path: root/usth/ICT2.7/P3L2 A Tale of Analysis and Design Subtitles/6 - Adding Relationships - lang_en.srt

1
00:00:00,420 --> 00:00:02,740
OK I like the way this class diagram is

2
00:00:02,740 --> 00:00:05,850
coming along. So at this point I think we

3
00:00:05,850 --> 00:00:08,300
have all the classes that we need. For each

4
00:00:08,300 --> 00:00:12,250
class we specified the attributes or the characteristics of the

5
00:00:12,250 --> 00:00:15,150
class. And we also specified the operations so we

6
00:00:15,150 --> 00:00:18,710
know what the class can do And, I like to

7
00:00:18,710 --> 00:00:22,110
kind of move forward on this, but I first

8
00:00:22,110 --> 00:00:25,690
want to see that you're fine with the class structure.

9
00:00:25,690 --> 00:00:27,500
So that's the way the class structure is going

10
00:00:27,500 --> 00:00:29,880
to be in terms of attributes and operations. So anything

11
00:00:29,880 --> 00:00:34,910
that bothers you? Well, one thing I didn't understand

12
00:00:34,910 --> 00:00:38,090
is how come you put check out over where

13
00:00:38,090 --> 00:00:40,350
the patron when it's really the item being checked

14
00:00:40,350 --> 00:00:46,280
out? Right. Okay. So that actually is you know, is a perfect

15
00:00:46,280 --> 00:00:48,030
segway for the next thing that really wanted

16
00:00:48,030 --> 00:00:50,780
to model. Because what you're talking about is basically a

17
00:00:50,780 --> 00:00:54,100
relationship between two classes which is something we haven't touched on

18
00:00:54,100 --> 00:00:57,582
yet. So we haven't, haven't looked at individual classes. But now, it

19
00:00:57,582 --> 00:01:00,720
is typical, now we are looking more at requirements, we're starting to

20
00:01:00,720 --> 00:01:04,800
find more things about our system, and what you're pointed out right

21
00:01:04,800 --> 00:01:08,370
now is the fact that patron and item are somehow related. So

22
00:01:08,370 --> 00:01:11,020
this checkout operation is not really something that belongs only on in

23
00:01:11,020 --> 00:01:13,660
the patron, because it needs to know about the item. And it

24
00:01:13,660 --> 00:01:15,790
doesn't belong only on the item because it needs to know about

25
00:01:15,790 --> 00:01:19,640
the patron. So, it's something that associates the patron and

26
00:01:19,640 --> 00:01:22,600
the item. Okay. And that's exactly the way we call

27
00:01:22,600 --> 00:01:24,630
in the UML which is the notation that we're using

28
00:01:24,630 --> 00:01:29,060
here this kind of relationship. So, we're going to represent that

29
00:01:29,060 --> 00:01:32,820
by drawing a line between these two classes that tells

30
00:01:32,820 --> 00:01:35,220
us there is an association. And we're also going to

31
00:01:35,220 --> 00:01:37,890
give a name to this. Since this refers to the

32
00:01:37,890 --> 00:01:40,280
fact of checking out items. We're just going to call

33
00:01:40,280 --> 00:01:43,794
it, checkout. Gotcha. And notice that this basically you

34
00:01:43,794 --> 00:01:48,500
know,eventually will end up kind of replacing this attribute. Because

35
00:01:48,500 --> 00:01:51,780
the existence of this association will tell us that

36
00:01:51,780 --> 00:01:53,932
this is checked out. We're, we're not going to, you know,

37
00:01:53,932 --> 00:01:55,428
do it right now, but in the final cleanup

38
00:01:55,428 --> 00:01:58,750
or the diagram, this name will disappear. Okay. Okay.

