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[Seminar] [A Programmer's Introduction to APIs]

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[Billy Janitsch] [Harvard University] [Tommy MacWilliam]

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[This is CS50.] [CS50.TV]

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>> Hi, everyone, I'm Billy, and today I'm going to be talking about APIs,

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or application programming interfaces,

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specifically in the context of CS50 final projects and that sort of thing.

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In general what is an API?

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In very broad terms, it's sort of a middle man that allows 2 pieces 

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of software to communicate with each other.

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That's a kind of very broad definition and isn't that relevant for what we're looking at.

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What we really want is some sort of useful middle ground

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to communicate with some sort of database somewhere.

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>> Here's a chart, and basically the idea is that

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we are an application, and we want to get data from a database,

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but we don't want to query the database directly.

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Instead we want to go through this sort of middle man, the API.

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The idea behind that is numbers 2 and 3 on the chart

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are both going to be very complicated and messy.

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In other words, when the API is querying the database,

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it's probably going to be using SQL tables and all of that sort of stuff,

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and we've learned a bit about it in CS50, but overall,

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you've noticed that it's a bit of a pain.

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It gets very, very complicated and messy, especially when you're making

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complex queries and that sort of thing.

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>> What we really want is some sort of useful and simple way

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to get that data, and that's the idea behind numbers 1 and 4 on the chart.

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In other words, we want a really simple way to tell the API what to get for us

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and a really simple way to get that data back.

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There is one main way that that data is usually sent and received,

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which is JSON, or JavaScript Object Notation.

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That can vary a little bit as far as how you send the request to the API.

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In other words, if you want some certain amount of data,

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how you tell the API to get that data can vary a little bit.

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Usually it involves making some sort of network request.

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In other words, accessing some sort of URL that's going to tell the API

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exactly what you want, but the data is almost always sent back,

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in other words, number 4 in JSON.

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>> What is JSON exactly?

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As I said, JavaScript Object Notation.

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It's basically the universal standard for transmitting and receiving data.

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The idea is that you have these 3 categories of things.

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You have arrays, hashmaps, and primitives.

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Arrays and hashmaps you've looked at a little bit in CS50,

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but you've sort of gotten a very strict sense of what they are.

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In other words, with arrays you know that they're type bound,

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so you only have one sort of type that goes throughout the entire array.

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JSON is a lot more lenient with that sort of thing.

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Basically the idea is you construct this object,

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which can be composed of any of these 3 things

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and can be composed of multiple ones of them, and they can be nested.

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>> Here's sort of an example of JSON,

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which is these curly brackets here represent your hashmap,

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and a hashmap is basically a mapping from some sort of key

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to some sort of value.

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You'll see here that we have the properties key,

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and that's mapping onto an array, which is this whole thing.

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We see another element of the hashmap, which is this key isAwesome,

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which maps to a primitive value of true, in other words, a boolean.

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Primitives can be strings. They can be integers.

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They can be bools, anything like that.

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And you see the contents of this array that properties points to has 2 strings in it,

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self-similar and wonderful.

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Those are 2 properties of JSON, and we see that JSON is awesome.

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To look at that a little more closely I'm going to construct

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a more complex example of JSON here.

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>> Let's start with an array, for example, just an empty array.

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But that's sort of boring, so we're going to fill it up a bit,

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and as I said, arrays in JSON are type bound,

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so we could also have a string here, which is hi, 

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and that's another element of that array.

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And likewise, we could add a hashmapping here, which is going to have a few mappings.

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It's going to have a mapping from name to the string Billy.

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We have a mapping from name to Billy, and we have a mapping of 

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favorite color to blue.

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That's basically a good example of JSON.

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It kind of gets into—whoops, need a comma there—all of the different parts of it.

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Again, it's not type bound at all, so you can have any kind of types

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inside anything you want, and the idea is it's self-similar.

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In other words, this right here is a JSON object, as is this whole thing,

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as is just this, so you can have a primitive be an object, 

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an array be an object or a hashmap be an object.

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>> As you can kind of see, JSON is really, really useful in that it's so versatile.

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You can have any possible data that you can conceive stored in JSON.

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That makes it a really nice language to use with APIs

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because it pretty much means that no matter what data that you want

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there's going to be some way to get it back in JSON.

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A few properties that make JSON particularly good for this sort of thing.

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As you can see, compared to a lot of things that you've been working with in CS50

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it's comparatively very easy to read and also very easy to write.

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You can indent it out if you want, like I was doing in that example,

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which gives you a nice, pretty version that you can see really well.

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But moreover, it's also easy to read and write for a computer. 

