Chris! I told you not to do that. That is going to complicate everything. It is very hard to have the same key to two different cells. DARRELL: Come off it, Neil. Forget that for a minute. JACK: What is complicated? We all know what "A and C" and "B and D" is. It is just a matter of looking up a name in one of our two different files. We don't do that much anymore. We just don't because there is so much information in each one of these files. Just a minute, Neil, because you are wrong. I never did say that. What I did say was that we should have a file for each key and when we run out of a file, and if you decide you want to change your key, all you need to do is copy the key from one file to another. That is fine, and we already do that. NEIL: When I said, "I am wrong," I was talking about your attitude about using the same key. JACK: Wait, Neil. Let us work through this. Why is this going to be hard to have the same key to two different cells? It is not hard to have the same key to two different cells. In fact, we have already done it. We have at least two different cells using the same key. NEIL: We are not talking about two different cells. We are talking about two different data items, and there is no reason why we have to have two different files and two different keys for two different data items. I was in favor of having two different data items, and having two different files, and then the problem is that you are putting them into one file and making them one item. JACK: Neil, wait a second. That is not a problem. What we are going to do now is take your example and change it to match what we are doing. NEIL: Oh, good, I love it when Neil does that. He changes an example to match his behavior. I love it. DARRELL: Neil, I love it when Darrell does that, too. He changes an example to match what we were doing. NEIL: All right, then I know that this is one of the things that Neil has that I do not have. DARRELL: But you should have it because we do it all the time. NEIL: I do not have it. Neil likes to change examples to match what we were doing. JACK: No, Neil is talking about two different keys. I agree with Darrell. I would want to keep it together in one file. NEIL: No, it is the same thing. What I am saying is that you are going to be looking at the primary key, not the primary key, and you are going to be looking at both the name and the time stamp and both of them are unique. I just don't want you to think that this difference in primary keys between this and that is a big deal. That is all. JACK: Is that why you said "if you want to get into two files?" NEIL: Well, because there is no difference between the data in the second file and the second file. They are the same data. JACK: With two different keys. NEIL: No. You can have these files, and if you want to keep them separate, that is fine, too. JACK: All right, we know this works. We just talked about this. We have got two files, A and B. We used a primary key, and we have got a time stamp. We have an index on each one of these files, and we can look up the data in these files. NEIL: And because we have got the time stamp, we have got the difference in data with the time stamp, and we have got the difference in data using the key. JACK: That is true, and we talked about it in the presentation. NEIL: Well, it is interesting that now, all of a sudden, when we are going to try to use it for the first time, it does not work because you have to keep the same key and all that sort of thing. DARRELL: Neil, we have got to come up with some solutions to problems. Maybe you can help us. JACK: What is this about "the key." NEIL: Do you see where this is going? Do you think it is easier to deal with the key when we actually know about the time stamp? JACK: No, that is not the point. The point is we should be able to use the same key for both of the records and we have time stamp and we have an index and we can look up the data. That is all. NEIL: The reason I want a different key, is I want to associate the same key to different cells, and I want to be able to update a key. That is what I want. JACK: What do you mean update a key? I update the key when I find the cell. NEIL: But you don't know which cell it is. JACK: That is the point. You just keep track of the data, don't you? NEIL: If I understand your explanation, if I want to look up data in file A, I am going to look up it with the primary key, and if I want to look it up in file B, I am going to look it up with the primary key. JACK: What is wrong with that? NEIL: The problem with that is I don't want the same key to be used to different data items. JACK: Yes, you do. NEIL: Then why don't you have a time stamp in each file. JACK: So you want to break the primary key. NEIL: If I can't, then I have to have two different keys, don't I? JACK: No, we have got that down. Each file uses the same key. You have to make sure that your keys are the same. NEIL: There are two keys. The problem is that I have got two data items. I have a choice. I can either use one key, or I have to use two keys. JACK: You can't, because you cannot associate the same key to two different data items. NEIL: Then you have got to do something about it. DARRELL: Neil, I think that we are all with you on this one. The idea is a real good idea. It is a neat idea. The data set is real big, especially for today's standards. NEIL: I am not complaining about the file. I am complaining about the unique key. You have got a data set, and you got to give it a unique key, and you use the same unique key for both files, or you use two unique keys. JACK: One of the big problems with this is that you can't have a primary key that changes. NEIL: What do you mean? You can. JACK: Let us say this was an application. Let us say that this was an application that did financial information for a company. Let us say that there was a primary key. I mean, what you are saying is you can have two different data items, and you are going to use the same primary key for both of them. What happens if you have the same name for a primary key? Then you cannot distinguish between the two data items. NEIL: Then you change the key. JACK: Then you do have the problem of the primary key. DARRELL: Could we agree that the most important issue is the key? Because the data, as it is, we understand it and we don't really have a problem. The problem is going to come when you are trying to make the update of the data be automatic. Then the key is going to be important. JACK: So we get two files and two primary keys, and the only thing we will have to worry about is that you don't use the same primary key twice. That is all. DARRELL: No, when you are designing the application, you get into the problem when we are doing the update. JACK: Dang, you caught me. I am not doing that problem now. It is solved. NEIL: It is solved. You are not doing it now, but the time will come where you will have to do it, and