous Terms etc. Maximize Sufficient User-friendly Robust High speed Including, but not limited to Minimize Adequate Easy Ultra-low power TBD Customer-Centered Products, p Indefinite pronouns - this - these - it - and/or - be able to/be capable of Accommodate Support

18 How: The aircraft shall have three engines (DC-3 initial requirements). What: The aircraft shall meet the operation requirements with a single engine out. The magic of why Implementation Versus Requirements How: The System shall include flight performance instrumentation. What: The System shall measure its flight performance. What do you want to verify?

19 Operations Statements Requirement The operator shall have the capability to change the given thread selection. Rewrite The system shall allow a change of thread selection during operations. The system shall provide a user interface for thread selection changes.

20 Toolkit 3: Rationale What How Why

21 Rationale – defines Why a requirement is needed What assumptions were made What design effort drove the requirement Information to help understand the requirement Source of any numbers

22 What NOT to Put in Rationale A rewrite of the requirement Hidden requirements Copy of another requirements rationale Everything you know on the topic

23 Rationale Benefits Key to understanding Reduce interpretation problems Facilitate maintenance and upgrades Preserve corporate knowledge

24 Example Requirement: The truck shall have a height of no more than 14 feet. Rationale: Ninety-nine percent of all U.S. interstate highway overpasses have a 14- foot or greater clearance. (Assumption: The truck will be used primarily on U.S. interstate highways for long-haul, intercity freight in the U.S.)

25 SCOPE Requirement Check List Rationale Your Tool Box