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In other words, it's easy to parse and easy to encode,

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which means that it's pretty fast as far as reading the data is concerned,

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and JSON can be generated really quickly.

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>> It's also very easy to access different parts of JSON and that sort of thing.

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That's nice, and furthermore, the fact that it's self-similar,

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in other words, the fact that you can have JSON within JSON within JSON

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is really nice for storing data.

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Another part that is generally really useful in working with APIs is jQuery.

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You've learned a little bit of JavaScript, which is a nice way

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to manipulate HTML and CSS within a website.

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But it can kind of be a pain to code in plain JavaScript,

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largely because JavaScript is a really verbose language.

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You have to learn a lot of syntax, and just to do very simple things

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it takes a lot of code, so jQuery is a library for JavaScript.

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In other words, it's a JavaScript file that you can load 

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and then use jQuery functions to do certain things.

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And jQuery basically makes your life a whole lot easier.

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It simplifies what would take hundreds of lines in JavaScript down to a few lines in jQuery.

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>> It's particularly useful if you're using APIs because generally

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how you'll be accessing APIs is by making AJAX requests,

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and I believe David has mentioned in lecture that AJAX requests

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are generally when you're making a network request to some sort of server

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and getting back some sort of data and updating a page instantaneously.

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Whereas in plain JavaScript that would take crazy numbers of lines

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to validate all of the headers and do all of that sort of stuff,

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jQuery has a really simple function called AJAX,

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and all you have to do in AJAX is give the parameters that you want to give the API,

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the location of the API and any additional sort of options that you want to configure.

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It's really, really nice and very useful for this kind of thing.

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That's all we need to start getting our hands dirty in APIs.

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>> I'm going to bring up a few examples and explore their different properties

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and why they're useful for different kinds of things.

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The first thing I'll actually show you is something that I'm working on 

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at my research lab, which is an Ngram Viewer,

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and basically the idea of an Ngram Viewer is you can search for some kind of word

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or phrase and see how often it's appeared in a certain set of text over time.

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This example here is this data set of babies

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that were born in New York between 1920 and 2000.

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We can search, for example, for the name Jennifer,

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and we see that pre-1960s it really wasn't used all that much,

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and then as we get into later years it's becoming used more and more.

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We can also do comparisons, so if we compare Jennifer to, for example, Thomas,

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we can see Thomas has been pretty prevalent throughout history,

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whereas Jennifer is a more recent name.

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We can do that kind of thing.

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>> How does this application work?

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Basically, it works via an API.

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In other words, we have certain parameters here.

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We have the parameters of what we're actually searching for,

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which are these names, and then we have a few other properties,

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like the Y axis and the X axis.

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You can see we have a few different options as far as the 

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time resolution to use and that sort of thing.

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We have these options as far as what data we actually want from the database,

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and we want to get that data back in some useful way.

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Ordinarily, if we were querying the database directly it would sort of be a pain to do

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because presumably this data about baby names lives in some database somewhere,

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and it would be really complicated to have to query it manually

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and decide exactly what data to return.

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In other words, we only care about Jennifer and Thomas in this case,

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and we only care about on a certain axis and all of that sort of stuff.

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>> How do we get around this?

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To dig into this API a little more I'll show you another example of this platform

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which uses a slightly different data set.

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This data set, instead of being baby names, is actually just the entire

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print publication database of Open Library,

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which is a giant source of texts published throughout the last 100 or so years.

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The idea is we have this compository of millions and millions of text,

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which we can now search for different words and phrases in.

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Here's an example that varies a little differently from the previous example 

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I showed you, which is we have these 3 search queries,

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war, war, and the French word for war, which is guerre.

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And we're searching within 3 different sections of the total database.

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In other words, in this first query we're only searching in the USA,

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in the second one only in the UK, and the third only from works published in France.

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We see some interesting patterns emerge.

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For example, we see right around here which—

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oops, I messed up the axis a little bit, but you can see right in this range here

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around the Civil War there's a big spike in the American edition

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but not such a big spike in the other two, and that's obviously because 

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the American Civil War was happening at that point.

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>> We can see some cool stuff there,

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but what we really care about is how we got this data.

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I'll take you behind the scenes in this app in a little bit.

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A neat trick is if you're working with the site and kind of want to know

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what's going on behind the scenes, you can open up the developer tools.

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I'm going to be using Chrome's developer tools, and to get to those

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you can do control, shift, J, and that takes you to the JavaScript console.

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There are a few tabs here. 

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They can all be pretty useful under different circumstances, but I care about the network

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tab right now, and I actually have to refresh to get that working.

