 So students, in this module, we will look at the nuts and bolts, the nitty-gritty details about an airline reservation system. We will look at the logical model and we will look at the data model also. Of course, the logical model, as I said before, is at a higher level of abstraction. It is for the decision makers and the managers and the data model is the stuff which is used by the architects, by the system designers, okay, by the people like you, all right. So airline reservation systems are very complex systems and it is a complex piece of software which is running over the network and they are expensive to create, they are expensive to maintain and there are a lot of details which are taken into considerations in an airline reservation system, okay. I have given you some of the background about the airline reservation in the previous module. Now we will look at the functional details, the logical details with reference to the data. So we will be looking at the conceptual data model and we will be looking at the logical data model, conceptual and the logical data model. So now let's look at more details and I will also give a very brief explanation of a definition which is central to this kind of a system and that I also mentioned in the background, right, but I will also talk about you, talk with you about it. So this is the conceptual data model as you can see on the screen and something which is over here is legs, legs over here also. So what is a leg? It is the flight that maintains the same flight number and aircraft throughout its journey from one airport to another airport. So we have this airport A1, we have this airport A2, we have this airport A3 and it goes from here and goes from here and they have this same leg, okay. This is the flight number, right. Now let's look at in more detail. So there are many, many airports in the world. So an airport has these legs and the airports have this flight schedules also and associated with the flight schedules are the flight cost and if you recall in the previous module I discussed in a lot of details how this costing is done. It depends upon how in advance the reservation was made and what is the duration of the stay and what is the class of the passenger and so on, okay. So we have these all those details and then we have these passengers and itinerary reservations if you recall itinerary is a seat, okay. So these are the seats over here and then are the payments, payments reservation payments itinerary reservation seat payments and all of those things. So this is the conceptual data model and now we will look at the more interesting which is the logical model. Now let's look at it in more details. This dotted over here is the referential integrity constraint, okay. It is the referential integrity constraint which everybody knows I hope from this previous courses and if you read and you see over here where we have this over here PF. This PF is the composite key, okay. This is the composite key. This is the itinerary of the reservations and a passenger can have many reservations and if you recall from the previous module these booking agents they are also making the reservations and they are also making many reservations, okay. Everyone is making those reservations, right and those reservations of course involve payment dollars, okay money, right. So this is the composite key where we are tying these things together itinerary reservations and the payments go into the reservation payments table. So now we have these itinerary legs, okay. So this leg is flight number which is actually the leg number, okay. Flight number and of course this is the foreign key and we have the origin airport and the destination airport if you recall the leg is going from say airport A1 to airport A2 to airport A3. This is a leg if you recall, okay this is the leg and then we have this flight schedules. So these airports and airport can have many flight schedules and of course this is the departure date and the arrival date also and then are the flight costs, okay. Valid to the date flight cost. These things to be understood aircraft type and code this also includes and covers the cost also and there is the reference of the calendar, okay. Day number and the business day and the year so their number of ways of keeping track of the time. This is all how the things are falling together. So this is what goes behind this is the logical model of the airline reservation system, okay. This is we are talking about the online airline reservation system. This is the logical model behind that system and if you some part of your carrier you are there and you would like to or you are required to develop an online airline reservation system. This is the logical data model. I have given you the background and I have also discussed with you the conceptual data model also. So logical data model, conceptual data model together you will be able to design and then subsequently develop that system which will be an online system with the front end and the back end with all the details with all the tools that have been explained to you. You have been exposed to all of those things so everything should tie it together. That is all I have for you in this module thank you very much.