 So, now we will talk about what is a database. I will define a database value. Of course, you may have heard what a database is and you may have read what a database is. Now I will be talking of a database in the context of web-based database application. And I will also describe what a web is. And I will show you that although a database and a web, they are developed by people with different backgrounds in terms of education, in terms of their professional background. But there are a lot of similarities between a database and a web. And those similarities need to be capitalized when we are developing web-based database applications. So let me go over these points one by one. So databases handle large amounts of structured data. This is the point. Now, if I have to manage something, and it is for my individual level, then maybe I can do it on a piece of paper, right? But if I'm doing it for my class, for my department, for my university, then of course, I am looking at large amount of data. So that's why the databases are there. And the data is structured so that it fits in nicely in the structure or the format for which the application is designed. Now remember one thing. Some people call a collection of data as a database. Some people call an application which is used to develop, say, accounting system as a database. And some people call the application which is developed for this purpose. So data then may be oracle or informus and then is the accounting application. Databases can change quickly and unpredictably. Now, if you consider the case of a class, the students who register in a course, maybe one or two students drop out, maybe one or two students add up. But that is not the case for the visitors who are coming on a website. There are millions of visitors who are coming on a website. They may or may not be repeat visitors. So the point I'm trying to make over here is that unpredictably, the amount of data can change. Databases, data needs to be selected and displayed in different ways. For example, I would like to see my customers based upon their age, based upon the how long they have been with me, based upon their geographic location. So I would like to see the data displayed in different ways. Then of course, there are tools. This point over here, which are used to manipulate the data. The programmer should not be spending lots of time writing low level code to extract data to generate those figures. So the programmer should be working on more productive tasks. And databases contain metadata. Metadata is the data about the data itself. How many tables are there? What are the names of the attributes? It is gender or it is sex or what are the type of the data type? The age is stored as an integer. The age is stored as a real number and other figures also. Databases contain validation and integrity features. So once the data goes into the database, only using the right privileges and using the certain language, one should be able to change the contents of the database. That is the data integrity. That is the data integrity and the data validation is that if I am entering some unique data as a primary key or the ID or the customer ID that is unique, then that uniqueness should be validated at the entry point. Databases are often shared across time and space. That is the purpose of a database in a global environment in the web that is there. And of course, the data can be related to one another. The point over here is that if I have the customer data, then I can have the transaction data of those customers in a database, not the inventory data. That may not be very much related. And of course, databases contain multiple instances of similarly structured data. I have the data about my customer who has been purchasing different items. So I have other customers who are purchasing other set of different items. So they are all related. Databases can be normalized. Normalized means that I need to convert. I need to store the data in a certain way such that it can be accessed efficiently. It can be accessed quickly. There are no anomalies. There's a space, sewage, and so on. Now, if you look at the web, right, we can see that there are many similarities in the web as compared to the database, not as opposed to a database, but as compared to a database. Large amounts of data is handled. That is the purpose of creating the web which was created in 1960s, connecting academia, connecting research organizations, connecting defense organization. And it has to be displayed in different ways. Now metadata is also there, which is the data which you don't see. And finally, the purpose of the web was to share the data, and that is the purpose why we develop web-based database applications.