Transcript EENG 1920 Ch 3x

EENG1920 Chapter 3
The Requirements Specification
1
Requirements Specification
• Engineering Requirement
• Marketing Requirement
• Requirements Specification
2
Engineering & Performance Requirements
• Engineering requirements
– Requirements that are concerned with the
technical aspects of the design (voltage,
amperes, etc.).
• Performance requirements
– A subset of the engineering requirements
– Limited in scope and specify performance
related issues (speed, refresh rates, etc).
3
System & Subsystem Specifications
• System requirements specifications
– General specifications that apply to the entire
project or system.
• Subsystem design specification
– A smaller more defined portion of a complex
system.
4
Engineering Requirement Properties
1.
2.
3.
4.
5.
Abstract
Verifiable
Unambiguous
Traceable
Realistic
– technically feasible.
5
Constraints
• Design decision impacts or limits the design.
• Example: The system must use a PIC18F52
microcontroller to implement processing functions.
6
Standards
• A standard is what?
• What standards are relevant to your
project and how do you use them?
• Types: safety, testing, reliability,
communication, data, documentation,
design
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•
•
•
•
•
•
Structured workshops and brainstorming
Interviews and surveys
Observation of processes and devices in use
Benchmarking and market analysis
Prototyping and simulation
Research survey
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• Need to know what type of requirement to
select for a given system.
• These are but EXAMPLES – you must
determine the correct ones for your
system!
• Hint: don’t just try to copy and paste them.
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Performance
• The system shall detect 90% of all human faces
in an image.
• The amplifier shall have a total harmonic
distortion less than 1%.
Reliability & Availability
• The system shall have a reliability of 95% in five
years.
• The system shall be operational from 4AM to
10PM, 365 days a year.
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Energy
• The system shall operate for a minimum of three
hours without needing ……….
Environmental
• The system shall be able to operate in the
temperature range of 0°C to 75°C.
• The system shall be waterproof and operate
while submersed in water.
• The system shall be rechargeable.
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Validation &Verification
• Validation
– The process of determining if the requirements meet
the needs of the end-user.
– Answers the question – are we building the right
product?
• Verification
– The process of measuring or demonstrating that the
requirements are met.
– Answers the question – are we building the product
right (does it meet the requirements).
– Harder to determine
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How Do You Validate Requirements
• Is each requirement verifiable?
– Can it be measured or shown in the final
system implementation.
• Is each requirement traceable to a user
requirement?
• Is each requirement realistic and
technically feasible?
– This may be hard to determine.
– Can it determined in the system prototype.
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How Do You Validate Requirements
• Are the requirements established with no
redundancy?
• Is the property of completeness met?
– Are all the needs of the end-user addressed
in the Requirements Specification?
• Is the property of consistency met?
– The Requirements Specification should not be
self-contradictory.
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Marketing Requirement
1. The system should have excellent sound
quality.
2. The system should have high output power.
3. The system should be easy to install.
4. The system should have low cost.
5. Should be able to fit and operate in an
automobile.
6. Should be easy to use.
7. Should be portable.
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Car Audio Amplifier
Marketing
Requiremen
Engineering Requirements
ts
1, 2, 4
1. The total harmonic distortion
should be <0.1%.
1–4
2, 4
3
Justification
Based
upon
competitive
benchmarking
and
existing
amplifier technology. Class A, B,
and AB amplifiers are able to obtain
this level of THD.
1. Should be able to sustain an This power range provides more
output power that averages  than adequate sound throughout
35 watts with a peak value
the automobile compartment. It is a
sustainable output power for
of  70 watts.
projected amplifier complexity.
1. Should have an efficiency () Achievable with several different
>40 %.
classes of power amplifiers.
1. Average installation time for
Past trials using standard audio and
the power and audio
power jacks demonstrate that this is
connections should not
a reasonable installation time.
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exceed 5 minutes.
Car Audio Amplifier
1–4
1. The dimensions should Fits under a typical car seat.
not exceed 6” x 8”x 3”. Prior models and estimates
show that all components
should fit within this
package size.
1–4
1. Production cost should This
is
based
upon
not exceed $100.
competitive market analysis
and
previous
system
designs.
Marketing Requirements
1.The system should have excellent sound quality.
2.The system should have high output power.
3.The system should be easy to install.
4.The system should have low cost.
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Requirements Analysis
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1) Sound Quality
+
2) High Power
+
3) Install Ease
+
4) Cost
-
+
+
-
-
Cost
Dimensions
Install Time
, Efficiency
Output Power
THD
-
-
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THD
Output Power
, Efficiency
Install Time
Dimensions
Cost
THD
Output Power
, Efficiency
Install Time
Dimensions
Cost
-
+
+
-
-
-
+
+
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Apex Audio Monster Amps
Our Design
THD
0.05%
0.15%
0.1%
Power
30W
50W
35W
Efficiency
70%
30%
40%
Cost
$250
$120
$100
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Summary
• Requirements Specification.
– marketing requirements
– engineering requirements
• Should be abstract, verifiable, and traceable
• Some constraints
• Some standards
– Advanced analysis
• Marketing tradeoffs
• Engineering tradeoffs
• Benchmarks
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Chapter 3 Homework
1.
2.
3.
4.
5.
6.
7.
Name the three requirements needed for a Specification.
Define engineering requirements.
Define performance requirements.
What are system requirements specifications?
What are subsystem design specification?
What is validation?
What is Verification?
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