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Oh, sorry.

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It likes to give a random example.

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Okay, we'll use this example instead then.

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>> The idea is there's this API here,

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and you can see exactly what the API is returning.

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This is what the application is getting back from the API having sent that request.

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Let me zoom in a little bit, 

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and we can basically see it's just a series of key value pairs in JSON.

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In other words, we have this hashmap here that's mapping values.

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In other words, it's mapping years to values.

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In 1765 whatever word we initially searched for is used 90 times 

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out of 1 million, so we're getting back this result.

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It's not exactly JSON since we have this little result header here,

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but notice that this whole object here is just a great big JSON blob.

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We have an array here which contains this whole element,

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and you can see that whole element ends there, and then we have another big element

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that goes all the way down to the end, and that ends here.

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We have a really big array with 2 objects in it, 

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and each of those objects is a hashmap.

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You can see within each of those hashmaps we have a mapping 

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of this index value to 0 and this value's value to another hashmap,

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which again is mapping X axis values to Y axis values.

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>> You can see JSON gets a little bit complicated, but overall, 

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it's actually very useful, and it's very easy to access compared to

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other different forms of notation.

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As far as what we're actually sending data to the API to get,

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I'm going to go into the back end a little bit here.

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This is the big JavaScript file that's handling all of the interactions of the web app,

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and so we don't care about most of this, but we do care about some of it.

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For example, we care about this buildQuery function,

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and the idea of this function is basically it's looking around the page,

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figuring out what the user wants to query, in other words,

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checking those boxes where they've input their search terms,

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checking the different Y and X axis values that they've chosen and all of that sort of thing,

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and it's going to spit out this query value, which I can then send off to the API.

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>> This looks complicated, and it is pretty complicated

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but what I'm going to do—in fact, I'm already doing this, which is great—

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is that I'm going to get the console to print out exactly that query value 

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that it's sending off to the API.

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That's actually right here. Sorry, it outputs a lot of things.

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But this is what we care about, this object right here.

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This is the query object.

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In other words, this is exactly what the web application is sending to the API,

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and so let's look inside a little bit, and we see we have a few values here.

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We see we have this count type, which is occurrences per million words,

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which is exactly what we've chosen in the Y axis over here.

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That's where that's coming from.

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We have a database value, which means that there's some certain database

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that this data is living in, and we want to access that data specifically

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as opposed to the baby names data, for example.

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Then we have this groups value,

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which is saying that we want to search by year as opposed to 

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any other X axis value.

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Then we have a method, which some APIs will do multiple things.

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In other words, this API can also return other kinds of data, 

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but in this case, we want that mapping of X axis values to Y axis values.

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That's what that is telling it to do there,

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and we have this search limits array, which contains 2 values.

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The first one is what we see here, which is all of the values

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contained within that first little box at the top.

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>> In other words, we want to look for the word battle, and we want to filter it

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by English texts within American literature.

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We have this country, which is USA.

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We have a language, which is English, so we have all of these different parts

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that are all telling the API exactly what we want.

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We don't know what the data that we get back is yet,

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but we know that the data is going to take a certain form.

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This example is sort of on the complicated side,

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and you wouldn't necessarily be using an API this complex,

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but this is to show you the range and power of what APIs can do.

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In other words, using a relatively simple query system we basically have an input box

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with a few other selectors in different places.

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>> Let me zoom back out here.

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We have an input box with a few different metadata selections,

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and we have Y axis and X axis selections.

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We don't actually have that many fields,

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and we can see very easily we're able to query some sort of API

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and get data back and then put it into this chart, 

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which is then going to display it in a useful way.

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To look at another example that might be a bit more familiar to you guys

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we're going to turn to Facebook.

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Facebook's API is called the Facebook Graph,

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and basically what that means is Facebook sees itself as this massive database

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of lots of different parts that all have certain relationships to each other.

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In other words, I'm a user on Facebook, so I have a profile,

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and I also have certain friends, and each of them has a profile,

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and each of my friends has a wall, which has different comments on it,

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and each of those comments has likes and all of that sort of thing.

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>> There's lots of different parts to Facebook.

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It's a hugely complex API, and there's tons you can do with it,

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but it's actually pretty simple to use.

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I'm going to start out by going to graph.facebook.com/billyjanitsch,

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which is my unique account name, and your account name will either be

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some kind of word if you've chosen it, or it might just be a string of numbers.

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What we get back is pretty basic information.

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We see that I have a first name, which is Billy, a last name, which is Janitsch.

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There's a unique Facebook ID which I have.

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You can see that I'm male and that I have my language setting 

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to British English.

