 So, students in this module, we will look at the nuts and bolts of an online advertisement system. So, we will look at the logical model of an online advertisement system and we will also look at the physical model for an online advertisement system. The background for that online advertisement I have already given to you in the prior module right and some of the definitions one or two I will briefly share with you. So, let's dive into this module. So, we will look at the conceptual model. Conceptual model is the concept behind is okay. It is how the things are being viewed at a higher level of abstraction, higher level of abstraction, how the things are viewed at the level of the managers of the decision makers who are not going into the nitty-gritty details of the system implementation. As a matter of fact, they are not required to go into those details. It is not expected out of them. Okay. So, we will look at that higher level of the abstraction and in this logical data model that will be the from the perspective of creating a web based database application. We will look at the tables. We will look at the different keys which are there in the tables. What are the attributes which are important for that application with reference to going into the tables, the primary keys, the foreign keys, and the composite keys, the when to many relationships and all those wonderful things that go there. And that will be used to develop an application which you are expected to do after you complete this course. So, this is the conceptual model over here. Now, one thing which you might be noting over here is the tags. Tags. So, what are the tags over here? Advertisement tags is a string of JavaScript, okay, it is a string of JavaScript, JavaScript used to define an ad placement on the website, which we have discussed in a lot of details before, and send requests to the demand partners to serve an ad on the web page, okay, serve on ad on the web page, this is the web page and the ad is going to be served on this web page. So, what are the important things over here? So, we have these advertisement tags in JavaScript, and these advertisement tags, they are tags and we have the advertisements also. And then we have online users, and user interests are of course there, so different users have different interests, and the online users advertisements, right, now let's look at the nitty-gritty details. So, first of all, let me define certain things just to recall to tell you that this over here is a one-to-many relationship, okay, and this relationship over here, this dotted corresponds to the, those foreign keys, okay, this is the foreign keys, right, and pk of course is the primary key, and fk of course is the foreign key, okay, and the pf over here is something, you might think new, this is the composite key, okay, this is the composite key, or this is the primary or the foreign key, this is the composite key, okay, now let's look at it, try to understand this, so we have this advertisement publishers over here, and they can have many advertisements, so we have this one-to-many advertisement, and this is the primary key which is the advertisement ID, okay, and then we have this primary key advertisement ID, and the tags over here in JavaScript, alright, and this is the primary key tag word, and this tag word, and this advertisement ID over here, they constitute the composite key, right, so we have online users, so online users may have different interests, okay, some may have the interests in sport, or some may have the interests in entertainment, and so on, right, so entertainment, and we have this YouTube also over here, similarly you have this, so combining the tags can be advertisement tags and user interests, and they're combined together over here, so we have this date and time details and other details also, so online users, other details are not important over here, so this is how the things are tied together, okay, and this is how this is the logical data model, which will be at the back end, and based using this data model, the online advertisement system will be developed, that's what I was looking at, okay, so this tag words could be chief flyers or shampoo depending upon the user interest, right, so I hope you understand all of this, and it is not very complicated, and this is the basis which will be used to develop this wonderful online advertisement system, so this is all I have for you in this module, thank you very much.