Đây là mối quan hệ duy nhất tồn tại giữa một diễn viên và trường hợp sử dụng một. Theo đặc tả kỹ thuật UML, bạn có thể chỉ định một mũi tên directionality trên hai đầu của các Hiệp hội ngành để chỉ hướng của truyền thông. Một số hiệp hội theo một hướng (ví dụ, nam diễn viên này quy định cụ thể thông tin cho các trường hợp sử dụng). Hầu hết các hiệp hội là hai chiều (có nghĩa là, diễn viên truy cập các trường hợp sử dụng, và các trường hợp sử dụng. | 94 Saturday Morning The Class diagram The Class diagram represents classes their component parts and the way in which classes of objects are related to one another. A class is a definition for a type of object. It s really not much different from what you find in a dictionary. If you want to find out what a widget is you look up the word widget. You would find a description of what a widget looks like its purpose and any other pertinent information for understanding widgets. There are no actual widgets in the dictionary only descriptions. There are no real objects in a class only descriptions of what a particular type of object looks like what it can do and what other objects it may be related to in some way. To document this information the Class diagram includes attributes operations stereotypes properties associations and inheritance. Attributes describe the appearance and knowledge of a class of objects. Operations define the behavior that a class of objects can manifest. Stereotypes help you understand this type of object in the context of other classes of objects with similar roles within the system s design. Properties provide a way to track the maintenance and status of the class definition. Association is just a formal term for a type of relationship that this type of object may participate in. Associations may come in many variations including simple aggregate and composite qualified and reflexive. Inheritance allows you to organize the class definitions to simplify and facilitate their implementation. Together these elements provide a rich set of tools for modeling business problems and software. However the Class diagram is still limited in what it can show you. Generally speaking it is a static view of the elements that make up the business or software. It s like a blueprint for a building or a piece of machinery. You can see the parts used to make it and how they are assembled but you cannot see how the parts will behave when you set them into motion.
