If Version Control Systems were Airlines

March 6th, 2008

Many of you have seen the net classic If Operating Systems Were Airlines. Today, let’s consider what the world might be like if version control systems were airlines…

Before anyone gets mad, this is all in fun, OK?

RCS Airlines: One of the first airlines, from way back when this whole aviation thing was new and exciting. Each RCS flight carries exactly one passenger, which RCS believes is a superior way to fly. Although most RCS airplanes are rusty and battered today, RCS Airlines still retains its historic dedication to security. Each airplane is kept locked as much as possible for safety. Occasionally flights will be delayed for hours because the pilot can’t open the locked plane. When this happens, the pilot will frantically try to get the cell phone number of whoever it is that has locked the plane. When the plane finally gets unlocked, you may be tempted to ask why it was locked for so long. Veteran RCS users have learned that the answer is usually disgusting, and never ask anymore. Main competitor: CP/M airlines.

CVS Airlines: Founded on the belief that they could be more efficient than RCS by carrying multiple passengers per flight. They still carry each passenger in a separate RCS-built airplane, but the airplanes fly in a goose-like “,V” formation. Watch out for layovers, though. It can take hours to merge new passengers into the formation properly, and it might take several attempts to take off afterwards.

CVS flights often feature fights over who gets to fly. CVS piloting fights are legendary; rumor has it that OpenBSD got started after CVS airlines refused to allow a passenger to board on the grounds that he had in the past refused to stow his tray table in the upright and locked position.

CVS airlines mostly counts as customers the “over-50″ crowd who grew up using CVS and don’t like change. Its in-flight magazine features advertisements for balding-reversal treatments and uuencode tools.

Main competitor: AIX airlines.

Subversion Airlines: Started by some grey-haired CVS executives with long, wispy beards, Subversion airlines got started by trying to be “CVS, but better”. Subversion airlines was the first major airline to use planes that seat more than one passenger. Unlike CVS airlines, all passengers on a Subversion flight travel in the same plane.

Subversion airlines is famous for its Soviet-like centralized control. All operations must be approved by the Kremlin, and you are allowed, by the grace of the Party Leader, to gaze at the massive airplanes. Those that have served the Party and Airline well for many years are allowed to enter the Great Shrine of the First-Class Comitter, and actually make changes to the airplanes themselves. Plainclothes Subversion Airlines security agents lurk on every flight, and you should not be surprised to be thrown out an airplane window if you make a joke in bad taste about the pilot’s flying skills.

Subversion airlines thrives on the concept that “photocopying is cheap”. You are encouraged to make photocopies of your ticket, or to photocopy your photo ID, and give copies of each to as many people as you can. At checkin time at the gate, if more than one person arrives with a copy of the same ticket, they are ushered into the “merging room” and each person is given a brick. The door is closed, something magical occurs, and the one person that emerges still able to walk is allowed to board the plane.

Main competitor: Windows airlines with no Administrators allowed.

tla airlines: Founded by one of those eccentric British noblemen, Lord Tom’s airline is the utopian philosopher’s airline. Chafed by the heavy-handed control of Subversion Airlines, tla airlines wants every passenger to be created equal. As you approach the gate area in the terminal, you will find many philosophers occupying the gate area, extolling the virtues of tla airlines. They compare tla airlines to reaching out and touching the heavens, leaving behind the bonds of a ground-based life, actually merging with the stars. Oh, the gorgeous beauty of it all! The things we will see!

As you see people arriving from another flight, you observe that some of them have burn marks. One of them comments that “merging with the stars doesn’t work.” Immediately, a dozen philosophers get in a fight with him, claiming that he simply doesn’t understand what it means to merge with the stars, and that if he gets his inner being in the proper state first, he’ll have a much better experience.

As you board the tla airplane, you obvserve that the jetway is a mile long. The airplane itself reminds you of something of a cross between a gothic cathedral and a level of Doom. There are spectacular archways everywhere, sometimes where they don’t really belong. Each archway is supported by ornate curly braces which you don’t normally see on airplanes, and frankly, you’d rather not, because they look all pointy and confuse the kids.

As you arrive as your destination terminal, you see it too is full of philosophers, most of them dining.

Main competitor: VMS airlines.

