 So, in this module, I will talk about how you design a database that is called as entity relationship modeling or this is the design it will cover the steps and the processes very very briefly which are there when we design a database application. Of course for a web-based database application we have to take into consideration other aspects also. In addition to ER modeling entity relationship modeling, I will also cover 12 rules, 12 rules which are about called as the CODs rules and those 12 rules are about the relational model which we will be discussing throughout this course. Relational model is how the database application is developed and what is at the back end I have discussed very very briefly with you the layer in the previous module. So what is an entity? Entity can be something which is important to a business for an application it could be something which is which is living thing it may not be living thing for example, a living thing like a student or a non-living thing like a course or like a lecture room and so on or like an automobile also so entity is something which is of importance to the business entities can be collection and these are those things without which the business doesn't make any sense so these are the important ingredients of a business of an application that is an entity and entity has attributes attributes are the properties for example a student is an entity a course is an entity the attributes of the student could be and are the name of the student the address of the student the GPA of the student the courses which the students the takes that is related to the course taken that is the relational aspect which I will cover so let's very very briefly look at some of the type of attributes for example we have the simple attribute or the atomic attribute it means that if I break the attribute divided into parts it doesn't make any sense then I can have the composite attribute also which is the attribute which is created by combining the properties from multiple attributes that is the composite attribute then I have called as the single valued attribute such as the social security number or as the NIC number that attribute has a unique value a person doesn't have two social security numbers or two ID numbers so that is the single value attributes then are the multi-value attributes say for example the cell numbers a person can have multiple cell numbers and a person can take multiple courses also those are the multi-valued attributes and then I have the entity keys set keys so I have the super key which is a set of attributes then I have the primary key a primary key is a unique and it doesn't repeats itself and I can identify an entity based upon the primary key and of course I have the candidate key also so the most important key over here is this primary key for this is used for the identification purposes and this is also a single value thing you see over here though this is also unique so now let's look at how the things tie together and we go through the cardinalities the cardinality mean over here it is the size basically it is the size of the set so one to one relationship is a type of relationship say for example the car of the CEO can be parked at the spot which is reserved for the CEO that is a one-to-one relationship so the CEO car will be parked over there and no other car can be parked over there so of course then there are one to many relationships and many to many relationship also over here so this is the type of relationship say for example a student can take multiple courses and a course can be taken by multiple students I will go into all of these details so we have the entity we have the attributes and we have these cardinality relationships in an ER model so when we tie together all these things so what we have this diagram in front of you so I have this entity over here entity you can call it entity one you can call it entity two and this this entity one say for example has attribute one and attribute two and of course this also has attribute one and attribute two and this is the relationship which ties together these entities it ties together these entities now I can assign values to these attributes and to these entities you can see over here so the name is an attribute the gender is an attribute and of course the course is an entity and there are attributes of the course also so with this now I move on to something which is called as a 12 rules the cards 12 rules now these 12 rules are by the famous you can call him a mathematician or you can call him the relational modeler who did who developed the relational model so I will briefly go over these 12 rules of code and when we go to the detail of this lecture I will talk about these rules in detail and I will also give you examples of those rules so first is the information rule the information rule in simply states that the data is stored in a table and by the basis upon the rows and column I can access the data and I can use the primary key to access to get what I want then is the guaranteed access rule it means that I can get what I want and there is no hindrance to it and the accessible data is there in the table systematic treatment of null this is very interesting because if the data over there is missing if the data is not available or it is not applicable then you cannot leave it empty to put a zero over there so it is what we are saying over here is missing it is not applicable or it is not available it is not available okay that is the case over there active online catalog so the way we have data stored in the tables the same way we have the data about the tables stored as tables comprehensive data sub language rule it means that we have a language also which is the sequel and of course these are 12 rules and we cannot go over all of those rules in detail in this module but I promise you that I will go through them in detail in the module when it comes