 So, in order to understand how databases work on the internet, we need to understand what internet is. We need to understand how internet works. We need to understand what are the different mechanisms of exchanging data over the internet. All of this will help you better understand and better develop the web-based database applications. And it will help you understand the issues and how to take care of those issues to be a successful web-based database application developer. So, when you are chatting with somebody, your friend using your phone, smartphone or using your computer and your friend is also using a smartphone or a computer at the other end maybe at other part of the world. So, in between there are maybe a dozen or so computers which are bridging that gap between yourself and between your friend. That network of computers, that group of connected computers, those computers which bridge the gap running the TCP IP protocol, those computers running those protocols over a telecommunication network, that network is the internet. Internet is like a network of roads. It is like a network of telephone lines. It is like a network of electrical wires in a building. So, over the network, the traffic flows. In the context of roads, over the road network, vehicles move. In the context of telecommunication network, calls are moving and so on. So, internet is just like a network. Of course, it is a network of networks. It is a network of networks and it is running the TCP IP protocol which I will discuss in more detail. So, I believe up till now you have gotten the picture. So, this lecture or this module will consist of two parts. One part is this, the other part I will tell you totally. So, in this module, I will talk about what is internet and what internet does. So, when I say what is internet, of course, I will explaining to you how internet works very, very briefly because the more details are in the next module which is how data moves on the internet. And very briefly, there are two methods of using or moving the data which is the circuit switching and packet switching. I will go into a lot of details. The circuit switching is between the two points, a path is set. It is dedicated to be exclusively used by person A, person B, computer A, computer B. That is circuit switching. Packet switching is that the data at A and B is divided into packets which can use different paths, routes over the internet and arrive at destination may be lost during the process also and resend and reassemble and generate the message or whatever. And how computers do different jobs on the internet. So, that is part of the next module. So, let us now go into what is the internet. So, internet is a global system of interconnected computer, interconnected computer networks. It is a network of networks not of road networks but a network of computer networks which share the same protocol which is the TCPIP protocol. And of course, this protocol may be a supporting non-computing devices also because now we have something called as the IoT internet of things. We have sensors, we have different things which are also connected over the internet. So, the primary precursor of the internet is ARPANET. The ARPANET was developed in the 1970s to connect the university campuses and the defense establishments in the United States and that ARPANET formed the backbone of the interconnection in the 1970s. And then it evolved over the period of time and Vincent Cerf is the inventor of you can say is the inventor of internet. So, as I discussed earlier that because of the software architecture evolution and the revolution what has happened that I will discuss in the next slides you see that we have this network of networks and I have this machine over here this machine over here and I have this connection over here it can be a dial up connection over here I have the service provider and of course I can communicate with this device also from here to here or from here to here and so on. So this is what internet is. So, there is no central body, there is no established structure because these links these links can go down also, these links can go down also and maybe new links come up also and so on. This is what internet is. So what I was discussing that because of the architecture software architecture because of the proliferation and so many things there has been a tremendous adaption of the internet and you can see that there is almost an exponential rise in the number of countries which are getting online and we can see that about 210 countries getting online in about 20 years. So that is a lot of countries in a very small amount of time. Now this adoption of internet is not limited to rich countries but also not so rich countries also as shown in the next slide as you can see over here roughly more than half of the world population over here. They don't have kind of internet access in 2015 right or not in terms of percentage in terms of percentage per whatever right or not. So the point over here is that there is a divide over here between the have and have nots a digital divide. So of course it takes money it costs money but the point is still there has been a tremendous proliferation of internet. Now let's briefly look at what internet does so very very basically internet moves data. Now what data it can be audio it can be video it could be text it could be anything else it could be combination also when we say data it means digital data. So as the traffic moves cars move over a traffic network or a road network data moves over the internet that's one purpose of internet internet is like a postal service meaning that the data moves from one point to other point the responsibility of the postal service is to ensure that the letter is delivered at the given address they are not concerned about the contents of the letter as long as the certain tickets are on that envelope they are not concerned about the contents as long as it's paper same as true for the internet. The big difference is that postal service is governed by certain rules regulations owned by the government but internet is decentralized so it's not totally like a postal service. It is neutral to data as I told you before that data could be any data it is just ones and zeros it could be audio it could be video it could be a combination it could be email it could be chat messages whatever and finally it is neutral to applications I could be running any application as a matter of fact let me give you an example of Skype. Now Skype was developed by two European developers okay they didn't had to change internet they didn't have to change any protocols they developed Skype on top of the internet protocols they developed Skype on top of the standard internet that is one example of openness of internet also and another example of neutrality of applications over the internet Skype using internet then WhatsApp using internet and of course there will be many more applications to the benefit to our benefit okay which will be running on the internet because internet is neutral to applications that is one purpose of internet thanks for your time.