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In other words, we're seeing very basic information here.

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It's not too much, but it does give us an idea of what's there.

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>> We can do the same thing to David Malan, for example.

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I think his name is dmalan.

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We see David Malan has a unique ID.

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He has a name, first name, middle name, last name.

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We also see that he's male and has his language set to US English.

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In other words, we're seeing pretty basic information here.

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Now, what happens if we try to check out something else?

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Let's say I'm interested in what David Malan has liked on Facebook.

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I can do /likes. Now we've run into a problem.

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We've got some sort of error that says an access token 

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is required to request this resource.

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But if you think about it, that actually makes sense because it would be weird

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if you could access every single part of Facebook's database

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just from some sort of simple API, right?

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In other words, presumably your information can't be accessed by anyone who wants it.

300
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>> This error is precisely what that means.

301
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Some APIs require certain permissions in order to access their data.

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And even more advanced APIs, like the Facebook one,

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will require certain permissions to do certain things.

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I can see this basic information about David Malan.

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I can see that he's male and that he lives in the US,

306
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but I can't really see anything past that.

307
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To get around this for now, Facebook has this nice tool 

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which is the graph API explorer, and the idea of that is you can sort of 

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make up permissions for yourself based on your own account

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and then view things that specifically your account can view.

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For example, if I do graph.facebook.com/billyjanitsch/likes—

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whoops, I guess I have to revalidate my token here.

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Okay.

314
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If I do that again, great, now I see that I get this object back

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which says that I like pool noodles, which are in the category Games and Toys.

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I like walruses, which are in the category Animal.

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These are my actual Facebook likes. 

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They're kind of embarrassing.

319
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>> But we can see this data is all returned in JSON.

320
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It's pretty readable.

321
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In other words, we have this mapping of data to some sort of an array,

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and each element of this array is a hashmap which maps

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the name of a like and the category of a like.

324
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Each like has a unique ID.

325
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There are all sorts of different things of data that we can get,

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and if you're interested in using the Facebook API for a CS50 final project

327
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or for anything like that it's actually quite doable.

328
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Basically how you get around the authentication thing is Facebook 

329
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uses a system called OAuth, or Open Authentication,

330
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and I don't want to get into it now because OAuth or the different type

331
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of authentication tends to vary a lot between different APIs,

332
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so I could spend a long time going over each one, 

333
00:19:58,320 --> 00:20:01,170
but they're actually pretty self-explanatory.

334
00:20:01,170 --> 00:20:04,050
>> If you Google Facebook API it's very readable.

335
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There's a whole spec.

336
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For example, this is the documentation for the Facebook API,

337
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and you can see I'm on the User page, so I can learn all about the different kinds of things

338
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that are available to get as far as data

339
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and also the different permissions that I need in order to access them.

340
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As we saw, we don't need permissions to access the name or the gender,

341
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but beyond that we do need permissions for most things.

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This page, or rather, this website will also tell you how to get 

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a token to be able to authenticate yourself.

344
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Most authentication systems use some sort of token

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where you get this unique value, which is a really long and random string,

346
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and that way they can associate the request that you're making with you.

347
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In other words, they know that you're not doing anything suspicious with their data.

348
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They know exactly what you're getting.

349
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They also know that you have permission to view that information.

350
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>> If you've made a Facebook app and your app has certain users,

351
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and those users have allowed that app to access certain parts of their profile,

352
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then whatever API key or token that that app is using

353
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will be able to access the data for those users.

354
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This might sound complicated, but it's not too bad,

355
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and if you want to use Facebook I would highly recommend that you 

356
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consider playing around with their API.

357
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It's very cool, and you can do a lot of different things with it.

358
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If the user grants you these permissions you can even go back to the API

359
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and say I want to actually post to this user's wall, or I want to have them post a photo,

360
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and that's why on your news feed you'll sometimes get those annoying things

361
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saying your friend has watched this video on some sort of weird site or something like that.

362
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That's because that app has been granted access to post on that person's wall.

363
00:21:43,120 --> 00:21:48,350
The idea overall, the Facebook API is pretty complicated but also really useful.

364
00:21:48,350 --> 00:21:53,220
Definitely worth checking out if you're still looking for a final project.

365
00:21:53,220 --> 00:21:57,930
>> Another suite of APIs that I'm going to go over is CS50 APIs.

366
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Let me zoom in here.

367
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CS50 has actually put together a whole series of APIs

368
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that you can use for a final project or just for anything that you're making.

