Laws of Computer Science and Programming

Question

We have Amdahl's law that basically states that if your program is 10% sequential you can get a maximum 10x performance boost by parallelizing your application.

Another one is Wadler's law which states that

    In any language design, the total time spent discussing
    a feature in this list is proportional to two raised to
    the power of its position.

        0. Semantics
        1. Syntax
        2. Lexical syntax
        3. Lexical syntax of comments

My question is this: What are the most important (or at least significant / funny but true / sad but true) laws of Computer Science and programming?

I want named laws, and not random theorems, So an answer should look something like

Surname's (law|theorem|conjecture|corollary...)

Please state the law in your answer, and not only a link.

Edit: The name of the law does not need to contain it's inventors surname. But I do want to know who stated (and perhaps proved) the law

Answer 1

Conway's Law: "...organizations which design systems ... are constrained to produce designs which are copies of the communication structures of these organizations."

Answer 2

Law of Demeter/Principle of Least Knowledge:

An object should only talk to its "neighbors" and not tell its neighbors how to work or invoke methods on a neighbor's neighbor.

In other words (as Wikipedia puts it): tell your dog to walk, not tell a dog's legs to walk.

Answer 3

The Pareto principle (also known as the 80-20 rule, the law of the vital few and the principle of factor sparsity) states that, for many events, roughly 80% of the effects come from 20% of the causes.

Answer 4

There are no silver bullets by Frederick P. Brooks, Jr

There is no single development, in either technology or in management technique, that by itself promises even one orderof- magnitude improvement in productivity, in reliability, in simplicity.

Answer 5

Hofstadter's Law:

It always takes longer than you expect, even when you take into account Hofstadter's Law.

Answer 6

Brook's law:

Adding manpower to a late software project makes it later.

Answer 7

Zawinski's Law

Every program attempts to expand until it can read mail. Those programs which cannot so expand are replaced by ones which can.

Answer 8

Alan Turing's proof of the insolvability of the Halting Problem

"Given a program and its input, determine whether the program will complete or run forever."

Cannot be solved in the general case with arbitrary input

Answer 9

Wirth's law states that:

Software gets slower faster than hardware gets faster.

Answer 10

Linear speedup theorem

Given any c > 0 and any Turing machine solving a problem in time f(n), there is another machine that solves the same problem in time cf(n)+n+2.

Answer 11

Little's Law (queueing theory):

The long-term average number of customers in a stable system L (known as the Offered load), is equal to the long-term average arrival rate, λ, multiplied by the long-term average time a customer spends in the system

Answer 12

Ninety-ninety rule

The first 90% of the code takes 90% of the time. The remaining 10% takes the other 90% of the time.

Attributed to Tom Cargill and popularized by Jon Bentley. Is this superseded by Hofstadter's Law?

Answer 13

Godwin's Law:

As a [StackOverflow] discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1.

Answer 14

Peter Principle:

In a Hierarchy Every Employee Tends to Rise to His Level of Incompetence.

Answer 15

Knuth's optimization principle:

We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil.

Answer 16

Not computer science or programming specifically, but certainly true:

Anything that can go wrong will go wrong.

I don't believe it's necessary to name this adage. For those few too ashamed to admit they don't know it, here is a link for you to anonymously follow to correct this gaping hole in your knowledge.

Answer 17

Asimov's three laws:

1. A robot may not injure a human being or, through inaction, allow a human being to come to harm.
2. A robot must obey orders given to it by human beings, except where such orders would conflict with the First Law.
3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

Answer 18

Gustafson's Law ameliorates the parallelism doom-and-gloom of Amdahl's Law by stating that the problem size tends to increase in time, allowing linear application-level speedups even in the face of imperfect parallelization. The linked Wikipedia article has a much better explanation than I can muster, but here's an example:

Amdahl's Law approximately suggests: “ Suppose a car is traveling between two cities 60 miles apart, and has already spent one hour traveling half the distance at 30 mph. No matter how fast you drive the last half, it is impossible to achieve 90 mph average before reaching the second city. Since it has already taken you 1 hour and you only have a distance of 60 miles total; going infinitely fast you would only achieve 60 mph. ”

Gustafson's Law approximately states: “ Suppose a car has already been traveling for some time at less than 90mph. Given enough time and distance to travel, the car's average speed can always eventually reach 90mph, no matter how long or how slowly it has already traveled. For example, if the car spent one hour at 30 mph, it could achieve this by driving at 120 mph for two additional hours, or at 150 mph for an hour, and so on.

Answer 19

The Dilbert Principle (corollary to the Peter Principle) - by Scott Adams, of course:

The most ineffective workers are systematically moved to the place where they can do the least damage: management.

Answer 20

There is my Favorite:

Murphys Law

Simplified: "Whatever can go wrong, will go wrong"

However, there is a little more to it Wikipedia

I like this more humanized version best: „If there's more than one possible outcome of a job or task, and one of those outcomes will result in disaster or an undesirable consequence, then somebody will do it that way.“

And of course Moore's law

famous interpretation: "The processing speed of computers will double every two years!"

stated similarly 1975

Again, there's more to it: Wikipedia

Answer 21

Greenspun's Tenth Rule of Programming:

Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp.

Answer 22

Linus's Law:

Given enough eyeballs, all bugs are shallow.

Answer 23

The Last Responsible Moment for decision making rule:

The key is to make decisions as late as you can responsibly wait because that is the point at which you have the most information on which to base the decision.

Answer 24

[Sorry couldn't resist]

Stackoverflow law subjective questions:

Each question marked subjective is either closed within minutes
or it collects a large amount of upvotes. (some even both).

