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1
System Engineer’s Toolbox
1
Compliance Automation, Inc.
INCOSE: NM Enchantment ChapterBy
Cheryl HillAugust 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
333
SCOPE
Requirement Check List
Rationale
4
Toolkit 1: Scope
Scope is an iterative process Drivers and
Constraints
Operational Concepts
InterfacesSchedule
Need
Authority and Responsibility
Assumptions
Risk
Scope isan iterative
process
Goals and objectives
Business Caseor Mission
Budget
5
Why Scope?Effect Of Requirements Definition Investment On Program Costs
20
80
60
40
160
140
120
100
200
180
5 10 15 20 25 30
OMV
GRO 78
GALL
TDRSS
CENHST
EUVE/EP
GOES I-M
ACT
MARS
MAG
SEASATUARS
DESMM
ERB 77
LAND 76
IRAS
TETH
STS LAND 78
GRO 82
ERB 80
VOYAGER
ULYSSES
PION/VENIUE
ISEE
COBE
HEA
Target Total Cost
Requirements Definition and Preliminary Design
Tar
get
Co
stA
ctu
al –
Tar
get
Co
st
Why are you running so fast when you don’t 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
SystemEngineering
Customer
ReliabilityDevelopers
Security
Training
Safety
Quality
Procurement
10
External Interfaces
database
com
man
d
stat
uscommand & data
Your System
Test
Physical
Power
11
Operational Concepts
Maintenance
Development
Test and Verification
Transportation
Deployment
Installation
Integration
TransitionManufacturing 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
• Don’t 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. 162-4
• 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 requirement’s 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