369
00:22:07,080 --> 00:22:12,830
And they're mostly Harvard related, and they vary from the HUDS menu,

370
00:22:12,830 --> 00:22:17,780
for example, to this Harvard Events API, which will let you access a list of

371
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different events that are going on at Harvard and that sort of thing.

372
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And so we can click on any one of these and get a spec for it,

373
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which you'll be able to find for any API, and the idea is 

374
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it lets you know, A, specifically what to request from the API and how to request it.

375
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In other words, if I want all events that are happening tomorrow

376
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then I've got to obviously give it that date that I want in a certain format,

377
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and B, it will tell me exactly what it's going to give back to me.

378
00:22:46,030 --> 00:22:48,590
It will say I'm going to return you this JSON object, 

379
00:22:48,590 --> 00:22:50,960
or like you can see, there are different formats.

380
00:22:50,960 --> 00:22:54,050
>> You can also return the data as a CSV, for example.

381
00:22:54,050 --> 00:22:57,620
But you know exactly how that data is going to look when you get it back

382
00:22:57,620 --> 00:23:00,610
so you can expect to do certain things with it.

383
00:23:00,610 --> 00:23:07,240
We can scroll down and see, for example, if we want to query the API

384
00:23:07,240 --> 00:23:11,500
to get a calendar, then we can use this particular URL

385
00:23:11,500 --> 00:23:16,480
and give it certain parameters which are going to be the data that we want exactly.

386
00:23:16,480 --> 00:23:19,540
And likewise, if we want the data back in a certain format,

387
00:23:19,540 --> 00:23:23,790
then we can ask it to output the data in a CSV,

388
00:23:23,790 --> 00:23:27,700
and that's just another parameter that we're passing to the API.

389
00:23:27,700 --> 00:23:29,210
Lots of cool things to do there. 

390
00:23:29,210 --> 00:23:32,550
I would definitely recommend checking out the CS50 APIs.

391
00:23:32,550 --> 00:23:36,000
>> I'm going to look at this Harvard Food API in particular for a little bit.

392
00:23:36,000 --> 00:23:39,870
One thing I've actually designed is this Harvard Noms website,

393
00:23:39,870 --> 00:23:44,930
which uses the CS50 Food API to retrieve the HUDS menu for the day.

394
00:23:44,930 --> 00:23:50,400
And for extension school people, HUDS is the dining service at Harvard.

395
00:23:50,400 --> 00:23:55,130
What you get is this page which contains all of the meals for the day, so we see lunch.

396
00:23:55,130 --> 00:23:58,130
We have a few different categories. We have the bean and whole grain station.

397
00:23:58,130 --> 00:24:00,340
We have the brown rice station.

398
00:24:00,340 --> 00:24:03,360
We can see for brunch we have these few food items.

399
00:24:03,360 --> 00:24:07,030
If we click on them, then we get the nutrition information.

400
00:24:07,030 --> 00:24:12,240
You see this is the nutrition information for grapefruit, in case you were wondering.

401
00:24:12,240 --> 00:24:14,870
And so again, we're going to peer into the back end here a little bit 

402
00:24:14,870 --> 00:24:18,530
and see what exactly this is doing to get this data.

403
00:24:18,530 --> 00:24:21,710
And it turns out to not actually be very complex at all.

404
00:24:21,710 --> 00:24:28,720
This file looks a little messy, but keep in mind that this is handling the entire website,

405
00:24:28,720 --> 00:24:34,130
and if I scroll down we see this change data function.

406
00:24:34,130 --> 00:24:36,630
>> Now, just to be clear, this is written in CoffeeScript,

407
00:24:36,630 --> 00:24:39,570
which is a language that you probably haven't seen before.

408
00:24:39,570 --> 00:24:44,810
But it's pretty readable, so I'll walk through it as though it were pseudocode.

409
00:24:44,810 --> 00:24:49,080
Change date is a function that's going to take in this date value,

410
00:24:49,080 --> 00:24:51,740
and it's also going to take in a first, which we don't care about as much.

411
00:24:51,740 --> 00:24:54,110
But the important thing is that it has this date,

412
00:24:54,110 --> 00:25:00,080
and that date is the day that we want to request all of the food items for.

413
00:25:00,080 --> 00:25:04,030
And then you see we have a little bit of syntax here,

414
00:25:04,030 --> 00:25:09,000
which is basically parsing that date into a readable format.

415
00:25:09,000 --> 00:25:11,920
In other words, the API requires the date in a certain format.

416
00:25:11,920 --> 00:25:17,390
You can't just say November 16th, 2012 AD.

417
00:25:17,390 --> 00:25:20,320
It won't know what to do with that. It wants the date in a specific format.

