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+1
+00:00:00,240 --> 00:00:02,880
+Okay, so let me look at the requirements and
+
+2
+00:00:05,500 --> 00:00:09,150
+it's something that I can see here that we didn't point out before is that
+
+3
+00:00:09,150 --> 00:00:13,540
+there seems to be clearly some concept of a due date. And I'm telling you why
+
+4
+00:00:13,540 --> 00:00:17,610
+I'm saying that because here, for example, I notice that it says when items are
+
+5
+00:00:17,610 --> 00:00:22,580
+due. We mention overdue several times, so is
+
+6
+00:00:22,580 --> 00:00:24,410
+this something we need to keep track of?
+
+7
+00:00:24,410 --> 00:00:27,510
+>> Yeah remember when we used to stamp them on the books? In the stamp pad?
+
+8
+00:00:27,510 --> 00:00:28,240
+>> Oh yeah yeah yeah! Oh course!
+
+9
+00:00:28,240 --> 00:00:30,600
+>> Right? Yeah we definitely keep track of,
+
+10
+00:00:30,600 --> 00:00:32,390
+the system has to keep track of when books are due.
+
+11
+00:00:32,390 --> 00:00:35,300
+>> Okay. So it seems to me that one good way
+
+12
+00:00:35,300 --> 00:00:39,660
+of doing that is by basically adding an attribute to the, item.
+
+13
+00:00:39,660 --> 00:00:40,590
+>> Okay.
+
+14
+00:00:40,590 --> 00:00:41,910
+>> And I'll just call it due date.
+
+15
+00:00:41,910 --> 00:00:42,400
+>> Okay.
+
+16
+00:00:42,400 --> 00:00:45,360
+>> So basically for each item in case it's loaned
+
+17
+00:00:45,360 --> 00:00:48,315
+there will be this attribute that will contain the value of
+
+18
+00:00:48,315 --> 00:00:48,520
+>> Okay.
+
+19
+00:00:48,520 --> 00:00:55,710
+>> Of when, when the item is due. And then, something else that I noticed
+
+20
+00:00:55,710 --> 00:00:58,734
+here is that down here, it seems like
+
+21
+00:00:58,734 --> 00:01:00,900
+the requirements are saying that an item can
+
+22
+00:01:00,900 --> 00:01:04,190
+be renewed only once. So, I guess, that's
+
+23
+00:01:04,190 --> 00:01:05,933
+something we need to keep track of, right?
+
+24
+00:01:05,933 --> 00:01:06,056
+>> Yeah.
+
+25
+00:01:06,056 --> 00:01:06,700
+>> The system needs to know.
+
+26
+00:01:06,700 --> 00:01:08,360
+>> We have to know whether they've renewed it or not.
+
+27
+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
+
+28
+00:01:14,132 --> 00:01:19,140
+attribute that we'd call number of times renewed, and add it to the item class.
+
+29
+00:01:19,140 --> 00:01:19,760
+>> Okay.
+
+30
+00:01:19,760 --> 00:01:21,140
+>> And this is kind of more generic
+
+31
+00:01:21,140 --> 00:01:23,180
+than what you need, because here it says only once, but
+
+32
+00:01:23,180 --> 00:01:25,800
+let's say that in the future you want to allow it to,
+
+33
+00:01:25,800 --> 00:01:28,690
+kind of renew twice, you'll be able to use these attributes again
+
+34
+00:01:28,690 --> 00:01:31,090
+because, we can just count how many times it was renewed. Okay?
+
+35
+00:01:31,090 --> 00:01:31,680
+>> Makes sense.
+
+36
+00:01:31,680 --> 00:01:35,980
+>> Alright. And one last thing I want to point out.
+
+37
+00:01:35,980 --> 00:01:38,310
+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
+
+42
+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,
+
+52
+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
+
+59
+00:02:45,860 --> 00:02:49,580
+an item is loanable or not. So, when it's not true and
+
+60
+00:02:49,580 --> 00:02:53,480
+loanable is not on. Basically, that item can be checked out.
+
+61
+00:02:53,480 --> 00:02:55,174
+>> Okay. And, the system would know this.
+
+62
+00:02:55,174 --> 00:02:56,450
+>> The system will know that.
+
+63
+00:02:56,450 --> 00:02:57,160
+>> And prevent it from happening.
+
+64
+00:02:57,160 --> 00:02:58,240
+>> And prevent it from happening. Okay?
+
+65
+00:02:58,240 --> 00:02:58,750
+>> Alright.
+
+66
+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?
+
+68
+00:03:04,035 --> 00:03:05,730
+>> No, that was my question.
+
+69
+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
+
+72
+00:03:12,890 --> 00:03:16,140
+you sort of the state of the class. And there's something
+
+73
+00:03:16,140 --> 00:03:19,185
+else, there's a second part of the class that is kind of
+
+74
+00:03:19,185 --> 00:03:22,520
+an orthogonal aspect, which is what the class can do. And we
+
+75
+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.
+
+77
+00:03:28,000 --> 00:03:30,070
+And one way, one very natural way to
+
+78
+00:03:30,070 --> 00:03:33,310
+identify operations is to look at the requirements and
+
+79
+00:03:33,310 --> 00:03:36,850
+look for verbs. Because verbs associated with an item
+
+80
+00:03:36,850 --> 00:03:38,480
+will tell you basically what the item can do.
+
+81
+00:03:38,480 --> 00:03:38,900
+>> Okay.
+
+82
+00:03:38,900 --> 00:03:41,250
+>> So I, I'd like to go back to the requirements and
+
+83
+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
+
+86
+00:03:53,120 --> 00:03:53,950
+our class diagram.
+
+87
+00:03:53,950 --> 00:03:54,490
+>> Okay.
+
+88
+00:03:54,490 --> 00:03:54,750
+>> Okay.
+