Answer 25

Norvig's Law: Any technology that surpasses 50% penetration will never double again (in any number of months).

Answer 26

The Law of Natural Selection: "Natural selection is the process where heritable traits that make it more likely for an organism to survive long enough to reproduce become more common over successive generations of a population. It is a key mechanism of evolution."

This applies to computer systems as well, systems that support the business functions directly related to earning capital are more likely to receive funding and therefore more likely to survive budget cuts. Hence, to survive the tumultuous nature of the software development industry it is logical to concentrate on skill that support those types of applications.

Footnote: Those of us able to apply the aforementioned principal will be more likely to earn more money and thereby be in a better position to procreate. Natural Selection wins again!

;)

Answer 27

Sods Law: (A kin to Murphy)

When it goes wrong (because according to Murphy it will). It will go wrong in the worst possible way.

Answer 28

Abraham Maslow

If the only tool you have is a hammer, you treat everything like a nail.

So, programmers should learn several languages and learn how to use the strengths of each one effectively. It is no use to learn several languages if you do not respect their differences (Roberto Ierusalimschy, Programming in Lua)

Answer 29

Principle of least astonishment

In user interface design, programming language design, and ergonomics, the principle (or rule or law) of least astonishment (or surprise) states that, when two elements of an interface conflict, or are ambiguous, the behaviour should be that which will least surprise the human user or programmer at the time the conflict arises.

Answer 30

Edward V. Berard Law

Walking on water and developing software to specification are easy as long as both are frozen.

Answer 31

I do a lot of distributed programming, so one of my favorites is Segal's Law:

A man with a watch knows what time it is. A man with two watches is never sure

The application to distributed programming is that you have to either arrange things so that your whole distributed system only has one clock driving things, or you have to accept that processes/events using different clocks are going to be running asynchronous. Two clocks will drift from each other. You can't expect two separate clocks (typcially on two seperate machines) to act in lock-step.

Answer 32

Judge Dredd's Law

"I am the Law"

Answer 33

Any sufficiently advanced technology is indistinguishable from magic.

Arthur C. Clarke, Profiles of The Future, 1961 (Clarke's third law)

The only way to discover the limits of the possible is to go beyond them into the impossible.

Arthur C. Clarke, Technology and the Future (Clarke's second law)

When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.

Arthur C. Clarke, (Clarke's first law)

Answer 34

There is "Heisenberg uncertainty principle", which in general states:

In quantum physics, the Heisenberg uncertainty principle states that certain pairs of physical properties, like position and momentum, cannot both be known to arbitrary precision.

With translation to software engineering, the application of this principle is a following: You cannot test and debug you own code, since in order to achieve it you must add additional code, therefore you test not the original system.

Answer 35

Software can only ever be two of the following:

• fast
• cheap
• delivered on time

Answer 36

Zimmerman's maxim:

Anything written down in more than one place, is wrong in more than one place.

You will never have two copies of data stay the same, especially if you depend on a human to keep them the same.

Answer 37

One of my Favourites is

"One in a million is next tuesday"

Larry Osterman.

Basically it states that when dealing with computers, things happen so fast, that even something that happens very rarely, is going to happen within the next few days.

Answer 38

I like Proebstings Law:

Compiler Advances Double Computing Power Every 18 Years

research.microsoft.com/en-us/um/people/toddpro/papers/law.htm

Answer 39

The Steve Rule:

In a random sample of programmers, there will be more named Steve then there will be females.

This can be refined to a more correct and culture-agnostic version:

In a random sample of programmers, the likelihood of there being a male name with more programmers bearing that name than there are female programmers approaches 1 as the sample size increases.

Answer 40

Atwood's Law:

Any application that can be written in JavaScript, will eventually be written in JavaScript.

Answer 41

Some less well known ones:

Wheeler's law: "All problems in computer science can be solved by another level of indirection"

Berry’s law. "The best way to go infinitely fast is to produce no code at all" - i.e. If something can be computed once, then do it at compile time.

Answer 42

Not really coined as a law, but I think this quote from Eric Evans Domain-driven design is an important aspect of Brooks "no silver bullets" law:

"One way or another, creating distinctive software comes back to a stable team accumulating specialized knowledge and crunching it into a rich model. No shortcuts. No magic bullets."

Answer 43

Postel's Law, or the robustness principle:

Be liberal in what you accept, and conservative in what you send.

Not as humorous as many other ones mentioned, but quite insightful. It was, aptly, quoted in the computer networking textbook we used at uni. Apprarently this was originally mentioned in RFC-791, "Internet Protocol," by Joe Postel, September 1981.

Differently worded variants abound (see e.g. RFC-793 and RFC-1122); a common one is: "Be conservative in what you do; be liberal in what you accept from others."

Answer 44

Hanlon's razor:

"Never attribute to malice that which can be adequately explained by stupidity."

Or alternatively:

"Do not invoke conspiracy as explanation when ignorance and incompetence will suffice, as conspiracy implies intelligence."

Answer 45

Here's another one most programmers forget:

Kerckhoffs' principle of secure cryptography: A cryptosystem should be secure even if everything about the system, except the key, is public knowledge.

Answer 46

Pareto Law

The Ninety-ninety rule I read is a plagiarism of Pareto Law http://en.wikipedia.org/wiki/Pareto_principle

Answer 47

The Dilbert and Peter Principles are superceeded (or at least contested) by the Gervais principle:

Sociopaths, in their own best interests, knowingly promote over-performing losers into middle-management, groom under-performing losers into sociopaths, and leave the average bare-minimum-effort losers to fend for themselves.

See The Gervais Principle, Or The Office According to “The Office