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1
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So how do we represent a class in a class
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diagram? Class is represented as a rectangle with three parts. The
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first part is the class name. Classes should be named using
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the vocabulary of the domain, so we should pick names that
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make sense. And the normal naming standard requires that the classes
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are singular nouns starting with a capital letter. The second part
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of the class are the attributes of the class, where the
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set of attribute for the class, we find the state for
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the class. And, we can list an attribute simply by
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name, or we can provide the additional information. For example,
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we might define the title of the attribute, and we
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might also define the initial. Value for the attribute. Finally, the
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third part of the class consist of the operations of
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the class. And normally, the operations of the class are represented
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by name, with a list of arguments. That the operation
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will take as input, and with a result type. So the
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type of the result produced by the operation. Something
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else you can notice in this representation is the
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fact that there is a minus before these attributes
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and a plus before this operation. This indicates what is
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called the visibility of these class members. So the
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minus indicates that the attributes are private to the class.
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So only instances of this class, roughly speaking, can
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access these attributes. And notice that this is what allows
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to enforce the information hiding principle, because clients of
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the class cannot see what's inside this box, what are
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these attributes. The plus conversely indicates that this is a
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public operation. So something that is visible outside the class.
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And, in fact, normally, this is what we use to
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define the interface for my class. So we encapsulate the
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state of the class and we make it accessible to
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the extent that we want and that is needed through
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a set of public operations. Last thing I want to
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note is the use of these ellipses that we can
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utilize if we want to indicate that there are more
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attributes for example, or more operations. But we just don't
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want to list them now. Okay now that we know what
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a class is, and how it is represented, let's start
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our analysis of our course management system. By identifying the
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relevant classes in the system, we need to bring back the
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description of our system. And what we want to
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do, is that we want to go through the description
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and underline the relevant nouns in the description. And here
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I encourage you to stop the video and to do
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the exercise of underlying such nouns yourself before listening to
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my explanation into how I do it. For example in
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this case I might want to underlined the registration manager which
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is a noun and probably a relevant one. The scheduling
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algorithm, also seems like a relevant concept, so
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is the course. The course offerings, again, course offerings
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over here. Definitely, the students seem to be a
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relevant noun and so is probably the registration form
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and the professors. Okay, so, at this point, I
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identified seven possible classes for my system. So, what
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I'm going to do is simply to create classes for
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each one of these nouns. So my initial class
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diagram looks exactly like this, with the seven classes where
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for each class, I picked the name that is representative of
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the domain. So, in this case, it's pretty straightforward. The
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registration form is called registration form, the student is called student
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and so on and so forth. But you can already
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see how this analysis method is starting from a description of
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the real world and it's just identifying objects or classes
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in the real world and transforming them into entities in my
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analysis document.
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