418
00:25:20,320 --> 00:25:23,230
All we're doing here is giving it exactly that format, 

419
00:25:23,230 --> 00:25:26,520
which is a year value and then a hyphen, a month value, 

420
00:25:26,520 --> 00:25:29,420
another hyphen and the date value.

421
00:25:29,420 --> 00:25:34,910
And we also say we want the data to be output in JSON.

422
00:25:34,910 --> 00:25:37,560
>> Now we're making this AJAX request, and as I mentioned earlier,

423
00:25:37,560 --> 00:25:41,680
jQuery has this super useful AJAX function which all you need to do is specify

424
00:25:41,680 --> 00:25:45,780
a few parameters down here, and it will give you back exactly what you want.

425
00:25:45,780 --> 00:25:50,490
We're telling it that the URL we want it to go to is this CS50 Food API,

426
00:25:50,490 --> 00:25:52,270
which we got from the spec.

427
00:25:52,270 --> 00:25:56,730
We say that we want the data in JSON and that 

428
00:25:56,730 --> 00:25:59,490
we're going to give it this data which we've defined up here.

429
00:25:59,490 --> 00:26:02,670
This is the day we want the food items for.

430
00:26:02,670 --> 00:26:07,790
And then all we have to do is define some sort of success function,

431
00:26:07,790 --> 00:26:11,980
which is basically what happens when the API returns that data.

432
00:26:11,980 --> 00:26:15,490
In other words, we've packaged up all of the parameters that we want,

433
00:26:15,490 --> 00:26:20,530
which in this case is the day that we want it and the fact that we want it in JSON,

434
00:26:20,530 --> 00:26:23,840
and we sent it off to the API, so now the API is saying, okay,

435
00:26:23,840 --> 00:26:26,350
here is your data, I got it back for you.

436
00:26:26,350 --> 00:26:29,930
We have the success function, which means given that the API

437
00:26:29,930 --> 00:26:32,230
successfully returns some data, what do we do with it?

438
00:26:32,230 --> 00:26:35,980
>> And it turns out that all we do is call this update menu function

439
00:26:35,980 --> 00:26:42,680
with whatever the API has returned, so we can search for that

440
00:26:42,680 --> 00:26:47,970
and see that all we're doing is using a bunch of new syntax here

441
00:26:47,970 --> 00:26:52,220
to update the HTML and insert this new data.

442
00:26:52,220 --> 00:26:56,580
What this allows is we have these arrows on either side, and we can click,

443
00:26:56,580 --> 00:27:01,060
and now we're looking at the data for the next day and again for the next day,

444
00:27:01,060 --> 00:27:04,820
and each time it's updating that date value and querying the API,

445
00:27:04,820 --> 00:27:07,510
getting back some data and putting it into the site.

446
00:27:07,510 --> 00:27:10,590
Again, you can see, super, super useful.

447
00:27:10,590 --> 00:27:14,410
This app took me a few hours to hack together,

448
00:27:14,410 --> 00:27:20,140
and I have a bit more experience, obviously, but your CS50 final project

449
00:27:20,140 --> 00:27:22,870
can look something very much like this.

450
00:27:22,870 --> 00:27:29,540
>> APIs are super powerful for the amount of effort that they take.

451
00:27:29,540 --> 00:27:32,800
The last thing I'm going to go over is a few more APIs broadly.

452
00:27:32,800 --> 00:27:35,480
I won't get as far into them as far as what they do specifically,

453
00:27:35,480 --> 00:27:38,740
but I'll give you an idea of what's out there.

454
00:27:38,740 --> 00:27:42,700
2 really useful ones, if you're interested in data analysis or visualization 

455
00:27:42,700 --> 00:27:45,960
or anything like that, are Freebase and Wikipedia.

456
00:27:45,960 --> 00:27:49,800
Wikipedia—presumably you all know—is a free online encyclopedia,

457
00:27:49,800 --> 00:27:53,230
and it actually has an API, so if you want to, for example,

458
00:27:53,230 --> 00:27:56,250
get all of the texts and the articles for octopus

459
00:27:56,250 --> 00:27:58,030
you can very easily do that.

460
00:27:58,030 --> 00:28:02,300
Just say hey, Wikipedia API, I'd like the data returned as this,

461
00:28:02,300 --> 00:28:07,010
and I'd like it in this format, and the article I'd like is octopus,

462
00:28:07,010 --> 00:28:09,820
and very quickly it will give you back that information.

463
00:28:09,820 --> 00:28:12,230
That can be really useful if you want to make some sort of site

464
00:28:12,230 --> 00:28:16,200
that's a better viewer for Wikipedia or something like that.

