slides

1. Introduction

Important questions

  • How do you know when a design is good enough?

  • What makes a design able to be called a success?

These questions demand (require) some sort of basis for making these judgements or there would be no way for any one to agree on the answers!

Requirements represent the link between understanding stakeholder (customer) needs and potential value creation and the task of technical design and implementation. They describe, both high-level and specific terms, the characteristics a system must have to be considered a successful design. Clarifying features and behaviors also promotes disciplined thinking and decision making when handling the details of a design. Making the connection between Needs and Details is what makes a design valuable for all of the people involved.

2. Reading

Begin your consideration of video United Launch Alliance: Re-designing Santa’s Sleigh

How did they start out with this task?

  • Extract and set requirements

  • State assumptions explicitly

[QRA-requirements]

[SEBoK-requirements]

Systems Engineering Book of Knowledge

Requirement vs. Implementation | What vs. How

  • One thought

  • Concise

  • Positive statement

  • Unambiguous

  • Verifiable. Inspection, analysis, demonstration, or test.

Terminology

  • Shall - requirement

  • Will - facts or declaration of purpose

  • Should - goal

  • *ize and *ly

Minimize use of

  • all

  • any

  • each

  • every

  • intent

  • it

  • these

  • this

BEFORE writing requirements

  • Define: need, goals, and objectives

  • Identify all stakeholders

  • Identify drivers, constraints, dependencies

  • Document assumptions

Eliciting requirements

  • Operational concepts. A day in the life…​

  • User stories

  • Give each requirement a unique identifier (QRA 3). This makes referring to other requirements simple and clear.

  • Standardize your requirements document language (QRA 4). Shall, must, will

2.1. Functional vs. non-functional

Functional

What the system does. Use form “The [device] shall [verb] …​”
Non-functional

Performance or constraints. Use “must”

2.2. Implementation-neutral

  • Clearly states what the system must do and not how it does it.

  • Stated in terms of external interfaces, or behaviors that can be readily observed (therefore measured).

2.3. Verifiable

How can this requirement item be satisfied?

2.4. Directives

Use of Tables or other references instead of embedding in English sentences.

3.2.5.4 Emergency Lighting
The CTS shall provide automatically activated emergency lighting for crew egress and operational recovery in accordance with Table 3.2.5.4-1. [R.CTS.044]

2.5. Weak words

  • about,

  • acceptable,

  • accommodate,

  • adequate,

  • “and/or”,

  • appropriate,

  • as allowed,

  • as directed,

  • be able to,

  • compatible,

  • desirable,

  • durable,

  • easy,

  • effective,

  • efficient,

  • enhance,

  • essential,

  • optimum,

  • possible,

  • practical,

  • reasonable,

  • relevant,

  • reliable,

  • robust,

  • significant,

  • heavy duty,

  • hereinafter,

  • high,

  • if possible,

  • dependable,

  • industrial grade,

  • insufficient,

  • intent,

  • low,

  • maximize,

  • minimize,

  • necessary,

  • normal,

  • powerful,

  • smooth,

  • strict,

  • sufficient,

  • suitable,

  • user friendly,

  • various,

3. During class

"Requirements Bingo"

3.1. R1

The Crew Transport System (CTS) needs to provide continuous autonomous launch abort capability from lift-off through orbital insertion with a 95% probability of success with at least 90% confidence in the event of a loss of thrust or loss of attitude control.

3.2. R2

No hot surfaces should be present on the outside surface of the heater.

3.3. R3

The wheelchair must support one person’s weight and, when folded, must easily fit in the trunk of a car.

3.4. R4

The motorcycle gas mileage must be at least 60 mpg.

3.5. R5

The device shall not disturb any object with a mass greater than 2 kg.

3.6. R6

The robot must not come within 10 inches of the wall.

3.7. R7

The self-contained bin on the device shall have a volume around 125 L.

3.8. R8

The software interface should be user friendly and use the Terasic display.

3.9. R9

The device shall not consume more than 500 W average power in normal running state, measured over a time interval of one second.

3.10. R10

In normal running state, the device shall generate less noise than a running car.

3.11. R11

No external surface of the device shall exceed 25 degrees Celsius in temperature otherwise the system should use a fan to reduce its temperature.

3.12. R12

The suit shall accommodate crew metabolic loads provided in Appendix F - Metabolic Loads during all flight phases while maintaining a good core body temperature.

3.13. R13

The spacecraft shall be enhanced to protect the crew from any impact force.

3.14. R14

The device shall be powered by 120VAC electricity.

References