Darcs Airlines: Unlike every other airline, this one uses physicists instead of engineers to design its airplanes. One brilliant Darcs physicist has finally come up with The Theory of Everything, and as such, Darcs knows where you want to go before even you do. Darcs airlines prides itself on customer service, and asks your preference for even the tiniest details about your trip.

Each seat pocket features a copy of the Theory of Everything for your reading enjoyment, but nobody actually understands it.

Occasionally, you will find that Darcs pilots get into angry conflicts with the control tower in mid-flight. This results in the control tower revoking your permission to land. Legend has it that one Darcs pilot of a plane with exceptionally large fuel tanks actually resolved his conflict with the tower and landed two weeks after taking off. Experienced Darcs users board with several parachutes: one for themselves, and a few more for the newbies.

The Darcs physicists claim that the Theory of Everything predicted the pilots would act this way, and that all pilots eventually act this way throughout the entire universe. They toil day and night finding a way to adjust the gravitational constant of the universe, thereby reducing the anger factor of the pilots.

Main competitor: OS/2 airlines.

bzr airlines: Founded by a South African who had been injured by a curly brace on tla airlines, bzr airlines aims to be “tla done right”. They have shortened the jetway, gotten rid of the curly braces, chased out the philosophers, and no longer have a vision of merging with the stars. Many that were injured on tla airlines fly bzr airlines, and out of respect for tla airlines, bzr airlines will still honor tla tickets.

bzr passengers consider themselves part of an exclusive club because each flight takes off from a launchpad. They often can be seen standing in the terminal passing out bzr literature, trying to get passengers of other airlines to fly bzr, and can’t understand how other airlines continue to exist while people keep walking past their airplanes.

Main competitor: BeOS Airlines.

Bitkeeper Airlines: One of the world’s faster airlines, Bitkeeper airlines occupied that obscure gate for rich people at the end of the terminal for many years. Tickets on Bitkeeper Airlines were rumored to cost thousands of dollars, and were rare and jealously guarded. Then for awhile, Bitkeeper Airlines started giving away tickets for free, though they also kept around the expensive tickets for those with discriminating tastes. Free tickets were made widely available, but the 3-point type on the back of tickets said that you were never allowed to think about another airline before, after, or during your flight, and some people claimed they actually saw the small print morphing right before their eyes.

Bitkeeper flights often featured arguments over whether people were harboring secret thoughts of other airlines. If you were caught thinking about another airline, you were expected to scream vigorously while being thrown out the escape hatch without a parachute. All of this commotion tarnished the rarified air that the rich people paid to experience, so one day it was decided that there would be a Great Purge, because obviously all free ticket holders had harbored lustful thoughts of other airlines, so they were all thrown off the airplanes simultaneously. Today, people aren’t exactly sure where the Bitkeeper gate is, but everyone suspects it still lurks somewhere.

Main competitor: SCO Airlines.

Mercurial Airlines: The “there’s one right way to do it” airline, Mercurial is a sterile, agile, and shiny airline. Every Mercurial airplane looks identical to every other one, shiny and clean. You could swear that all the passengers look alike too, and as you approach the gate, it seems like you too look like everyone else. Mercurial passengers tend to be a happy bunch, who can’t comprehend anybody that flies Git Airlines. Specks of dirt and dust confuse the pilots, so it is best to make sure you have showered before boarding. It is rumored that, through bolting on more engines, some Mercurial airlines can fly to as many places as Git airlines can, but most Mercurial passengers are content to not worry about that.

Main competitor: Python Airlines.

Git Airlines: The “there’s more than one way to do it” airline, Git flies the world’s largest and fastest airplanes. Git Airlines was founded by some priests who were flying for free on Bitkeeper Airlines and survived the fall after the Great Purge. Git airplanes start as spartan, empty cabins, with no carpeting, chairs, or piloting controls. At the departure gate, each passenger is handed a bag containing 173 standard airplane components, accompanied by a 4×5″ sheet of information on the theory of flight, written in 1950. Once onboard, the passengers use these components to finish out the airplane for flight: installing chairs, rudder controls, etc. Every flight results in a plane assembled in a different way, and passengers on each flight believe they are flying the world’s best airplane. Arguments in the terminal after a flight are common, as passengers from different flights debate the merits of their particular design.

