UML建模技术第5章

Figure 5-3. Generalization
5.2.3 Associations




An association is a structural relationship that specifies that objects of one thing are connected to objects of another. It's quite legal to have both ends of an association circle back to the same class. An association that connects exactly two classes is called a binary association. Although it's not as common, you can have associations that connect more than two classes; these are called n-ary associations.

With care, most line crossings can be avoided. If a line crossing is necessary and there is ambiguity about how the paths are connected, a small arc can be used to indicate a line crossing.
Chapter 5. Relationships



Dependency, generalization, and association relationships Modeling simple dependencies Modeling single inheritance Modeling structural relationships Creating webs of relationships


Dependencies Associations Generalizations
5.2 Terms and Concepts
A
relationship is a connection among things. Graphically, a relationship is rendered as a path, with different kinds of lines used to distinguish the kinds of relationships. dependency generalization association
Figure 5-6. Multiplicity
4) Aggregation


This kind of relationship is called aggregation, which represents a "has-a" relationship, meaning that an object of the whole has objects of the part. Aggregation is really just a special kind of association and is specified by adorning a plain association with an unfilled diamond at the whole end, as shown in Figure 5-7.

Graphically, an association is rendered as a solid line connecting the same or different classes.
Figure 5-4. Association Names
1) Name


An association can have a name, and you use that name to describe the nature of the relationship. So that there is no ambiguity about its meaning, you can give a direction to the name by providing a direction triangle that points in the direction you intend to read the name, as shown in Figure 5-4.
Figure 5-7. Aggregation
5.2.4 Other Features


Plain, unadorned dependencies, generalizations, and associations with names, multiplicities, and roles are the most common features you'll need when creating abstractions. Sometimes, however, you'll need to visualize or specify other features, such as composite aggregation, navigation, discriminants, association classes, and special kinds of dependencies and generalizations.


It is written as an expression with a minimum and maximum value, which may be the same; two dots are used to separate the minimum and maximum values. You can show a multiplicity of exactly one (1), zero or one (0..1), many (0..*), or one or more (1..*). You can give an integer range (such as 2..5). You can even state an exact number (for example, 3, which is equivalent to 3..3).
5.2.5 Drawing Styles

Typically, modelers choose one of two styles for drawing lines:

Oblique lines at any angle. Rectilinear lines drawn parallel to the sides of the page.
5.2.1 Dependencies



A dependency is a relationship that states that one thing (for example, class Window) uses the information and services of another thing (for example, class Event), but not necessarily the reverse. Graphically, a dependency is rendered as a dashed directed line, directed to the thing being depended on. Choose dependencies when you want to show one thing using another.
Figure 5-2. Dependencies
5.2.2 Generalizations



A generalization is a relationship between a general kind of thing (called the superclass or parent) and a more specific kind of thing (called the subclass or child). Generalization is sometimes called an "is-akind-of" relationship. Use generalizations when you want to show parent/child relationships.
2) Role



When a class participates in an association, it has a specific role that it plays in that relationship; A role is just the face the class at the far end of the association presents to the class at the near end of the association. The role played by an end of an association is called an end name (in UML1, it was called a role name).
5.1 Getting Started


In the UML, the ways that things can connect to one another, either logically or physically, are modeled as relationships. In object-oriented modeling, there are three kinds of relationships that are most important: