Subtitles of the Movie

This movie introduces you to two of the most common kinds of UML diagrams, use case diagrams and class diagrams. Use case diagrams such as the one that you see on your screen model the system's functionality from a perspective outside the system. As such these diagrams identify the primary elements and processes that make up the system. In a use case diagram actors represented by stick figures like the one you see here, interact with the system in order to accomplish some goal and each goal is a use case. So a use case is a goal, often a user level goal that some actor has in interacting with the system. Actors which may be people or other systems are best understood in terms of roles. So for example the role this actor plays could be customer for example, could be employee and so on. Not an individual but a role that a person might play or another system might play. And what a use case diagrams shows is a high level view of the different goals, the different use cases that various actors have in regard to the system. The use case diagram also shows which actors, there certainly can be more then one are associated with which use cases. And as you can also see from within the diagram a use case diagram will show you relationships between individual use cases. For example we have three kinds of relationships between use cases in this diagram. We have the include dependency, this use case must include this use case in order to be complete. We have the extend dependency, this use case may optionally include or extend this use case before it completes. And we have a generalized relationship in which these two child use cases generalize to the parent or inherit various traits from the parent. So use cases show actors and goals and also the various associations among actors and among the goals themselves. Use cases often originate in the business requirement specification later on they're useful for developing test cases. Here's an example of a class diagram, class diagrams are often used to refine use case diagrams, many modelers consider class diagrams the backbone of their overall model of a system. A class diagram describes the kinds of objects that populate the system as well as the kinds of static relationships that exist among those classes and objects. Classes have features as you can see in this box right here for class one and feature describes the attributes and operations of a class. Attributes are the properties of a class and operations are the methods or the functionalities of the class. There are various kinds of associations among classes. You can show simple association, you can again show generalization with a parent child relationship. You can show aggregation and composition as you can see here you can show multiplicity and class diagrams can get pretty complex. This is a very simple diagram and they can show a lot more. They can show interfaces, they can show templates and various other kinds of stereotypes, various ways of extending the concept of class in a more specialized way. Because class diagrams are so important and because they can show so much this course has two sets of movies on class diagrams. There's one set on the basics and there's another set on advanced class diagrams. So there's plenty to learn about class diagrams.