Despite all this, Git planes turn out to be safe, and Git passengers believe they get to their destinations in half the time it takes any other passengers, though sometimes they secretly wonder if the Mercurial flight got there faster. Occasionally, passengers on Git airlines build an airplane that appears to go into a tailspin. When that happens, they simply assemble a tool that lets them go back in time and change history so that it doesn’t crash, although it is rumored that if you are a member of the public watching this happen from the ground, it will lead to seizures.

Git airlines takes special pride in the one piece that passengers don’t have to assemble: the plumbing. Every Git lavatory is equipped with state-of-the-art never-fail plumbing, and the best porcelain washroom fixtures money can buy. None of these cheap plastic toilets like you get on every other airline. Here, we have fine porcelain fixtures.

During a flight, after passengers use the lavatory, they frequently get into arguments with each other about which style of porcelain toilet is the best. These arguments are only resolved by the Zen-like Git Priests, who insist that only inferior passengers need to use a toilet while in the air.

Main competition: Perl Airlines.

Categories: Humor, Programming

Leave a comment

Comments Feed44 Comments

  1. Andre Pang

    I so very rarely ever leave comments on blog posts, but… man, bravo John, this was brilliant :).

    Reply

  2. ccadmin

    Where’s the ClearCase love?

    Reply

    John Goerzen Reply:

    Feel free to write any addendums in the comments ;-) I know ClearCase only by rumor, so I didn’t really feel confident describing an airline trip with it :-)

    Reply

    A. Nony Mouse Reply:

    I’ll start.

    ClearCase flies aircraft that resemble battleships being brought aloft by 25,000 parakeets, all of whom are weighed down by 25,000 pages of documentation, which none of them have ever read.

    Reply

    Trevis Rothwell Reply:

    That’s it!

    Shannon Mann Reply:

    ClearlyThere Airlines (formerly ClearCase for Flight)

    ClearlyThere Airlines holds to the credo ‘flight without the trouble’, as the destination isn’t so much arrived at but built ‘on the fly’. A great deal of expense goes into the process of getting there, which happens out-of-site of the traveller. Their sales spokesperson states, ‘The beauty of ClearlyThere is that the traveller doesn’t really know they are flying. They just appear where they need to be when they want to go.”

    Detractors of ClearlyThere complain that they don’t actually fly, but teleport. ClearlyThere says this is nonsense, there is no such thing as teleportation. Other detractors complain that no-one actually goes anywhere, but, through a combination of drugs and hypnosis, travellers are ‘convinced’ they’ve gone somewhere. The glazed happy look to most of ClearlyThere travellers leads credence to this theory. Others argue the real problem is that you can only go where the airline sends you, and the ‘happy, glazed’ look are the drugs they give you to make you accept the destination as if that was your intended destination.

    ClearlyThere has its issues. ClearlyThere doesn’t actually use pilots, preferring to use expensive ‘Doctors of Transportation and Control’ who handle the act of transportation. Although this approach has merit, as even in-flight collisions can be redirected to ground without apparent damage, the cost can be astronomical. When asked about this problem, ClearlyThere sales staff responded, ‘Of course costs are astronomical. ClearlyThere was designed for spaceflight!’ ClearlyThere spokes people were unavailable for comment when asked when ClearlyThere lite would take travellers.

    Reply

  3. Mark

    Visual Source Safe:
    They’ll get you to your destination (uncomfortably) if your plane doesn’t crash

    Reply

  4. Anonymous

    Perforce Airlines had more than one seat per plane long before Subversion Airlines was dreamed up by those wispy bearded executives. The planes are supersonic but are locked up like those of RCS Airlines, causing delays that make the overall journey time so long that they might as well not use supersonic planes at all.

    Reply

  5. mkc

    RCS airlines: Although they seem antiquated in developed areas, if you’re out in the hinterlands, you can snap your fingers at any time and a plane will immediately appear to whisk you away. With many other airlines, you must wait while they build an entire airport first.

    Reply

  6. mkc

    Visual Source Safe:

    Because of this airline’s record, procedures for scraping their passengers’ remains off the tarmac are widely published.

    Oddly enough, most of the employees of this airline use other airlines instead for their transportation needs.

    Reply

  7. Anonymous

    larch airlines:

    A startup founded by the same person who started TLA Airlines, this was a massively underfunded endeavor with the same lofty goals as TLA Airlines. Due to the lack of investment, planes were mostly created out of reused plastic bottles and duct tape. Flights typically took weeks to arrive, mostly due to well known flaws in the engine design. The engines were held in place with chewing gum, and that gum would routinely get loose and clog the engine. At that point, the plane would have to make an emergency landing and spend hours servicing the engine before being able to take off again.

