Painless Functional Specifications

Painless Functional Specifications – Part 1: Why Bother?

By Joel Spolsky
Monday, October 02, 2000

When The Joel Test
first appeared, one of the biggest sore points readers reported had to
do with writing specs. It seems that specs are like flossing: everybody
knows they should be writing them, but nobody does.

Why won’t people write specs? People claim that it’s because they’re
saving time by skipping the spec-writing phase. They act as if
spec-writing was a luxury reserved for NASA space shuttle engineers, or
people who work for giant, established insurance companies. Balderdash.
First of all, failing to write a spec is the single biggest unnecessary risk
you take in a software project. It’s as stupid as setting off to cross
the Mojave desert with just the clothes on your back, hoping to "wing
it." Programmers and software engineers who dive into code without
writing a spec tend to think they’re cool gunslingers, shooting from
the hip. They’re not. They are terribly unproductive. They write bad
code and produce shoddy software, and they threaten their projects by
taking giant risks which are completely uncalled for.

believe that on any non-trivial project (more than about 1 week of
coding or more than 1 programmer), if you don’t have a spec, you will always spend more time and create lower quality code. Here’s why.

The most important function of a spec is to design the program.
Even if you are working on code all by yourself, and you write a spec
solely for your own benefit, the act of writing the spec — describing
how the program works in minute detail — will force you to actually design the program.

Let’s visit two imaginary programmers at two companies. Speedy, at
Hasty Bananas Software, never writes specs. "Specs? We don’t need no
stinkin’ specs!" At the same time, Mr. Rogers, over at The
Well-Tempered Software Company, refuses to write code until the spec is
completely nailed down. These are only two of my many imaginary friends.

Speedy and Mr. Rogers have one thing in common: they are both in
charge of backwards compatibility for version 2.0 of their respective

Speedy decides that the best way to provide backwards compatibility
is to write a converter which simply converts 1.0 version files into
2.0 version files. She starts banging that out. Type, type, type.
Clickety clickety clack. Hard drives spin. Dust flies. After about 2
weeks, she has a reasonable converter. But Speedy’s customers are
unhappy. Speedy’s code will force them to upgrade everyone in the
company at once to the new version. Speedy’s biggest customer, Nanner
Splits Unlimited, refuses to buy the new software. Nanner Splits needs
to know that version 2.0 will still be able to work on version 1.0
files without converting them. Speedy decides to write a backwards converter and then hook it into the "save" function. It’s a bit of a mess, because when you use a version 2.0 feature, it seems to
work, until you go to save the file in 1.0 format. Only then are you
told that the feature you used half an hour ago doesn’t work in the old
file format. So the backwards converter took another two weeks to
write, and it don’t work so nice. Elapsed time, 4 weeks.

Now, Mr. Rogers over at Well-Tempered Software Company (colloquially, "WellTemperSoft") is one of those nerdy organized types who refuses
to write code until he’s got a spec. He spends about 20 minutes
designing the backwards compatibility feature the same way Speedy did,
and comes up with a spec that basically says:

  • When opening a file created with an older version of the product, the file is converted to the new format.

The spec is shown to the customer, who says "wait a minute! We don’t
want to switch everyone at once!" So Mr. Rogers thinks some more, and
amends the spec to say:

  • When opening a file created with an older version of the product,
    the file is converted to the new format in memory. When saving this
    file, the user is given the option to convert it back.

Another 20 minutes have elapsed.

Mr. Rogers’ boss, an object nut, looks at this and thinks something might be amiss. He suggests a different architecture.

  • The code will be factored to use two interfaces: V1 and V2.  V1
    contains all the version one features, and V2, which inherits from V1,
    adds all the new features. Now V1::Save can handle the backwards
    compatibility while V2::Save can be used to save all the new stuff. If
    you’ve opened a V1 file and try to use V2 functionality, the program
    can warn you right away, and you will have to either convert the file
    or give up the new functionality.

20 more minutes.

Mr. Rogers is grumpy. This refactoring will take 3 weeks, instead of the 2 weeks he originally estimated! But it does solve all the customer problems, in an elegant way, so he goes off and does it.

Total elapsed time for Mr. Rogers: 3 weeks and 1 hour. Elapsed time for Speedy: 4 weeks, but Speedy’s code is not as good.

The moral of the story is that with a contrived example, you can
prove anything. Oops. No, that’s not what I meant to say. The moral of
the story is that when you design your product in a human language, it
only takes a few minutes to try thinking about several possibilities,
revising, and improving your design. Nobody feels bad when they delete
a paragraph in a word processor. But when you design your product in a
programming language, it takes weeks to do iterative designs.
What’s worse, a programmer who’s just spend 2 weeks writing some code
is going to be quite attached to that code, no matter how wrong it is.
Nothing Speedy’s boss or customers could say would convince her to
throw away her beautiful converting code, even though that didn’t
represent the best architecture. As a result, the final product tends
to be a compromise between the initial, wrong design and the ideal
design. It was "the best design we could get, given that we’d already
written all this code and we just didn’t want to throw it away." Not
quite as good as "the best design we could get, period."

