path: root/usth/ICT2.7/P3L2 A Tale of Analysis and Design Subtitles/4 - Adding Attributes - lang_en.srt

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Okay, so let me look at the requirements and

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it's something that I can see here that we didn't point out before is that

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there seems to be clearly some concept of a due date. And I'm telling you why

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I'm saying that because here, for example, I notice that it says when items are

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due. We mention overdue several times, so is

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this something we need to keep track of?

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>> Yeah remember when we used to stamp them on the books? In the stamp pad?

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>> Oh yeah yeah yeah! Oh course!

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>> Right? Yeah we definitely keep track of,

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the system has to keep track of when books are due.

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>> Okay. So it seems to me that one good way

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of doing that is by basically adding an attribute to the, item.

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>> Okay.

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>> And I'll just call it due date.

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>> Okay.

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>> So basically for each item in case it's loaned

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there will be this attribute that will contain the value of

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>> Okay.

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>> Of when, when the item is due. And then, something else that I noticed

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here is that down here, it seems like

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the requirements are saying that an item can

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be renewed only once. So, I guess, that's

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something we need to keep track of, right?

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>> Yeah.

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>> The system needs to know.

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>> We have to know whether they've renewed it or not.

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>> Okay so, I'll do a similar thing here. I think I want to go and add a an

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attribute that we'd call number of times renewed, and add it to the item class.

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>> Okay.

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>> And this is kind of more generic

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than what you need, because here it says only once, but

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let's say that in the future you want to allow it to,

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kind of renew twice, you'll be able to use these attributes again

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because, we can just count how many times it was renewed. Okay?

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>> Makes sense.

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>> Alright. And one last thing I want to point out.

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And this seems obvious but I'm going to check with

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you anyways. And seems like there is a basically the

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need to keep track of whether an item is checked

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out or not. If you look at the text here,

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the requirements here, I can see that check out and checked out are

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mentioned five times. So, I'm assuming that that's something also

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that we want to know about an item, whether it's checked out or not.

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>> We have to keep track of whether they're checked out.

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>> Okay, so I'll add an

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additional attribute there. So I'm going to again go

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back to the diagram and I'm

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just going to write here also the checked out attribute.

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And, I think that's it as far as I'm

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concerned. Is there anything that you think is missing?

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>> Well, I do have a question. Would checked out,

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better not be the case that someone can check out a reference book.

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>> Oh, I see, I see.

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>> Okay. I mean, it's only the books and

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the audio visual material that can be checked out.

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>> Right, right, right. Okay, so I, I guess, well the way I will fix that is,

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I'll probably put yet another attribute in the item class, and I'll

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call it loanable. And basically, this attribute is just telling us whether

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an item is loanable or not. So, when it's not true and

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loanable is not on. Basically, that item can be checked out.

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>> Okay. And, the system would know this.

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>> The system will know that.

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>> And prevent it from happening.

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>> And prevent it from happening. Okay?

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>> Alright.

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>> Perfect. So, we're going to do that and, any other objections,

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any other?

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>> No, that was my question.

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>> Okay, perfect, so what I'm going to do next, I

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mean, I haven't mentioned that yet, but you know classes right

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now we just looked at the attributes right that give

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you sort of the state of the class. And there's something

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else, there's a second part of the class that is kind of

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an orthogonal aspect, which is what the class can do. And we

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call those operations. So normally these kinds also have operations, I

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guess you know it would make sense to you as well.

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And one way, one very natural way to

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identify operations is to look at the requirements and

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look for verbs. Because verbs associated with an item

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will tell you basically what the item can do.

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>> Okay.

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>> So I, I'd like to go back to the requirements and

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start, the same way in which we underlined, nouns, we're going to underline

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verbs and we're going to see which ones of those verbs actually represent

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actions that we want to represent explicitly, we want to model explicitly in

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our class diagram.

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>> Okay.

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>> Okay.