    The airline was only able to stay in business for a short while before going bankrupt. TLA Airlines was founded after that, and passengers seemed to switch to it.

    Reply

  8. romain

    Awesome post. :)

    Reply

  9. Matt Doar

    Now, that was funny! Great job. The one missing airline is the most common one – making lots of copies of files in random directories.

    A staggering 40% of travellers “fly” this airline, where you arrive at your destination by bouncing from trampoline to trampoline across the country. International flights are occasionally attempted without much success.

    Reply

    John Goerzen Reply:

    Ah yes, how could I have overlooked this one?

    It seems that most of these trampolines get worn and tattered rather quickly, but everyone that uses them still think they look shiny and new.

    Reply

  10. Kartik Mistry

    Perfect. Very nice post, specially git airlines :)

    Reply

  11. Anon

    Ooh. You forgot one point about Mercurial airlines: The terminal for Hg airlines is adjacent to Bzr airlines, but every day, the Hg staff and passengers walk by the Bzr terminal without noticing or even seeing it. If you’re a Bzr passenger, and you ask an Hg airlines representative how to get to the Bzr terminal, they will look at you in a puzzled way and ask if you really mean you’re looking for the Hg terminal.

    Reply

    bialix Reply:

    definitely true.

    Reply

  12. Tiago Pascoal

    If Version control systems were airlines

    Reply

  13. Devolio

    Many of you have seen the net classic If Operating Systems Were Airlines. Today, let’s consider what the world might be like if version control systems were airlines…

    Reply

  14. Daniel Burrows

    Surround Airlines:

    This airline’s flagship airliner is modeled on the successful CVS design. But instead of flying in a V formation, the planes are sealed into the hold of a mammoth flying fortress called the “Emmess Essque Ell” and airlifted, one at a time, to their destination. This decreases the wear and tear on each plane, but tremendously increases the fuel requirements and the time required for each trip. Due to the size and cost of the Emmess Essque Ell, there can only be one per airport, so travellers often find themselves waiting on the tarmac while the Essque Ell ferries planes from an adjacent terminal.

    The planes have a gorgeous new paint job and the usual airline seats have been replaced by large, cushy leather recliners. It is true that customers have complained that the paint rubs off at a touch and that the comfortable recliners tend to tip over backwards, forward, or to just collapse into a small, sad collection of unidentifiable lumpy bits of cloth; however, the airline remains popular nonetheless with the fashion and comfort conscious. The airline’s customer service representatives suggest that customers should wear inexpensive clothing when flying and not lean back “too far”.

    Recent plane models from this airline have apparently attempted to graft spare parts from SVN planes onto the basic CVS frame in order to allow multiple-passenger flights. However, whenever more than one passenger enters a plane at once, they must each press a large red button by the door to register their presence. If this procedure is not followed, the plane will spontaneously fragment in mid-flight. This is not the tragic event one might suppose, as each passenger seat is an independently flightworthy vehicle equipped with an autopilot and enough fuel to safely reach any destination. However, these unfortunate incidents do result in passengers arriving at their destination in a rather chaotic manner, making it difficult to determine which plane the each passenger flew on or which passengers were on any given plane.

    Despite its flaws, this airline is popular with [url=http://en.wikipedia.org/wiki/Entymology]entymoligists[/url], due to the fact that each armrest contains a courtesy PDA in which an enterprising traveler can record all the insects he or she observes while in flight. Any information entered into the PDA is sent to a central database maintained by Surround airlines, and can be cross-referenced and compared to the experiences of other travelers from terminals conveniently located at every Surround gate.

    Reply

  15. snan

    xu la’o gy darcs2 gy danfu lenu nabmi jorne

    Reply

    Aaron Davies Reply:

    Wow, I think that’s the first time I’ve ever seen lojban “in the wild” (xkcd doesn’t count). some time with jbovlaste suggests you asked, “Is darcs2 the solution to the problem of merging?” (I couldn’t figure out what the “gy”s were for. Are they part of the “la’o” quoting construct?) Am I close?