465
00:28:16,200 --> 00:28:21,350
>> Freebase is sort of similar, although it's a little bit harder as far as API.

466
00:28:21,350 --> 00:28:24,390
Freebase is like Wikipedia in that it's an online encyclopedia

467
00:28:24,390 --> 00:28:29,050
which contains lots and lots of different data about all sorts of different topics,

468
00:28:29,050 --> 00:28:33,150
but it's stored in a relational database, which is slightly different from Wikipedia.

469
00:28:33,150 --> 00:28:36,410
Wikipedia has its articles and articles linked to other articles,

470
00:28:36,410 --> 00:28:38,860
but for the most part, if you want the data for octopus,

471
00:28:38,860 --> 00:28:41,990
you go to the octopus article, get that data, and you have a bunch of text

472
00:28:41,990 --> 00:28:43,830
about octopuses, so that's great.

473
00:28:43,830 --> 00:28:46,870
Freebase works in a slightly more complicated manner in that

474
00:28:46,870 --> 00:28:48,930
everything is related to one another.

475
00:28:48,930 --> 00:28:52,620
In other words, if we're searching for octopus

476
00:28:52,620 --> 00:28:54,940
then it has a bunch of categories associated with it.

477
00:28:54,940 --> 00:28:57,920
>> For example, it's an animal, it lives underwater, 

478
00:28:57,920 --> 00:28:59,710
it has a certain body temperature.

479
00:28:59,710 --> 00:29:01,210
I don't know.

480
00:29:01,210 --> 00:29:04,230
And all of these categories are links to other places where you can go 

481
00:29:04,230 --> 00:29:06,640
to see things with that same category.

482
00:29:06,640 --> 00:29:13,450
In other words, the octopus data set would contain a link to the data set for all animals,

483
00:29:13,450 --> 00:29:16,790
and that would let me move around in the database really quickly.

484
00:29:16,790 --> 00:29:21,740
This can be very useful if you're doing something like comparisons.

485
00:29:21,740 --> 00:29:24,490
In other words, given a certain thing, you want to see 

486
00:29:24,490 --> 00:29:27,890
what else it's related to and see what else it's not related to.

487
00:29:27,890 --> 00:29:30,700
That sort of thing. It can be useful in a number of ways.

488
00:29:30,700 --> 00:29:34,250
If you're looking for more of a challenge and to be able to do some more complex things

489
00:29:34,250 --> 00:29:38,740
I would consider taking a look at the Freebase API.

490
00:29:38,740 --> 00:29:44,670
But largely, Wikipedia is a very simple place to go as far as getting information.

491
00:29:44,670 --> 00:29:48,340
Another place that I'll look at is Last.fm, and I'm actually going to go to the site

492
00:29:48,340 --> 00:29:53,800
in case some people aren't familiar, but Last.fm is basically a music

493
00:29:53,800 --> 00:29:57,220
tastes and recommendations website.

494
00:29:57,220 --> 00:29:59,000
You can make an account.

495
00:29:59,000 --> 00:30:04,250
You can start uploading music from your music player

496
00:30:04,250 --> 00:30:08,020
to the website, and basically it will start giving you music recommendations

497
00:30:08,020 --> 00:30:10,030
based on what you listen to.

498
00:30:10,030 --> 00:30:14,270
>> For example, if you go to your profile page—this is mine—

499
00:30:14,270 --> 00:30:18,180
you can see you have a list of recently listened to tracks.

500
00:30:18,180 --> 00:30:22,550
You can see overall favorite artists, all of that sort of thing,

501
00:30:22,550 --> 00:30:25,280
and again, there's a big API behind Last.fm,

502
00:30:25,280 --> 00:30:29,360
 and you can use it to do lots and lots of really cool things.

503
00:30:29,360 --> 00:30:38,870
For example, I'll go to a friend's page who has this Last.fm Tools website.

504
00:30:38,870 --> 00:30:42,380
This is actually another platform that's built on the Last.fm API,

505
00:30:42,380 --> 00:30:45,420
and it does a number of pretty interesting things.

506
00:30:45,420 --> 00:30:50,260
If I log in with my user name, for example, 

507
00:30:50,260 --> 00:30:53,110
I can ask it to generate a tag cloud, for example,

508
00:30:53,110 --> 00:30:56,480
and what that's going to do is give me back an image of

509
00:30:56,480 --> 00:30:59,850
all the different genres and that sort of thing that I like to listen to.

510
00:30:59,850 --> 00:31:01,410
How is it doing this? 

