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Chapter 3

From Chapter 2 we had these “steps” in the SE process:

• Problem definition• Consumer need• Feasibility• System operational

requirements• Maintenance and

support concepts• Determine/prioritize

TPMs

• Functional analysis

• Requirements allocation

• System synthesis

• Design integration

• T&E

• Production

• Operational use

• Retirement

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Chapter 3

From SE Fundamentals

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Chapter 3

• Notice how the steps on previous slide map into Fig 3.1 and Fig 1.12.

• In Fig 3.2 the MIL-STD-490 terms are used.– Type A, B etc.

– Names aren’t important the ideas of flowdown and increasing design detail are!

– We’ll use the “490” terminology but understand the meaning behind the type.

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Chapter 3 • Type A (system spec) - usually only 1.

– Technical, performance, operational and support characteristics of the system as whole.

– Feasibility,operational requirements, functional analysis products go here.

– Defines subsystems.– Has a Section 4!

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Chapter 3 • Type B (development spec) - usually

several.– Technical, performance, operational and

support characteristics of specific subsystems.– Performance, effectiveness, and support

characteristics are included.– Defines assemblies or CSCIs.– Has a Section 4!

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Chapter 3 • Type C (product spec) - usually many.

– Design details.– Hardware separate from software.– Has a Section 4!

• Type D and E– Specific process and material requirements.

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Chapter 3

From SE Fundamentals

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Chapter 3 • The requirement allocation process selects

assignments of specific allocated requirements to specific specifications.

• See Fig 3.3 for an example of a spec “tree”.– Order of precedence is important!

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Chapter 3

From SE Fundamentals

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Chapter 3

From SE Fundamentals

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Chapter 3

• See Fig 3.4.– Type A, – TPMs usually here.– These are the typically used sections.– The essence is the important part but, using this

format is comfortable within DOD.– Types B, C etc are typically laid-out the same.

• Next page from SEF Guide.

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Chapter 3

From SE Fundamentals

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Chapter 3

From SE Fundamentals

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Chapter 3

• software development

• reliability

• maintainability

• human factors

• safety

• security

• producibility

• logistics

• disposability

• quality

• environmental

• value/cost

Blanchard selects 12 design disciplines for further discussion because they have been historically inadequately integrated into system developments and mainstream design effort. They are:

We’ll discuss them briefly, be sure to be aware of the existence of them all and the type of engineering they accomplish!

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Chapter 3 • Software engineering things to know:

– Same processes and flow in the system engineering of software as hardware.

• Software engineers may have their own special names but they are equivalent.

– Testing subroutines, subprograms and integration into programs flows in a similar fashion as hardware.

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Chapter 3 • Software engineering things to know:

– Verification can include evaluating the consequences of every data path regardless of it’s use likelihood.

– Stress testing explores the limits of i/o, throughput and processing.

– Software QC deals with subjects like - were the standards followed?

– Following three charts are examples of software development methodologies...

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User Requirements Analysis

User Requirements Specifications

Software Requirements Specification

System/Broad Design Logical Design

Implementation/Coding

Program Testing: System

Program/Detailed Design Physical Design

Program Testing: Units

Program Use

Software Maintenance

Structured Analysis, Structured Design

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Requirements Analysis

Design 1

Implement 1

Design 2

Implement 2

Design 3

Implement 3

Test Planning Certification 1

Certification 2 Certification 3

Cleanroom Design

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Object Oriented Design

Effort Implementation

Detailed Design

Broad Design

Software requirements

Requirements analysis

Time

Basic Classes Specific Classes

I disagree with the author’s note 12 page 127. Objects are determined by the functional flowdown.

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Chapter 3 • Reliability Engineering things to know:

– Probability based.– Item is considered reliable if the mission of the

device is accomplished.• Implies a component may fail it’s mission while the

system may not fail it’s mission and vice versa• R, MTBF and are important parameters.• R= e-t where t = operating time and = average failure

rate.• e-t represents the probability of zero failures in t.

