here model has been used for past many years in order to represent his design this database maybe if you are comfortable with or if you have gone through these you know uml model set based ones you can easily relate this in your mental diagrams you have something called as class right so exactly like that we have with now I know your diagrams it is like this in software design know the way UML diagrams are going to play the role in database design your diagrams are going to play the role of it and various things in our you know your diagrams are one is called as entity so here itself means entity relationship model right ER model means entity relationship model product and in this entity relationship model they are actually you know three things that you should know one is called as entity okay and the other is called as the attributes and the other is called as relationships okay so why do we generally use this ER diagram just to write in terms of pictures what is the information we collected just like this software design first we are going to collect the requirements which means we go and talk to the people like what do they want and now they are going to say in words you know they are going to describe what they need then we are going to convert their that I know word description of their needs into this diagrams right and now in the in whenever they speak of something whenever they say their needs there are going to be nouns and the nouns are nothing but the things are the object for example they say person or car or or in a board whatever so every object is nothing but an entity so now when they talk about it when they speak about it when you collect the requirements the norms are going to be the entities alright and then works walls are going to be relationship let us say a person who owns a car right owns work that is going to be relationship right or if a employee works for a department works for that is going to be relationship right so now an entity is nothing but any object in your database is going to be an entity right and a relationship is nothing but any verb which you are going to describe is going to be a relationship and what about attributes attributes are again nouns which describe these nouns for example a person if he is an entity then he is going to have attribute like this he is going to have a name he is going to have some A's and you know he's going to have an address right phone number so all these are going to be the attributes right so now entity is nothing but you can think of it like a thing right a thing in our real world which is going to be recorded in our database right and that is what is called as entity and what is an attribute is attribute or nothing but the properties of the entities or in order to better describe the entity we are going to use attributes right so you can think of it as properties properties which are used to better describe these things all right for example you can think of a entity as a person right and then how do you describe a person may be using name right and is and address phone number all this okay and what is relationship is you can think of relationship as association among entities how are these things related that is called as a relationship how is a car related to a person a person owns the car right or how is the department related to a employee if the employee works for the department right and this is called as relationship relationship is nothing but what is the association among these entities right so it is going to talk about Association right for example what is the association between employee and a department works for so works fur is a relationship all right so we have all these three things which have to be discussed in detail in in case of we are diagrams okay so coming to this er diagrams the terminologies like this you know we are going to use set theory here in the sense we talked about in tt type and entity attribute it is okay and relationship type and relationship okay now what is entity entity and entity type is we are going to talk about these two things generally entity type right and entity okay so what is entity type is the name or the heading or the schema schema is nothing but the heading for example if I say person person is entity type who is having attribute is name and let us say address okay now this entire thing is called as entity type entity type will describe the heading right it is also sometimes called as schema so schema is nothing but the description the heading right and what about the entity entity is nothing but a person who is going to be represented in this entity type itself for example let us say name is is you know 26 and name is some Raju right and let us say address is some address is given now this is called as entity so entity is actually an instance and entity type is the heading right now sometimes it is also called as intention and it is called as extension so if you want to think of it as a set theory right this entire set the name of this set is called as entity type and the elements in this set they are called as entities right and we are not going to change entity types but then we might add and delete some elements into the entity type right therefore entities they make added or they might get you know deleted and at any time the number of elements are all the elements in any entity type is called as state state of the entity state of the generality is also called as if I put all all of them together state of the database what it so even though this is quite you know it is used but then generally people will call an entity type as an entity and entity as an indica type so they are going to use them as if there is no difference actually there is difference for you entity type means just the name and identity means the instance right so in some questions you might have to observe the difference and in general whenever you know we speak in during the explanation and sometimes use entity and on sometimes use entity type then you don't get confused from the context it will be clear what it and the same things will apply even for relationship also all right relationship type and the relationship itself so relationship means it is actually an instance and relationship type means what is it's heading schema right so schema is nothing but the heading the you know how do you represent it okay and now in your diagrams we don't use really entities we use entity types which means we don't really show you everything that is present in the database we don't we don't write a set diagram and then we don't put a point for every element present in it we are going to represent it in a shortcut just using the entity types therefore if you look at any air diagram you are going to only see the schemas the headings right not how many elements are present in this and not any set diagrams we are going to make it you know keep it as simple as possible the main intention of this diagram is to help the communication between the technical designer of the database and the neighb user who does not know anything about database he is just going to say in words and you are supposed to capture those nouns works and you are supposed to put them in the diagram and a refinement has to go on and for the refinement to go on you have to sort your suppose to show this diagram to again the users and they are going to say see this part has to be improved or you know this entity is going to have even more attributes or they might even say some constraints that you are again supposed to capture and then and again refine it for it so this is actually a cycle this cycle goes on for some time okay so then what happens is once we are done with this diagram representation then we are going to the next level so if you remember it we are talking about the conceptual design right so one once we are done with the conceptual design then we have to go with the representation right then we have to go with the you know physical representation so now we are here talking conceptual design next we will go for the representational design so now we are going to use here diagrams later we are going to use relation tables which means later we are going to take this air diagrams and convert them to the relation tables and later we are going to take the relation tables and we are obviously going to store them on the hard disk right implementation so now we are going to look at this let us see in depth about each one of this right once you understand them well then the conversion of these into our diagrams into relationship tables is going to be straightforward okay
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