511
00:31:01,410 --> 00:31:05,670
Very basically it's saying to the Last.fm API here's this user.

512
00:31:05,670 --> 00:31:10,710
I'd like to know the genre of every song that they've ever listened to,

513
00:31:10,710 --> 00:31:15,130
and you can do that by making a pretty simple AJAX call to the Last.fm API.

514
00:31:15,130 --> 00:31:18,990
You'll get back a big list, and then obviously some other stuff is being done

515
00:31:18,990 --> 00:31:22,280
to turn it into a word cloud, but you can see overall

516
00:31:22,280 --> 00:31:25,850
it's very easy to access and very easy to use.

517
00:31:25,850 --> 00:31:30,750
Really nice for a number of things.

518
00:31:30,750 --> 00:31:35,940
>> I think that's about all I'll say overall.

519
00:31:35,940 --> 00:31:39,040
One last thing I'll mention about APIs in general is that 

520
00:31:39,040 --> 00:31:41,840
you'll sometimes run into something called rate limiting,

521
00:31:41,840 --> 00:31:44,940
and the idea of rate limiting is you don't want to abuse APIs.

522
00:31:44,940 --> 00:31:48,130
In other words, it's really nice that a lot of these websites have APIs

523
00:31:48,130 --> 00:31:51,070
that you can go to and use for free.

524
00:31:51,070 --> 00:31:54,460
However, if you're making millions or billions of requests per day,

525
00:31:54,460 --> 00:31:57,610
for example, if you're stuck in an infinite loop that's infinitely querying

526
00:31:57,610 --> 00:32:00,680
some sort of API and getting back a huge amount of data,

527
00:32:00,680 --> 00:32:04,570
obviously that's not good, so what a lot of APIs do is have this rate limiting feature

528
00:32:04,570 --> 00:32:09,970
that says you can only make 1,000 requests per day per IP address or something like that.

529
00:32:09,970 --> 00:32:12,540
And if you're doing a lot of testing and that sort of thing, 

530
00:32:12,540 --> 00:32:14,890
you'll sometimes run into that, and suddenly it will shut you off 

531
00:32:14,890 --> 00:32:18,280
and say no, I'm not giving you any more data.

532
00:32:18,280 --> 00:32:20,000
>> What you want to do is play by the rules.

533
00:32:20,000 --> 00:32:22,950
You want to make sure that you read the API spec carefully.

534
00:32:22,950 --> 00:32:26,330
If it has certain rules attached to it, like you can only make X queries per day

535
00:32:26,330 --> 00:32:30,000
or you can only access a part of the database a certain number of times 

536
00:32:30,000 --> 00:32:32,900
or something like that you want to make sure you stick to that.

537
00:32:32,900 --> 00:32:38,360
As long as you play within those rules you'll probably have a really nice time using APIs.

538
00:32:38,360 --> 00:32:42,030
Your overall takeaway is APIs are really, really useful.

539
00:32:42,030 --> 00:32:45,610
>> There's an API for almost any big web service out there.

540
00:32:45,610 --> 00:32:50,700
Pretty much any part of the Google Tools Suite, Google Maps, Google Earth,

541
00:32:50,700 --> 00:32:54,390
GMail, Google Calendar, all of those things have APIs.

542
00:32:54,390 --> 00:32:58,280
You can use them to both get data from the server and send data to the server.

543
00:32:58,280 --> 00:33:00,870
In other words, if you wanted to make a calendar app that can update 

544
00:33:00,870 --> 00:33:04,190
someone's Google Calendar, there's an API for that.

545
00:33:04,190 --> 00:33:07,810
If you want to make something that's going to tell you where 

546
00:33:07,810 --> 00:33:12,530
the location of a certain address is you can use the Google Maps API for that.

547
00:33:12,530 --> 00:33:15,860
APIs are fantastically useful, and they're everywhere.

548
00:33:15,860 --> 00:33:18,700
If you're interested in some sort of idea, 

549
00:33:18,700 --> 00:33:22,170
there's probably a related API that you can use to get a lot of data 

550
00:33:22,170 --> 00:33:25,060
very quickly and very simply.

551
00:33:25,060 --> 00:33:28,140
>> If you're still looking for a project or if you just want to play around 

552
00:33:28,140 --> 00:33:31,820
with something in general, APIs are definitely worth doing.

553
00:33:31,820 --> 00:33:37,200
Thanks, and I'm happy to answer any questions that you guys may have.

554
00:33:37,200 --> 00:33:44,900
Okay, thanks a lot.

555
00:33:44,900 --> 00:33:48,000
[CS50.TV]