 So in this module, we'll talk about the database connectivity and you can see on the slide the aspects of database connectivity, which we'll be covering over here. And I'll also talk about the two tier model, I'll also talk about the three tier model. And this module, I will also give you a comparison of web based application and an application which of course is a non web based application. And I will also very briefly talk about different programming languages for the web. Of course, this material is with reference to the main stuff, this is just an introduction to give you an idea what is going to come. So the basic concepts, we have internet, we have the intranet, we have the extranet, and we have HTTP, we have TCP and IP, and there are different protocols also intranet is the network which is internal to an organization and extranet is the people from outside are allowed to access that intranet and then are the web based architectures. And we see that the different layers over here, the browser layer is the client itself and then is the web application logic layer where the application is built. And that is the layer, which takes a lot of effort, which takes a lot of time and expertise of the programming. And then of course is the database layer where the data is actually stored. So we will be covering all those aspects from different angles. So let's move on and we see the comparison between traditional client server application and a web based application. I will briefly do go through the comparison, the details are in the material when we go to that point. So the first over here is the platform dependent, platform dependent and the web application is platform independent because it is running in an environment which supports independence. It is not tied to a certain architecture. It is not tied to a certain operating system. It is not tied to a certain model. Of course, it covers the three tier architecture, the client is natively compiled and has fast execution speed because the application is running on the client. It is the application is running where you are actually using it. But the over here, the client is an interpreter and it is slower. For example, JavaScript JavaScript is not compiled, it's not binary. So it runs slow, it has to be interpreted. So it cannot match the binary speed of a compiled installation is necessary. If I want to use an application, for example, to write a letter or to do my accounting, then I have to install that application, but no need for installation for a web based application. The complex client high maintenance cost, but for a web based application, the maintenance is taken care by the internet service provider, by the database service provider. And it is their responsibility. So we go over three new unfamiliar interface for the users. For the web based application, it is a familiar application. It is a familiar interface and the GUI constructs are custom ones add to the download time. But over here, the download time is not there. The reason being that the client application, the server application, they are not running over the web. They are able to integrate with existing applications. Why? Because the applications don't talk to each other. But by default, by design, the web based applications have to talk to each other. Therefore, they are easy to integrate. And finally, this is the persistent connection to the database, non persistent connection. Web is a stateless when we make a connection, during that connection, the data transfer takes place, the query goes there and I get the results. But that connection is gone once I have made the request and my request has been fulfilled. So this is these are some of the main differences. And I hope now it will be clear to you that how the traditional client server application differs from a web based application. So web based database architectures are two tier client and the three tier client servers architecture. Now in a two tier client, we have what we call as the used to be the dumb terminal or I have a PC and that PC connects to my server and I have the application running on part of the application is running on the client and the main part is running on the server. There is nothing in between. So I have this client, I have the server, the client makes a request, say for example, you know the status of the my customer, the transactions made by my customer. So I make a request to the server. The server has this database running over there and I get the results. I get the answers. So that is a two tier architecture and I am running it on my machine in a in a kind of the environment which I showed you in the previous slide. Now for the three tier architecture, I have the client, which is the browser, which is my machine, which could be my cell phone. And then of course, I have the other in between layer, which is the web server, which is generating the pages for me. And then I have this database server. So the request goes to the database server, the database server sends the data and the web server generates a page using that data. And I have this thing, the data represented, presented to me. Now you might have seen that sometimes when you access a website or a web application, you see kind of the junk, actually it's not junk, what had happened or what is happening is that the web server had crashed. So the there was no generated HTML. So the commands of that web programming language were visible to you. So over here is a brief explanation of the three tier architecture, which explained to you. So this is the client. This is the first tier. And this is the web server. This is the second tier. And the PHP scripts are running over here. The Apache server is there. And this is the third tier where I have this my SQL database server available to the data is. So I make a request, the request goes over here, the request goes over here. I get the answer. It generates, it generates the web page. And this web page is displayed to me over here. So this is the three tier. This is the three tier architecture, okay. Now we can see that this is one way of looking at the things. And then I have this client side solution and server side solutions. Now the client side solutions take into consideration the processing power of the client. And these client side solutions, they can be not completely done for a web-based application. And the server side solutions are there. So it's a combination, database, gateways. And then I have the browser extensions in the JavaScript, then Java, ActiveX and external applications. All of these are at the client. It makes my application work better, look better, perform better and more productive to me. And of course, these are the things which I have to discuss. And finally we have this gateways. And that's all about this in this module.