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Okay, so let me look at the requirements and

2
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it's something that I can see here that we didn't point out before is that

3
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there seems to be clearly some concept of a due date. And I'm telling you why

4
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I'm saying that because here, for example, I notice that it says when items are

5
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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.

13
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>> Okay.

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

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>> Okay.

16
00:00:42,400 --> 00:00:45,360
>> 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

18
00:00:48,315 --> 00:00:48,520
>> Okay.

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00:00:48,520 --> 00:00:55,710
>> Of when, when the item is due. And then, something else that I noticed

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00:00:55,710 --> 00:00:58,734
here is that down here, it seems like

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00:00:58,734 --> 00:01:00,900
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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00:01:04,190 --> 00:01:05,933
something we need to keep track of, right?

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00:01:05,933 --> 00:01:06,056
>> Yeah.

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>> The system needs to know.

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00:01:06,700 --> 00:01:08,360
>> We have to know whether they've renewed it or not.

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00:01:08,360 --> 00:01:14,132
>> 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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00:01:28,690 --> 00:01:31,090
because, we can just count how many times it was renewed. Okay?

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>> Makes sense.

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00:01:31,680 --> 00:01:35,980
>> 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

38
00:01:38,310 --> 00:01:43,150
you anyways. And seems like there is a basically the

39
00:01:43,150 --> 00:01:46,090
need to keep track of whether an item is checked

40
00:01:46,090 --> 00:01:48,210
out or not. If you look at the text here,

41
00:01:48,210 --> 00:01:51,080
the requirements here, I can see that check out and checked out are

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00:01:51,080 --> 00:01:55,070
mentioned five times. So, I'm assuming that that's something also

43
00:01:55,070 --> 00:01:58,080
that we want to know about an item, whether it's checked out or not.

44
00:01:58,080 --> 00:01:59,970
>> We have to keep track of whether they're checked out.

45
00:01:59,970 --> 00:02:01,930
>> Okay, so I'll add an

46
00:02:01,930 --> 00:02:04,340
additional attribute there. So I'm going to again go

47
00:02:04,340 --> 00:02:06,480
back to the diagram and I'm

48
00:02:06,480 --> 00:02:10,139
just going to write here also the checked out attribute.

49
00:02:12,260 --> 00:02:14,590
And, I think that's it as far as I'm

50
00:02:14,590 --> 00:02:16,330
concerned. Is there anything that you think is missing?

51
00:02:16,330 --> 00:02:21,077
>> Well, I do have a question. Would checked out,

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00:02:21,077 --> 00:02:27,140
better not be the case that someone can check out a reference book.

53
00:02:27,140 --> 00:02:28,400
>> Oh, I see, I see.

54
00:02:28,400 --> 00:02:30,120
>> Okay. I mean, it's only the books and

55
00:02:30,120 --> 00:02:31,780
the audio visual material that can be checked out.

56
00:02:31,780 --> 00:02:37,790
>> Right, right, right. Okay, so I, I guess, well the way I will fix that is,

57
00:02:37,790 --> 00:02:42,300
I'll probably put yet another attribute in the item class, and I'll

58
00:02:42,300 --> 00:02:45,860
call it loanable. And basically, this attribute is just telling us whether

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00:02:45,860 --> 00:02:49,580
an item is loanable or not. So, when it's not true and

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00:02:49,580 --> 00:02:53,480
loanable is not on. Basically, that item can be checked out.

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00:02:53,480 --> 00:02:55,174
>> Okay. And, the system would know this.

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00:02:55,174 --> 00:02:56,450
>> The system will know that.

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00:02:56,450 --> 00:02:57,160
>> And prevent it from happening.

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00:02:57,160 --> 00:02:58,240
>> And prevent it from happening. Okay?

65
00:02:58,240 --> 00:02:58,750
>> Alright.

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00:02:58,750 --> 00:03:02,918
>> Perfect. So, we're going to do that and, any other objections,

67
00:03:02,918 --> 00:03:04,035
any other?

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00:03:04,035 --> 00:03:05,730
>> No, that was my question.

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00:03:05,730 --> 00:03:08,040
>> Okay, perfect, so what I'm going to do next, I

70
00:03:08,040 --> 00:03:11,130
mean, I haven't mentioned that yet, but you know classes right

71
00:03:11,130 --> 00:03:12,890
now we just looked at the attributes right that give

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00:03:12,890 --> 00:03:16,140
you sort of the state of the class. And there's something

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00:03:16,140 --> 00:03:19,185
else, there's a second part of the class that is kind of

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00:03:19,185 --> 00:03:22,520
an orthogonal aspect, which is what the class can do. And we

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00:03:22,520 --> 00:03:25,640
call those operations. So normally these kinds also have operations, I

76
00:03:25,640 --> 00:03:28,000
guess you know it would make sense to you as well.

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00:03:28,000 --> 00:03:30,070
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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00:03:33,310 --> 00:03:36,850
look for verbs. Because verbs associated with an item

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00:03:36,850 --> 00:03:38,480
will tell you basically what the item can do.

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00:03:38,480 --> 00:03:38,900
>> Okay.

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00:03:38,900 --> 00:03:41,250
>> So I, I'd like to go back to the requirements and

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00:03:41,250 --> 00:03:45,110
start, the same way in which we underlined, nouns, we're going to underline

84
00:03:45,110 --> 00:03:49,340
verbs and we're going to see which ones of those verbs actually represent

85
00:03:49,340 --> 00:03:53,120
actions that we want to represent explicitly, we want to model explicitly in

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00:03:53,120 --> 00:03:53,950
our class diagram.

87
00:03:53,950 --> 00:03:54,490
>> Okay.

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00:03:54,490 --> 00:03:54,750
>> Okay.