1 00:00:00,450 --> 00:00:05,160 -: So we talked about the basic principles of what is an API 2 00:00:05,160 --> 00:00:08,460 but another thing that is important to know about API 3 00:00:08,460 --> 00:00:10,890 is that it comes in few flavors 4 00:00:10,890 --> 00:00:14,193 and actually there are four main types of API. 5 00:00:15,060 --> 00:00:20,060 The first type is Operating System API, next Library API 6 00:00:21,540 --> 00:00:26,540 then Remote API, and last, Web API. 7 00:00:27,270 --> 00:00:28,920 Let's dive deeper into each one of them 8 00:00:28,920 --> 00:00:30,663 and explain what is it. 9 00:00:31,560 --> 00:00:33,900 So Operating System API. 10 00:00:33,900 --> 00:00:36,420 Let's say you write some kind of application. 11 00:00:36,420 --> 00:00:38,460 It it doesn't really matter which platform 12 00:00:38,460 --> 00:00:40,260 you are using to write this application 13 00:00:40,260 --> 00:00:43,860 it can be .Net or Java or c++ or whatever. 14 00:00:43,860 --> 00:00:46,380 Now, naturally, your application runs 15 00:00:46,380 --> 00:00:48,270 inside an operating system. 16 00:00:48,270 --> 00:00:51,300 Again, it doesn't matter which operating system. 17 00:00:51,300 --> 00:00:55,293 iI could be Windows or Linux or OASIS or anything else. 18 00:00:56,460 --> 00:01:00,870 In many cases, the application needs some kind of services 19 00:01:00,870 --> 00:01:02,790 from the operating system. 20 00:01:02,790 --> 00:01:05,099 For example, file system. 21 00:01:05,099 --> 00:01:08,370 If the application wants to access files 22 00:01:08,370 --> 00:01:11,970 in the operating system, it asks the operating system 23 00:01:11,970 --> 00:01:15,150 to give it access to the files. 24 00:01:15,150 --> 00:01:17,040 Network devices. 25 00:01:17,040 --> 00:01:19,950 If the application needs to access network devices 26 00:01:19,950 --> 00:01:21,930 connected to the operating system, 27 00:01:21,930 --> 00:01:24,960 then the operating system should allow it. 28 00:01:24,960 --> 00:01:26,520 User interface elements. 29 00:01:26,520 --> 00:01:29,880 If the application, for example, wants to display a button 30 00:01:29,880 --> 00:01:33,060 on the screen, then it asks the operating system 31 00:01:33,060 --> 00:01:36,000 for a visual representation of the button. 32 00:01:36,000 --> 00:01:37,950 So how does it do that? 33 00:01:37,950 --> 00:01:41,070 How the application asks the operating system 34 00:01:41,070 --> 00:01:43,230 for all those kind of services? 35 00:01:43,230 --> 00:01:45,360 Well, the answer, as you probably guessed 36 00:01:45,360 --> 00:01:48,030 is using the operating system API. 37 00:01:48,030 --> 00:01:51,750 The operating system or the operating systems 38 00:01:51,750 --> 00:01:53,550 exposed some kind of API 39 00:01:53,550 --> 00:01:56,670 that applications that run in the operating system 40 00:01:56,670 --> 00:01:58,110 can access and use. 41 00:01:58,110 --> 00:02:01,189 And one of the most famous operating system API 42 00:02:01,189 --> 00:02:03,330 is the win32 API. 43 00:02:03,330 --> 00:02:07,110 It is used by all the applications that run on Windows 44 00:02:07,110 --> 00:02:10,893 and it provides a huge number of operating system services. 45 00:02:12,630 --> 00:02:14,040 Okay, next. 46 00:02:14,040 --> 00:02:18,570 So the next type of API is the Library API. 47 00:02:18,570 --> 00:02:20,550 And what it means is this. 48 00:02:20,550 --> 00:02:22,470 When you develop your application, 49 00:02:22,470 --> 00:02:24,960 you probably use some kind of libraries. 