Software Is Details @KevlinHenney Any program is a model of a - - PowerPoint PPT Presentation

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Software Is Details @KevlinHenney Any program is a model of a - - PowerPoint PPT Presentation

Jan 18, 2023 473 likes •1.24k views

Software Is Details @KevlinHenney Any program is a model of a model within a theory of a model of an abstraction of some portion of the world or of some universe of discourse. Meir M Lehman "Programs, Life Cycles, and Laws of Software

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Software

Is Details

@KevlinHenney

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Any program is a model of a model within a theory of a model

  • f an abstraction of some portion
  • f the world or of some universe
  • f discourse.

Meir M Lehman

"Programs, Life Cycles, and Laws of Software Evolution"
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The purpose of abstraction is not to be vague, but to create a new semantic level in which one can be absolutely precise.

Edsger W Dijkstra

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It's just semantics.

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It's just meaning.

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It's just details.

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Details count.

Peter Weinberger

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Geeks are people who love something so much that all the details matter.

Marissa Mayer

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We're talking about a very specific mindset that is crucial when it comes to the act of creating.

Will Gompertz Think Like an Artist

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It is an attitude that can be encapsulated in a simple but demanding rule: always think both big picture and fine detail.

Will Gompertz Think Like an Artist

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software

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software architecture

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code

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implementation

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implementation details

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design details

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design decisions

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Architecture represents the significant design decisions that shape a system, where significant is measured by cost of change.

Grady Booch

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Architecture is a hypothesis, that needs to be proven by implementation and measurement.

Tom Gilb

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We propose [...] that one begins with a list of difficult design decisions or design decisions which are likely to change. Each module is then designed to hide such a decision from the others.

David L Parnas

On the Criteria to Be Used in Decomposing Systems into Modules
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Programming is a design activity.

Jack W Reeves

What Is Software Design?
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Coding actually makes sense more often than believed. Often the process of rendering the design in code will reveal

  • versights and the need for additional

design effort. The earlier this occurs, the better the design will be.

Jack W Reeves

What Is Software Design?
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If a plot works out exactly as you first planned, you're not working loosely enough to give room to your imagination and instincts.

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/ WordFriday

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pantser, noun

  • Writer who writes by the seat of their pants.
  • In contrast to a plotter, a pantser doesn't

work to (or have) an outline.

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16-bit

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32-bit

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64-bit

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<windows.h>

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LLP64

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LP64

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Hamlet: To be, or not to be, that is the question.

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Ophelia: 'Tis in my memory locked, and you yourself shall keep the key of it.

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Hamlet: Yea, from the table

  • f my memory I'll wipe

away all trivial fond records.

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Mutable Immutable Unshared Shared

Unshared mutable data needs no synchronisation Unshared immutable data needs no synchronisation Shared mutable data needs synchronisation Shared immutable data needs no synchronisation

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Mutable Immutable Unshared Shared

Unshared mutable data needs no synchronisation Unshared immutable data needs no synchronisation Shared mutable data needs synchronisation Shared immutable data needs no synchronisation

The Synchronisation Quadrant

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All computers wait at the same speed

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Savings in time feel like simplicity

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... premature optimization is the root of all evil (or at least most of it) in programming.

Donald Knuth

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... premature optimization is the root of all evil (or at least most of it) in programming.

Donald Knuth

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... premature optimization is the root of all evil (or at least most of it) in programming.

Donald Knuth

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Command-line tools can be 235x faster than your Hadoop cluster

Adam Drake http://aadrake.com/command-line-tools-can-be-235x-faster-than-your-hadoop-cluster.html
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sort

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O(n log n)

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O(n2)

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O(n!)

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OMG!

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O(n)

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Simple Testing Can Prevent Most Critical Failures

An Analysis of Production Failures in Distributed Data-Intensive Systems

https://www.usenix.org/system/files/conference/osdi14/osdi14-paper-yuan.pdf
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Schiaparelli’s Inertial Measurement Unit (IMU) went about its business of calculating the lander’s rotation

  • rate. For some reason, the IMU calculated a saturation-

maximum period that persisted for one second longer than what would normally be expected at this stage. When the IMU sent this bogus information to the craft’s navigation system, it calculated a negative altitude.

http://gizmodo.com/a-crazy-miscalculation-doomed-the-sciaparelli-lander-1789319670
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That fateful miscalculation set off a cascade of despair, triggering the premature release of the parachute and the backshell, a brief firing of the braking thrusters, and activation of the on-ground systems as if Schiaparelli had already reached the surface. This all happened while the vehicle was still two miles (3.7 km) above ground.

http://gizmodo.com/a-crazy-miscalculation-doomed-the-sciaparelli-lander-1789319670
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A majority of the production failures (77%) can be reproduced by a unit test.

https://www.usenix.org/system/files/conference/osdi14/osdi14-paper-yuan.pdf
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SLIDE 69 http://www.commitstrip.com/en/2016/08/25/a-very-comprehensive-and-precise-spec/
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SLIDE 70 http://www.commitstrip.com/en/2016/08/25/a-very-comprehensive-and-precise-spec/
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SLIDE 71 http://www.commitstrip.com/en/2016/08/25/a-very-comprehensive-and-precise-spec/
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SLIDE 72 http://www.commitstrip.com/en/2016/08/25/a-very-comprehensive-and-precise-spec/
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Normally screws are so cheap and small and simple you think of them as unimportant. But now, as your Quality awareness becomes stronger, you realize that this one, individual, particular screw is neither cheap nor small nor unimportant.

Robert M Pirsig

Zen and the Art of Motorcycle Maintenance
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Right now this screw is worth exactly the selling price of the whole motorcycle, because the motorcycle is actually valueless until you get the screw out. With this reevaluation of the screw comes a willingness to expand your knowledge of it.

Robert M Pirsig

Zen and the Art of Motorcycle Maintenance
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Software

Is Details