So that’s giant reason number one to write a spec. Giant reason number two is to save time communicating. When you write a spec, you only have to communicate how the program is supposed to work once.
Everybody on the team can just read the spec. The QA people read it so
that they know how the program is supposed to work and they know what
to test for. The marketing people use it to write their vague vaporware
white papers to throw up on the web site about products that haven’t
been created yet. The business development people misread it to spin
weird fantasies about how the product will cure baldness and warts and
stuff, but it gets investors, so that’s OK. The developers read it so
that they know what code to write. The customers read it to make sure
the developers are building a product that they would want to pay for.
The technical writers read it and write a nice manual (that gets lost
or thrown away, but that’s a different story). The managers read it so that they can look like they know what’s going on in management meetings. And so on.

When you don’t have a spec, all this communication still happens, because it has to, but it happens ad hoc. The QA people fool around with the program willy-nilly, and when something looks odd, they go and interrupt the programmers yet again to ask them another stupid question about how the thing is supposed to work. Besides the fact that this ruins the programmers’ productivity,
the programmers tend to give the answer that corresponds to what they
wrote in the code, rather than the "right answer." So the QA people are
really testing the program against the program rather than the program
against the design, which would be, um, a little bit more useful.

When you don’t have a spec, what happens with the poor technical
writers is the funniest (in a sad kind of way). Tech writers often
don’t have the political clout to interrupt programmers. In many
companies, if tech writers get in the habit of interrupting programmers
to ask how something is supposed to work, the programmers go to their
managers and cry about how they can’t get any work done because of
these [expletive deleted] writers, and could they please keep them away, and the managers, trying to improve productivity, forbid the tech writers to waste any more of their precious
programmers’ time. You can always tell these companies, because the
help files and the manuals don’t give you any more information than you
can figure out from the screen. When you see a message on a screen
which says

  • Would you like to enable LRF-1914 support?

… and you click "Help", a tragicomic help topic comes up which says something like

  • Allows you to choose between LRF-1914 support (default) or no
    LRF-1914 support. If you want LRF-1914 support, choose "Yes" or press
    "Y". If you don’t want  LRF-1914 support, choose "No" or press "N".

Um, thanks. It’s pretty obvious here that the technical writer was trying to cover up the fact that they didn’t know what LRF-1914 support is.
They couldn’t ask the programmer, because (a) they’re embarrassed, or
(b) the programmer is in Hyderabad and they’re in London, or (c) they
have been prohibited by management from interrupting the programmer, or
any other number of corporate pathologies too numerous to mention, but
the fundamental problem is that there wasn’t a spec.

Number three giant important reason to have a spec is that
without a detailed spec, it’s impossible to make a schedule. Not having
a schedule is OK if it’s your PhD and you plan to spend 14 years on the
thing, or if you’re a programmer working on the next Duke Nukem and we’ll ship when we’re good and ready.
But for almost any kind of real business, you just have to know how
long things are going to take, because developing a product costs money. You wouldn’t buy a pair of jeans
without knowing what the price is, so how can a responsible business
decide whether to build a product without knowing how long it will take
and, therefore, how much it will cost? For more on scheduling, read Painless Software Schedules.

A terribly common error is having a debate over how something should be designed, and then never resolving the debate. Brian Valentine, the lead developer on Windows 2000, was famous for his motto "Decisions in 10 minutes or less, or the next one is free."

In too many programming organizations, every time there’s a design debate, nobody ever manages to make a decision,
usually for political reasons. So the programmers only work on
uncontroversial stuff. As time goes on, all the hard decisions are
pushed to the end. These are the most likely projects to fail.
If you are starting a new company around a new technology and you
notice that your company is constitutionally incapable of making
decisions, you might as well close down now and return the money to the
investors, because you ain’t never gonna ship nothing.

Writing a spec is a great way to nail down all those irritating
design decisions, large and small, that get covered up if you don’t
have a spec. Even small decisions can get nailed down with a spec. For
example, if you’re building a web site with membership, you might all
agree that if the user forgets their password, you’ll mail it to them.
Great. But that’s not enough to write the code. To write the code, you
need to know the actual words in that email. At most companies,
programmers aren’t trusted with words that a user might actually see
(and for good reason, much of the time). So a marketing person or a PR
person or some other English major is likely to be required to come up
with the precise wording of the message. "Dear Shlub, Here’s the
password you forgot. Try not to be so careless in the future." When you
force yourself to write a good, complete spec (and I’ll talk a
lot more about that soon), you notice all these things and you either
fix them or at least you mark them with a big red flag.

OK. We’re on the same page now. Specs are motherhood and apple pie.
I suspect that most people understand this, and my rants, while
amusing, aren’t teaching you anything new. So why don’t people write specs? It’s not to save time, because it doesn’t,
and I think most coders recognize this. (In most organizations, the
only "specs" that exist are staccato, one page text documents that a
programmer banged out in Notepad after writing the code and after explaining that damn feature to the three hundredth person.)

think it’s because so many people don’t like to write. Staring at a
blank screen is horribly frustrating. Personally, I overcame my fear of
writing by taking a class in college that required a 3-5 page essay
once a week. Writing is a muscle. The more you write, the more you’ll
be able to write. If you need to write specs and you can’t, start a
journal, create a weblog,
take a creative writing class, or just write a nice letter to every
relative and college roommate you’ve blown off for the last 4 years.
Anything that involves putting words down on paper will improve your
spec writing skills. If you’re a software development manager and the
people who are supposed to be writing specs aren’t, send them off for
one of those two week creative writing classes in the mountains.

If you’ve never worked in a company that does functional
specifications, you may never have seen one. In the next part of this
series, I’ll show you a short, sample spec for you to check out, and
we’ll talk about what a good spec needs to have. Read on!

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