50 00:02:24,960 --> 00:02:27,270 The concept of libraries is very common 51 00:02:27,270 --> 00:02:29,880 in all the development platforms today. 52 00:02:29,880 --> 00:02:33,540 So you develop your library, let's call it Users library, 53 00:02:33,540 --> 00:02:37,350 and there is another library called Logging library. 54 00:02:37,350 --> 00:02:41,550 Now the user library wants to use the logging library. 55 00:02:41,550 --> 00:02:42,870 How can it do that? 56 00:02:42,870 --> 00:02:47,870 Simply, the logging library exposes logging API, 57 00:02:48,150 --> 00:02:51,840 and by doing so, it allows the user's library 58 00:02:51,840 --> 00:02:56,130 to access this API and use logging library's method 59 00:02:56,130 --> 00:02:59,820 such as right to log file or change the severity 60 00:02:59,820 --> 00:03:02,100 of the logging or anything else. 61 00:03:02,100 --> 00:03:04,530 But without an API, the users library 62 00:03:04,530 --> 00:03:07,140 won't be able to access the logging library. 63 00:03:07,140 --> 00:03:10,080 Now note again that those libraries 64 00:03:10,080 --> 00:03:13,860 they are both executed in the same single process. 65 00:03:13,860 --> 00:03:16,953 They are not communicating through any kind of network. 66 00:03:18,240 --> 00:03:21,780 As mentioned earlier, class libraries are implemented in 67 00:03:21,780 --> 00:03:24,060 all kinds of development platforms like 68 00:03:24,060 --> 00:03:27,600 as we said, .NET, Java, Python, nodeJs 69 00:03:27,600 --> 00:03:30,453 and even PHP and so on and so forth. 70 00:03:31,470 --> 00:03:36,470 Okay, so the next type of API is Remote API. 71 00:03:38,400 --> 00:03:41,940 Now what it means is this, we have two software components. 72 00:03:41,940 --> 00:03:45,840 Let's say these are User component and Orders component. 73 00:03:45,840 --> 00:03:48,390 Now note that those two components 74 00:03:48,390 --> 00:03:50,310 are distributed over the network, 75 00:03:50,310 --> 00:03:52,890 meaning they are not in the same process 76 00:03:52,890 --> 00:03:55,530 and probably also not on the same server 77 00:03:55,530 --> 00:03:58,110 or virtual machine or PC. 78 00:03:58,110 --> 00:04:00,390 In order for them to communicate with each other 79 00:04:00,390 --> 00:04:02,580 they need to go through the network. 80 00:04:02,580 --> 00:04:03,730 So how do they do that? 81 00:04:05,371 --> 00:04:09,000 So the User component build an Orders proxy. 82 00:04:09,000 --> 00:04:12,060 This proxy is used to communicate with the Orders component. 83 00:04:12,060 --> 00:04:15,150 This proxy contains all the internal working 84 00:04:15,150 --> 00:04:17,010 of accessing the Orders component. 85 00:04:17,010 --> 00:04:19,380 It knows everything there is to know about 86 00:04:19,380 --> 00:04:21,899 how to access the component, such as 87 00:04:21,899 --> 00:04:25,410 network protocol, network address, methods, signatures, 88 00:04:25,410 --> 00:04:28,380 authentication, authorization, everything that is important 89 00:04:28,380 --> 00:04:30,720 in order to access this component. 90 00:04:30,720 --> 00:04:33,660 So after building this proxy, the Orders proxy 91 00:04:33,660 --> 00:04:37,830 can access the Orders component using proprietary protocol 92 00:04:37,830 --> 00:04:39,450 and access the method 93 00:04:39,450 --> 00:04:43,290 and all the other functionality exposed by this component. 94 00:04:43,290 --> 00:04:44,940 Now, what is important to know 95 00:04:44,940 --> 00:04:48,720 about this method of communication, the remote API 96 00:04:48,720 --> 00:04:50,610 is that in it mandates 97 00:04:50,610 --> 00:04:52,470 that both the components will be based 98 00:04:52,470 --> 00:04:55,470 on the same development platform. 