    Reply

  16. Anonymous

    Perforce airlines: planes fly around a single tower connected with long wires. All passenger must communicate any change of physical state with the tower. For example, consuming meal becomes a funny act RSN: requesting permission to open the mouth is a must, another one for swallowing, and every passenger around can have a look on what you are chewing.

    Sometimes the tower operator changes and the new one might forget about previous deals, therefore some passengers get stuck in the middle of the process, for example during their toilet business.

    Reply

  17. Craig

    SCCS Airlines: This airline was around before the invention of flight. Although SCCS had “entities” that resembled what airplanes eventually turned out to be, no passengers were ever witnessed to board or depart from them. These “planes” did seem to fly from place to place however, and the airline remains in business even today.

    Some passengers from other airlines whose flights happened to travel through the Bermuda triangle, have reported strange episodes where they awoke on an SCCS “plane” and found no passengers or pilots on board. As in the great ghost ships on the high seas, the “plane” seemed to steer itself, and passenger noises were heard faintly from far off in the distance, as if much of the activity was all happening in another spacetime. After wandering the SCCS “plane” for a short while, they ended up fogging out and waking up back on their original airliner, with hardly any present time having passed…

    Supporters of the collapsing universe theory believe that each iteration of “The Big Bang” is preserved in a massive SCCS “airplane” which continually circles various points in the world sheet spacetime, and that our current universe is version 7.13.244, build 3a.

    Main competitor: RCS airlines.

    Reply

  18. Anonymous

    I’m thinking Darcs airways actually reminded me of something closer to Haskell airways (i.e., theoretically the best, but suffers from some real life practical issues — e.g, space leaks versus exponential merging).

    Reply

  19. Robert

    The smile on my face will last forever, I suspect…

    Reply

  20. Anonymous

    Dimensions Airlines: There was a movie made about this airline: Snakes on a Plane. It was even worse than it sounds.”

    Reply

  21. Justin Patrin

    Monotone airlines:

    Run by a close group of like-minded Mathematicians who work very hard to ensure that whenever the plane does anything it is doing it correctly. Anything which cannot be proven as correct is usually left to the pilot to handle mid-flight.

    Known for its ability to make multiple copies of a plane in-flight, each with a different pilot. Due to its robust proven correctness and massive tests of each plane as it is finished, these planes tend to merge back to one before landing, although sometimes the multiple planes end up landing at different airports due to disagreements between the pilots. The airline’s workers always say that this is not a bad thing, it is simply how the world works.

    Unfortunately the correctness of the system requires each plane to have a copy of the plans of each plane that came before it, which often leads to flights which are delayed hours, days, or even weeks. Many passengers decide halfway through the pre-flight checks switch airlines and never look back.

    Reply

  22. John Calcote

    Continuus Airlines:

    This airline started as a skunk-works project in Sweden that was sold as a “sort of version control thing” to a few buddies of the designers that happened to run large companies. Eventually enough “buddies” were recruited into the club that the airline became noticeable to IBM, who bought it and renamed it to CMSynergy airlines without changing any functionality.

    This airline will get where you need to go if you don’t care how many stops you have to make along the way, or long it takes to get there. The really neat thing is that it will let you back up to any of the stops along the way if you don’t like where you ended up. Additional flights may merge with your flight along the way between any of the stops. If you happen to back up to a point before one of these mergers takes place, don’t worry, you’ll be fine. It’s the merged passengers that will have to worry.

    If you need to personalize your plane, you may do so, but good luck finding the maintenance manual to do so. If you ask for help from the stewardess, there’s a good chance the plane will crash, so it’s best to just experiment while in flight.

    Reply

  23. Danielle

    We use Accurev here at work, so let me try that.

    Well, I do know that several airlines actually use Accurev and Forrester wrote a case study on one of them about release management (thought it was US Airlines but later learned it was “a US airline” to stay anonymous. It was pretty impressive stuff.

    But to be funny…

    If Accurev were an airline, it would be called Streamlined Airways.

    — Planes would land on time (aka TimeSafety) with cleaner wheels than when they took off.

    — Passengers could book their seats from London, Boston and San Diego and check-in all at the same time without worrying about sitting on one another.

    — Bags would be checked and frequently merged with other good bags in multiple stages to prevent searching every single passenger’s dirty laundry and saving time tracking down bags that didn’t pass the beagle’s sniff test.

