 Students, we have been discussing about the relational model. It consists of tables, it consists of the relationship between the tables and so on, about the entities, the type of relationships, the cardinality and so on. So, in this slide and in the subsequent slides and in this model, I will be talking about what is the relational model itself. The relational model is based upon Edgar Codd's rules, 13 rules, 0 to 12, they are numbered. He is considered as the father of the relational model. What he has described is the perfect relational model and there are hardly any products in the market which follow all those rules to the letter and spirit but it defines the relational model and banks, financial institutions, big organizations, airlines, industries, they are working based on that relational model. It's a robust model so what I will do in this module is to briefly go over those rules of Codd and in the next module I will explain those rules using some simple examples. Let's start with those rules. This is the foundation rule, rule number 0. This rule must be applicable, it has to be there for a database model to be relational model. This is mandatory rule, it is understood, this is by default. What it is saying that whatever it is stored, that is stored in the tables and whatever tables are there in the database, they are related, there are no independent tables. Independent means there are no floating tables. It means that every table is associated, is related with at least one table. There are no independent or floating tables and their permissions. Of course the administrator has a lot of all the rights, the permissions are assigned to insert, to update, to delete on those tables and how is this performed? This is performed using a query language which could be SQL and all the subsequent rules, the next 12 rules they are based upon this rule number 0. Now let's briefly go over those rules. The information rule, the information rule states that the data which is stored in a database that will be stored in a table, it will be stored in a cell. What is a cell? A cell is a cross section of a row and a column. It will be stored there, more details in the next module. Guaranteed access rule, it means that the concept of primary key which I have already discussed that using the primary key, using the table name and the desired column, I should be able to get what I want. That is the guaranteed, it is guaranteed, should be able to get the data that of course this rule, the rule number one, they are implemented in all the relational models. Systematic treatment of null, what is a null? It means that if something is unknown, if something is not applicable, if it's missing, there should be a consistent and systematic representation. The data type is irrelevant, that I will explain in the next module. Then is the rule active online catalog, active online catalog means that in my working space I have multiple tables, tables have their columns which are the attributes, they have their constraints, their relationships, their indexes, all that information is again stored in a table and the people with the right rights, they are able to curie that table and retrieve the data, that is the active online catalog. This is like a data dictionary or the metadata, data about the data itself, comprehensive data sub language rule and I will use the same language to access that dictionary, the language which I have been using to access the standard tables, view updating rule, I generate a representation of the tables that is a view and when I change the view, the table should be changed. This is kind of a tricky thing. However, if I change the table, the view change, that is kind of straightforward. High level insert, update and delete rule, so this can be performed at a high level. It means that I don't go as a detail, I can do it for 10, 100 or 1000 records. I should be able to do that. Physical data independence, it is irrelevant whether my data is stored on the type of hard disk or on multiple hard disks or how it is indexed, that is irrelevant. That is the physical data independence, logical data independence, logical data independence and logical data independence. Basically, in this context is that my data is stored on two tables, which is vertically split or it is stored on multiple table horizontal split or it's a combination. To me, it appears as a single table, as a user, as a programmer, integrity independence, whatever changes are being made, those changes must be made to the QD language. No other shortcut, no other way, no, if that is the case, it's a violation. Distribution independence, this is, it is irrelevant where my data is stored. I am in country one, my data is in country one, part of in country two, part on continent three, on the server, on the cloud is irrelevant. This is the basis for the distributed databases and finally non-subversion rule. There should be no backdoor, there should be no secret entry point, there should be no other thing to change the contents of the database other than the language being used. That's all. I will explain these points with examples in the next module. Thank you very much.