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Once we collected the required knowledge on the requirements for

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the system that we're developing, we need to model it in

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a structured and clear way, so that it can be

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analyzed and refined. And there are really tons of ways to

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do that, depending on your focus and objectives. More specifically,

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when modeling requirements you need to decide what you want to

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model and how you want to model it. So let's look

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at these two aspects independently. What you decide to model depends

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on where your emphasis is. That is on which

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aspects of the requirements you want to focus. For

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example if your emphasis is on the characteristics of

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the enterprise of the company that you are analyzing you

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may want to model goals and objectives of the

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company, or its organizational structure, its task and dependencies

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and so on. Conversely, if your focus is on

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information and behaviors, you might want to concentrate on aspects

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such as the structure of information, various behavioral views

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some of which we will see in the next

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lesson, or maybe time or sequencing requirements. Finally, if

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you're mostly interested in the quality aspects of your

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system, you will focus on the various non-functional properties

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of the software that are relevant in the context

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considered. For example reliability, robustness, security, and so on.

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You will just pick the ones that are relevant for

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your context. And as we said, there's a second dimension.

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After you have decided what to model in your system,

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you have to decide how you want to model it.

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So I want to show here some options for modeling

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enterprises, information, and quality aspects. And as you can see

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here for each type of information there are many possible

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models that we can use to represent it. And all

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these models have advantages and

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disadvantages, different levels of formality and

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different focus. Something else that I want to point out

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about these models is the fact that these models are often

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orthogonal to one another, especially if we consider models in different

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categories. So what that means is that they're complimentary rather than

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mutually exclusive. Different models can be used to provide views

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of the requirements from different perspectives, and we will not see

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most of these models in this course, but I wanted to

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list them anyways to give you an idea of how many

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there are and how vast is this area. As far

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as we are concerned in the course and for the

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projects we will express requirements using one of two main

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ways. Using natural language, that is informal specifications and using

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UML diagrams, which is graphical models. And we will introduce

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UML and the most important diagrams in the next lesson.

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And the only other type of models that I want

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to mentions explicitly are goal models because they're extremely popular.

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So the main idea with goal models is it start with the main goal of

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the system and then keep refining it

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by decomposing it in sub-goals. So it's kind

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of a very natural way of progressing.

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And you continue this refinement until you get

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to goals that can be operationalized, and represent

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the basic units of functionality of the system.