    Planes could be diverted from their original destination while in mid-flight and still every passenger would arrive safely, as if by magic. No one would have to be dragged from their seat and dropped without a parachute.

    If Accurev were an airline, it would run on water and burn water vapor to help grow our nation’s farmland…ok, I have to get back to work now… ;-)

    ~D

    Reply

  24. Anonymous

    Let’s elaborate the bzr airlines a bit:

    It is often criticized that bzr airlines is too slow when there are lots of passengers and heavy cargo in the plane. Indeed, some large companies and teams have evaluated bzr airlines not being fast enough for their purposes. However, there is a strong belief among loyal bzr passengers that the speed will improve in the future.

    Experienced passengers sometimes come up with more specialized requirements and ask if bzr airlines can provide the service for them. Quite often the answer is that such specialized services tend to confuse ordinary passengers and hence they shouldn’t be official part of the company. Sometimes passengers establish such services themselves to serve other passengers. The idea is that bzr airlines quite willingly accepts the specialized services provided by individual passengers. Many passengers find these services necessary part of pleasant flying experience. Unfortunately specialized services are sometimes hard to find and they are not available for every flying routes and plane models of bzr airplanes.

    Reply

  25. If Programming Languages Were Christmas Carols | The Changelog

    [...] spring, I posted If Version Contol Systems Were Airlines, which I really enjoyed. Now, because I seem to have a desire to take a good joke way too far, [...]

  26. John skämtar « En annan utsikt från en etta i Ronneby

    [...] hittade jag nu precis två mysiga skämttexter. Den första är från i mars i år och handlar om versionshanteringssystem och blandar dessa med flygbolag. I Uppföljaren skriver John om programmeringsspråk som julsånger. Mycket [...]

  27. sajith

    Oh man, how brilliant is this!

    Reply

  28. If programming languages were… ~ James ‘KodeKrash’ Linden

    [...] Also, don’t miss If version control were airlines. [...]

  29. Jeff

    what about MKS?

    Reply

  30. Tanmaya

    Danielle, that was great! We too use Accurev after a lengthy ordeal with VSS, CVS and SVN. I wish I had your creativity! Accurev is the best!

    I have used MKS, Dimensions and Clearcase, too. Those tools are great fodder for some hilarious airline horror stories. More more!

    Reply

  31. Sean

    This may not be a unique feature of Subversion, but a side-effect of Photocopies are Cheap is that in many cases entire Subversion flights will be found copied in partial, complete, or in worst case, iteratively nested state at the airport long after they are supposed to have departed. This copied flights can pose a problem for small airports, as they are usually invisible and only discovered when Air Traffic Control or the general airport management suddenly cannot find room to take on any more passengers or land any pending flights. Getting rid of such copied flights tends to involve either tracking down every copy of every ticket produced in relation to the flight, acting in direct opposition to the Party, or else destroying half the airport.

    Reply

  32. Sarwar Faruque

    Awesome read, love the part about “Zen-like Git Priests”!

    Reply

  33. Rich

    Accurev airlines lets you fly from one city to another (say Boston to San Francisco), but you can’t fly back again. Instead you have to “revert” your original flight, an operation involving creating a new version of Boston and flying to that.

    When you arrive at the airport, don’t tell Accurev airlines that you want to “check in” for your flight. They won’t know what you’re talking about. Tell them you wish to “promote” yourself to San Francisco.

    Safety is an important part of Accurev airlines. Planes might occasionally crash, but if they do, you can always back up to an older version where you are still alive. They call this “time safety”.

    It’s a great airline! :-)

    Reply

  34. Girish Ramakrishnan

    Hilarious, I thought the Git Airlines was the best.

    Reply

  35. dilipm

    amazingly Hilarious! Lol!

    Reply

  36. Destillat #10 | duetsch.info - Open Source, Wet-, Web-, Software

    [...] Versionierung: If Version Control Systems were Airlines [...]

  37. zanshin.net » Version Control Systems as Airlines » Blog Archive

    [...] If Version Control Systems Were Airlines → So far I’ve flown “commercially” on RCS, CVS, and Subversion. Privately I’ve flown on Subversion and Mercurial. Lately I’ve been attempting a flight or three on a home-built Git plane. [...]

Leave a comment

 

Feed

http://changelog.complete.org / If Version Control Systems were Airlines