39
00:01:58,750 --> 00:02:02,190
And so since we started talking about relationships and

40
00:02:02,190 --> 00:02:05,280
associations, is there any other kind of relationship that you

41
00:02:05,280 --> 00:02:08,805
see here? Well, what you just did with checked

42
00:02:08,805 --> 00:02:12,009
out is, it seems similar to the whole issue

43
00:02:12,009 --> 00:02:16,090
of requests. It is, it is. So a request

44
00:02:16,090 --> 00:02:19,580
is something else that happens in both, you know, in

45
00:02:19,580 --> 00:02:22,090
the patron and in the item, it involves both.

46
00:02:22,090 --> 00:02:24,070
And in fact in a request, I would definitely

47
00:02:24,070 --> 00:02:26,950
represent this as an additional association. So I will

48
00:02:26,950 --> 00:02:30,730
just draw an another line between these two that represent

49
00:02:30,730 --> 00:02:33,804
that specific kind of relationship and I will call it

50
00:02:33,804 --> 00:02:37,330
request. So that indicates that this association refers to a

51
00:02:37,330 --> 00:02:41,660
request that also connects the patron with an item. Okay.

52
00:02:41,660 --> 00:02:45,710
And, let's see. Any, anything else that jumps at you?

53
00:02:45,710 --> 00:02:47,590
Yeah, well, how about all these ones down at the

54
00:02:47,590 --> 00:02:50,080
bottom? I mean book and item's got to be

55
00:02:50,080 --> 00:02:52,920
related, right? A book is a kind of item, And

56
00:02:52,920 --> 00:02:55,860
audiovisual... are there associations between them? Can you repeat

57
00:02:55,860 --> 00:02:58,790
that, you said that the book, yeah? Is

58
00:02:58,790 --> 00:03:02,550
a kind of item. Perfect, that's exactly what we're

59
00:03:02,550 --> 00:03:04,700
modeling next, which is, this, what we call the

60
00:03:04,700 --> 00:03:07,900
is-a relationship. So you said, a book is an item?

61
00:03:07,900 --> 00:03:13,346
A book is an item. And, we can model that in the diagram. So, we do that

62
00:03:13,346 --> 00:03:17,409
using another kind of relationship between the classes. So

63
00:03:17,409 --> 00:03:21,210
we're going to represent that as a specialization we call it.

64
00:03:21,210 --> 00:03:24,890
And, a specialization is indicated in this way. Okay?

65
00:03:24,890 --> 00:03:27,410
With this arrow at the end, so a solid

66
00:03:27,410 --> 00:03:30,800
with this kind of arrow at the end. And

67
00:03:30,800 --> 00:03:34,160
we can do the same for book, magazine, reference book

68
00:03:34,160 --> 00:03:36,200
and audiovisual material. So we're all going to connect,

69
00:03:36,200 --> 00:03:37,950
we're going to connect all of them, to the

70
00:03:37,950 --> 00:03:43,190
item, using the same kind of connection. And now

71
00:03:43,190 --> 00:03:47,200
that we have connected all these four, with item

72
00:03:47,200 --> 00:03:50,620
and indicated them in subclasses. That's something else that we can

73
00:03:50,620 --> 00:03:54,370
do. So we can make this kind of cleaner. And I'll

74
00:03:54,370 --> 00:03:56,360
tell you what I mean by that. So now we have

75
00:03:56,360 --> 00:04:00,190
this loanable attribute that refers to item, but it seems to

76
00:04:00,190 --> 00:04:03,100
me from what you were saying before, that loanable is not

77
00:04:03,100 --> 00:04:05,490
really an attribute of an item. Right? It's more of a

78
00:04:05,490 --> 00:04:09,240
characteristic of the type of item. Right. Is that right? Right.

79
00:04:09,240 --> 00:04:13,120
Books, and audio/visual are loanable but the others aren't.

