RESTful APIs are everywhere. This is funny, because how many people really know what “RESTful” is supposed to mean?

I think most of us can empathize with this Hacker News poster:

I’ve read several articles about REST, even a bit of the original paper. But I still have quite a vague idea about what it is. I’m beginning to think that nobody knows, that it’s simply a very poorly defined concept.

I had planned to write a blog post exploring how REST came to be such a dominant paradigm for communication across the internet. I started my research by reading Roy Fielding’s 2000 dissertation, which introduced REST to the world. After reading Fielding’s dissertation, I realized that the much more interesting story here is how Fielding’s ideas came to be so widely misunderstood.

A differential analyzer is a mechanical, analog computer that can solve differential equations. Differential analyzers aren’t used anymore because even a cheap laptop can solve the same equations much faster—and can do it in the background while you stream the new season of Westworld on HBO. Before the invention of digital computers though, differential analyzers allowed mathematicians to make calculations that would not have been practical otherwise.

In 1993, id Software released the first-person shooter Doom, which quickly became a phenomenon. The game is now considered one of the most influential games of all time.

A decade after Doom’s release, in 2003, journalist David Kushner published a book about id Software called Masters of Doom, which has since become the canonical account of Doom’s creation. I read Masters of Doom a few years ago and don’t remember much of it now, but there was one story in the book about lead programmer John Carmack that has stuck with me. This is a loose gloss of the story (see below for the full details), but essentially, early in the development of Doom, Carmack realized that the 3D renderer he had written for the game slowed to a crawl when trying to render certain levels. This was unacceptable, because Doom was supposed to be action-packed and frenetic. So Carmack, realizing the problem with his renderer was fundamental enough that he would need to find a better rendering algorithm, started reading research papers. He eventually implemented a technique called “binary space partitioning,” never before used in a video game, that dramatically sped up the Doom engine.

The story of Microsoft’s founding is one of the most famous episodes in computing history. In 1975, Paul Allen flew out to Albuquerque to demonstrate the BASIC interpreter that he and Bill Gates had written for the Altair microcomputer. Because neither of them had a working Altair, Allen and Gates tested their interpreter using an emulator that they wrote and ran on Harvard’s computer system. The emulator was based on nothing more than the published specifications for the Intel 8080 processor. When Allen finally ran their interpreter on a real Altair—in front of the person he and Gates hoped would buy their software—he had no idea if it would work. But it did. The next month, Allen and Gates officially founded their new company.

Over a century before Allen and Gates wrote their BASIC interpreter, Ada Lovelace wrote and published a computer program. She, too, wrote a program for a computer that had only been described to her. But her program, unlike the Microsoft BASIC interpreter, was never run, because the computer she was targeting was never built.

It’s hard to believe today, but the relational database was once the cool new kid on the block. In 2017, the relational model competes with all sorts of cutting-edge NoSQL technologies that make relational database systems seem old-fashioned and boring. Yet, 50 years ago, none of the dominant database systems were relational. Nobody had thought to structure their data that way. When the relational model did come along, it was a radical new idea that revolutionized the database world and spawned a multi-billion dollar industry.