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Chapter 3 • Reliability Engineering things to know:

– Look at the typical failure curves in Fig 3.8.– What’s the difference between a software

failure and a hardware failure?– Note the effects of redundancy on reliability in

Fig 3.11.– In Fig 3.14 items 1-5 are for SE’s, and 17-20

for testers (also SE’s).

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Chapter 3 • Reliability Engineering things to know:

– Importance of FRACAS!• Suggest an automated problem identification and

notification system!– Anyone who suspects a problem documents it and then it gets

dispositioned (i.e. reviewed and actions assigned to correct as required).

– Let’s look at the reliability qualification testing paragraph page 142, para7

• Notice the synergism that can/should occur– Results in time and $ savings

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Chapter 3 • Maintainability Engineering things to know:

– Maintainability is the ability of an item to be maintained.

– Maintenance is the action to restore or retain a specified operating condition.

– See the time relationships in Fig 3.17.– A log-normal distribution is typical of

maintenance times. See Fig 3.18.

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Chapter 3 • Maintainability Engineering things to know:

– See Fig 3.19. How many were false alarms?– Availability is the factor of interest to your customer.

• A = MTBM/(MTBM + MDT)

– If one has or anticipates low A what’s the fix?• Lots of units, Lots of spares, Lots of maintenance personnel,

Lots of $$$$!

– Maintainability demonstrations are valuable but extremely expensive (See page 156)

• Look for alternative ways to get the data.

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Chapter 3 • Human factors engineering things to know:

– Human as a part of the system!

– Called ergonomics, considers:• Size (page 159).

• Senses.

• Physiological factors.

• Psychological factors.

• Interface called MMI.

• This interface requires as much or more definition as machine to machine. This can be a big time consumer.

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Chapter 3 • Human factors engineering things to know:

– Mockups and simulators likely required during design.

– Human subjects typical of end user (I.Q., training, etc.) needed as test subjects during design.

– See Fig 3.26 for tasks especially #15- testing.

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Chapter 3 • Safety engineering things to know:

– This is not about conducting a test safely.– This is about designing a system to minimize

human and hardware/software exposure to unsafe conditions.

– When a hazard can’t be eliminated then safety engineering determines a safe (acceptable risk) way to deal with it.

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Chapter 3 • Safety engineering things to know:

– Notice how many of the “ilities” come together synergistically (integrated by the SEMP) to support safety.

• Paragraph 1 section 3.4.5 page 167.

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Chapter 3 • Security engineering things to know:

– Prevents planned introduction of faults/failures.– Similar to preventing inadvertent faults by

careless operators… except for intent.– Includes encryption techniques and devices.– Virus detectors and physical access barriers are

examples.

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Chapter 3

– critical materials

– critical processes

– proprietary items

– special production tooling

– unrealistic tolerances

– special test systems

– highly skilled personnel

– production/procurement lead times

•Producibility engineering things to know:•Objective is to convert the results of R&D efforts into something that can be produced outside the lab.•Minimize the following:

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Chapter 3 • Logistics engineering things to know:

– Figure 3.32 is a good summary of the elements of logistics.

– Figure 3.33 shows when engineering can influence the design to reduce risk and costs.

– Logistics is an area with tremendous lifetime costs !

– OT&E is the typical place for evaluation of the logistics “stream”.

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Chapter 3 • Quality engineering things to know:

– QC and QA are after the fact i.e. checking the final product.

– TQM and QFD are from the beginning.– Emphasis on the following:

• Customer satisfaction – no satisfaction – no quality.• Continuous improvement.• Variability minimization (6 sigma).• Everyone (not just an inspector) involved.

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Chapter 3 • Environmental engineering things to know:

– Ecological, political and social factors.– Affects test choices e.g.:

• Bombing range in Puerto Rico.• Sonar test impact on whales.

– Use and retirement issues.• Lithium batteries in airplanes.• Nuclear “leftovers” like old submarine reactors -

where do you dispose of them?

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Chapter 3 • Value/Cost engineering things to know:

– See top of page 188 for examples of “figures of merit”.

– From a functional flow diagram, estimate the costs of the various functions from beginning to end.

• Lots of models exist.

– Appendix B provides details and examples.– LCC analysis may justify expensive testing.