80
00:04:13,120 --> 00:04:16,450
Okay, and so representing it here, it's okay to,

81
00:04:16,450 --> 00:04:20,579
it will work. But it's not really right so from

82
00:04:20,579 --> 00:04:23,590
the style standpoint it doesn't really you know,

83
00:04:23,590 --> 00:04:26,100
it's not the best way of modeling this. What we're going to

84
00:04:26,100 --> 00:04:30,130
do instead, we're going to use this specialization relationship to make

85
00:04:30,130 --> 00:04:33,000
that more explicit. To make it cleaner. Okay, so what

86
00:04:33,000 --> 00:04:35,300
I'm doing here is I'm going to take this hierarchy

87
00:04:35,300 --> 00:04:38,130
of classes, this is just on two levels now, and I'm

88
00:04:38,130 --> 00:04:40,380
going to kind of make it a little richer.

89
00:04:40,380 --> 00:04:43,470
So I'm going to add an intermediate set of

90
00:04:43,470 --> 00:04:45,756
classes. And in particular I'm going to have these two

91
00:04:45,756 --> 00:04:48,306
classes that I'm going to call non loanable item and loanable

92
00:04:48,306 --> 00:04:51,790
item. So, they're both items but they tell me

93
00:04:51,790 --> 00:04:55,490
clearly that some items are loanable and some items

94
00:04:55,490 --> 00:04:59,392
are not. Okay. Okay. And then I'm simply going to

95
00:04:59,392 --> 00:05:03,192
put book and audio video material as subclasses of loanable

96
00:05:03,192 --> 00:05:07,980
item and reference book and magazine as subclasses of non-loanable

97
00:05:07,980 --> 00:05:10,510
item. So, if we look at this diagram now it's

98
00:05:10,510 --> 00:05:13,650
pretty clear what is loanable and what is not. And

99
00:05:13,650 --> 00:05:16,070
it's actually is a very clean, much cleaner

100
00:05:16,070 --> 00:05:18,980
design. And, and I see you've, gotten rid of

101
00:05:18,980 --> 00:05:21,560
the loanable attribute, too. I did. Because at

102
00:05:21,560 --> 00:05:24,130
this point this is already represented by the fact of

103
00:05:24,130 --> 00:05:28,570
having these two classes. And actually, something else that I did

104
00:05:28,570 --> 00:05:31,820
is that I moved all these attributes, value,

105
00:05:31,820 --> 00:05:34,220
due date, renewed and checked out, that makes

106
00:05:34,220 --> 00:05:37,452
sense only for loanable item. From item to

107
00:05:37,452 --> 00:05:40,450
loanable item. So at this point, this really

108
00:05:40,450 --> 00:05:42,600
is telling me that, you know, these

109
00:05:42,600 --> 00:05:46,410
characteristics are just meaningful for the loanable item,

110
00:05:46,410 --> 00:05:53,800
and not for the other ones. Well, speaking of that, the way that you got the

111
00:05:53,800 --> 00:05:57,270
lines going in the diagram here is you still have

112
00:05:57,270 --> 00:05:59,920
request and checked out going to item, even though you

113
00:05:59,920 --> 00:06:02,610
can't request non loanable Items. You can't check out non

114
00:06:02,610 --> 00:06:05,630
loanable Items. Oh, you were right actually. You got me on

115
00:06:05,630 --> 00:06:10,940
that one. You're exactly right. So this associations are between

116
00:06:10,940 --> 00:06:13,440
the two wrong classes. So, I guess, at this point,

117
00:06:13,440 --> 00:06:16,450
you can probably go and fix the diagram yourself. Well,

118
00:06:16,450 --> 00:06:19,120
can we just make the lines go from patron to loanable

119
00:06:19,120 --> 00:06:21,640
item instead of to item? That's exactly the way in which we

120
00:06:21,640 --> 00:06:25,550
are going to fix it. So, we're going to move these two associations down

121
00:06:25,550 --> 00:06:29,190
here. And at this point, this will represent the right relationships in

122
00:06:29,190 --> 00:06:31,850
the, in the diagram, and in the system. Makes sense to me.