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1
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Okay, so let me see if
2
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anything changed after we did this last modification.
3
00:00:07,930 --> 00:00:09,530
Acutally, there is someting that I would like
4
00:00:09,530 --> 00:00:12,120
to do here. Because looking at this a little
5
00:00:12,120 --> 00:00:15,560
bit more, I noticed that there are two
6
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attributes, renewed and due date. That we have in
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loanable Item, right? But they don't seem to
8
00:00:21,640 --> 00:00:25,590
be really, attributes or characteristics of loanable Item.
9
00:00:25,590 --> 00:00:29,150
They're more of the characteristics of the association between the
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00:00:29,150 --> 00:00:31,450
Loanable Item and the patron. Wouldn't you agree?
11
00:00:32,470 --> 00:00:34,230
>> Well, yeah, it's not like you could
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only renew a book once in it's entire history.
13
00:00:37,644 --> 00:00:41,220
>> Right. Exactly, exactly. So, that's why what l like
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00:00:41,220 --> 00:00:43,970
to do is I would like to move those out of loanable
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item. And actually there is a construct that we can use
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to express this. It's called, we haven't seen it yet, but it's
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a special kind of class. It's called an association
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class. So, it's a class that is connected to
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a specific association. So what we can do
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here, we can create this class, which I'm going to
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call checked out. I'm going to, associate it with
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this, association. I'm going to connect it with this association. And
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then I'm going to move the due date and the
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renewed attributes From the LoanableItem here in this checked
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out class. So in this way, seems to me that
26
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it makes it very explicit for somebody looking at this
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00:01:20,910 --> 00:01:25,530
class diagram, that these characteristics are characteristics of the loan,
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and not of the elements involved in the loan.
29
00:01:28,200 --> 00:01:33,410
>> Can you do the same thing with Fine, isn't Fine a property of the
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loan? Yeah, actually is right because
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a fine is a fine for a specific loan, right?
32
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>> That's correct.
33
00:01:39,910 --> 00:01:41,950
>> Okay, so yeah. Then we can do that.
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We don't need to represent fine as a class, we can just transform
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that into an attribute that we can put into the checked out association class.
36
00:01:49,460 --> 00:01:50,560
>> Gotcha.
37
00:01:50,560 --> 00:01:52,760
>> Anything else?
38
00:01:52,760 --> 00:01:57,990
>> Yeah. It occurred to me that there's another thing that happens in one
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00:01:57,990 --> 00:02:00,260
of my scenarios, I put down
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00:02:00,260 --> 00:02:02,770
about the patron actually returning an item.
41
00:02:02,770 --> 00:02:07,620
>> Right. Okay, so we would probably need an additional operation,
42
00:02:07,620 --> 00:02:08,550
I guess, for the patron.
43
00:02:08,550 --> 00:02:08,990
>> Right.
44
00:02:08,990 --> 00:02:11,310
>> So, okay, so what I'm going to do, that's pretty easy
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00:02:11,310 --> 00:02:15,350
to do, I'm just going to add the return operation here in the
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patron, and when that happens, that will mean that I'll get rid
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00:02:19,310 --> 00:02:23,490
of this association class because the item is returned. Is that right?
48
00:02:23,490 --> 00:02:27,060
>> Well, what happens if somebody drops the
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00:02:27,060 --> 00:02:29,400
book in the book drop, but doesn't pay the,
50
00:02:29,400 --> 00:02:31,050
if it's overdue and doesn't pay the fine?
51
00:02:31,050 --> 00:02:32,700
Will that get rid of the information about what
52
00:02:32,700 --> 00:02:33,040
they owe?
53
00:02:33,040 --> 00:02:37,960
>> Oh, I see. So you can have the item being available, but you still
54
00:02:37,960 --> 00:02:42,510
want to know whether there is any pending fines on the book.
55
00:02:42,510 --> 00:02:44,390
>> Uh-huh, and how much those fines are.
56
00:02:44,390 --> 00:02:46,340
>> And how do you compute how much it is?
57
00:02:47,420 --> 00:02:52,710
>> It's how many days it was, from the time it was
58
00:02:52,710 --> 00:02:58,170
due, to when they returned it. I see. OK.
59
00:02:58,170 --> 00:03:00,380
So you know what we can do? I think
60
00:03:00,380 --> 00:03:03,690
we can put an additional attribute in the checked out
61
00:03:03,690 --> 00:03:07,190
class and I'm going to call it when returned and
62
00:03:07,190 --> 00:03:10,200
that item will have either a special value or it
63
00:03:10,200 --> 00:03:12,040
will contain the date in which the book was
64
00:03:12,040 --> 00:03:14,520
returned. So in this way you should be able to
65
00:03:14,520 --> 00:03:18,040
keep this in the system until it's paid, and also to compute
66
00:03:18,040 --> 00:03:19,970
how much the fine is. Is that working?
67
00:03:19,970 --> 00:03:23,210
>> So the special value is for a normal situation when they
68
00:03:23,210 --> 00:03:25,880
haven't, they don't owe anything and haven't returned it yet.
69
00:03:25,880 --> 00:03:28,080
>> Exactly so that will tell us that,
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00:03:28,080 --> 00:03:29,970
that the loan is still active basically.
71
00:03:29,970 --> 00:03:30,500
>> Great.
72
00:03:30,500 --> 00:03:31,480
>> Does that work for you?
73
00:03:31,480 --> 00:03:35,200
>> Yes. And you know, I like this. I mean, I feel pretty good
74
00:03:35,200 --> 00:03:38,490
about it. I think we have a nice class diagram. So what I'd like to
75
00:03:38,490 --> 00:03:43,280
do is just go off and clean it up a little bit, and put it
76
00:03:43,280 --> 00:03:48,640
in an IDE so I can pretty print it and rearrange things a little bit.
77
00:03:48,640 --> 00:03:50,080
And then I'd like to sit down again and
78
00:03:50,080 --> 00:03:52,730
just go through it for a last time. And
79
00:03:52,730 --> 00:03:54,900
for some final considerations. So if you don't mind
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00:03:54,900 --> 00:03:56,880
we will take a ten minute break and reconvene here.
81
00:03:56,880 --> 00:03:57,500
>> That's fine.
82
00:03:57,500 --> 00:03:57,990
>> Alright.
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