99 00:04:55,470 --> 00:04:58,410 For example, it's not possible in this example, 100 00:04:58,410 --> 00:05:01,200 that the user component will be developed using .net 101 00:05:01,200 --> 00:05:03,960 and the orders component will be developed in Python. 102 00:05:03,960 --> 00:05:06,090 It'll simply won't work. 103 00:05:06,090 --> 00:05:10,350 Examples of such a Remote API implementations are 104 00:05:10,350 --> 00:05:15,150 DCOM, .NET Remoting, Java RMI, and there are some more. 105 00:05:15,150 --> 00:05:17,040 Its also important to note that 106 00:05:17,040 --> 00:05:19,170 Remote API is losing popularity 107 00:05:19,170 --> 00:05:21,903 and almost no one is using them nowadays. 108 00:05:22,740 --> 00:05:25,620 And that brings us to the last 109 00:05:25,620 --> 00:05:29,310 and definitely not the least kind of API, 110 00:05:29,310 --> 00:05:31,620 which is the Web API. 111 00:05:31,620 --> 00:05:35,340 With Web API, web apps and web APIs 112 00:05:35,340 --> 00:05:38,460 can communicate with each other over the internet 113 00:05:38,460 --> 00:05:40,410 and here is how it works. 114 00:05:40,410 --> 00:05:42,600 So we are looking at the internet 115 00:05:42,600 --> 00:05:44,760 and we have some kind of web app 116 00:05:44,760 --> 00:05:47,070 which we developed and published over the internet. 117 00:05:47,070 --> 00:05:51,060 This web app wants to use another web apps, let's say 118 00:05:51,060 --> 00:05:54,030 weather web app, which provides weather forecast 119 00:05:54,030 --> 00:05:56,009 for destinations that we are interested in. 120 00:05:56,009 --> 00:05:59,793 How can my web app communicate with the weather web app? 121 00:06:00,720 --> 00:06:02,550 So there are a few steps for this. 122 00:06:02,550 --> 00:06:06,840 First, the weather web app should expose, and again 123 00:06:06,840 --> 00:06:09,600 not the use of the word expose. 124 00:06:09,600 --> 00:06:11,973 It exposes Web API. 125 00:06:13,680 --> 00:06:17,400 Then my web app can access this web API 126 00:06:17,400 --> 00:06:19,950 and it can do it because the web API 127 00:06:19,950 --> 00:06:23,580 always uses standard protocol for accessing it. 128 00:06:23,580 --> 00:06:27,810 And using this protocol, my web app can access this web API 129 00:06:27,810 --> 00:06:31,530 and query the weather web app for weather forecast. 130 00:06:31,530 --> 00:06:33,810 Now, one of the most important thing to know 131 00:06:33,810 --> 00:06:37,110 about the web API is that it can be used 132 00:06:37,110 --> 00:06:40,980 across any platform, operating system, or language. 133 00:06:40,980 --> 00:06:42,030 In other words, 134 00:06:42,030 --> 00:06:44,843 it doesn't really matter how my web app is implemented 135 00:06:44,843 --> 00:06:47,580 and how the weather web app is implemented. 136 00:06:47,580 --> 00:06:50,340 If you remember, we say that we Remote API, 137 00:06:50,340 --> 00:06:53,250 both the software components must be developed 138 00:06:53,250 --> 00:06:54,810 using the same platform. 139 00:06:54,810 --> 00:06:57,270 This is not the case with Web API. 140 00:06:57,270 --> 00:07:00,810 In this example, my web app can be developed using .NET 141 00:07:00,810 --> 00:07:03,930 and the weather web app can be developed using Java 142 00:07:03,930 --> 00:07:05,700 and it'll work just fine. 143 00:07:05,700 --> 00:07:08,850 This is just one of the factors that make Web API 144 00:07:08,850 --> 00:07:11,433 so successful and so popular.