API
An API is the set of calls one program offers another: an address to send to, a shape to send in, and an answer that comes back as data.
In more detail
A website is built for a person: pages to read, buttons to press, and a shape on the screen that means something to eyes. A program has neither eyes nor patience, so it is offered the same service stripped of all that — an address, a way of stating what is wanted, and an answer with nothing decorative in it.
What makes it useful is that it never varies. The same call, sent a thousand times, is read the same way a thousand times, which is what lets a program lean on it without anybody watching.
What it does on a real document
Here the whole API is one call. Your program writes down the document it wants, sends it, and the finished PDF comes back in the answer to that same call — no queue to watch, no file to fetch afterwards.
Everything a document can hold is said in that one description: the text, the tables, the pictures, the codes, the form to fill in, the standard the file claims. That is why the reference for it is a list of keys rather than a list of calls.
Where it comes from, and why
Programs have called one another since long before the web; what the web changed is that the call now travels over the same wires and in the same language as an ordinary page. A service anybody can reach became a service any program can reach.
The habit of sending a description and getting a finished thing back — rather than driving a machine step by step — is what makes such a service replaceable: two providers that read the same description are two providers you can choose between.
See it on a finished document
The rules behind this word, and the texts they are read from
Glossary
- standard
- A rule argued out in committee, published under a number anybody may buy and read, and identical for every firm claiming it. A claim to follow one can therefore be checked against the text. A way of working that merely spread because it worked is a habit of the trade: useful, widespread, and answerable to no text at all.