1 CS 426 Senior Projects Chapter 9: Relationships Chapter 10: Inheritance and Polymorphism [Arlow and Neustadt, 2002] February 27, 2007

2 Outline Relationships: Links Associations Dependencies Inheritance and Polymorphism: Generalization Class Inheritance Polymorphism

3 Relationships: Links & Associations Relationships = semantic connections between modeling elements Links = connections between objects Associations = connections between classes Links are instances of associations

4 Links.. A link is a connection between objects that communicate via messages Links can be: Unidirectional, if only one object (the source) contains a reference to the other (the target). Navigability is shown by an arrowhead at the target end of the link. Bidirectional, if both objects have a reference to the other. Bidirectional links are shown using unadorned lines with no arrowheads. Object diagrams show objects and their relationships at some point in time. Thus, links are dynamic connections between objects

5.Links. Example of object diagram, Fig. 9.2 [Arlow & Neustadt, 2002]. It shows objects, links, and roles. It also illustrates the “oblique” style of drawing paths in UML diagrams.

6..Links Example of unidirectional link, Fig. 9.3 [Arlow & Neustadt, 2002] The “orthogonal” style of drawing paths in UML diagrams, Fig. 9.4 [Arlow & Neustadt, 2002]

7 Associations: Semantics Associations are relationships between classes Links depend on associations, and instantiate them Fig. 9.5 [Arlow & Neustadt, 2002]

8 Associations: Syntax The syntax for an association includes: Association name Role names Multiplicity Navigability Example of association, Fig. 9.6 [Arlow & Neustadt, 2002]

9 Associations: Multiplicity.. Multiplicity constrains the number of objects of a class that can be involved in a given relationship at any point in time Fig. 9.8 [Arlow & Neustadt, 2002]

10 Associations:.Multiplicity. There is no default value for multiplicity in UML. If not specified, multiplicity is undecided Examples of multiplicity syntax, Table 9.1 [Arlow & Neustadt, 2002]

11 Associations:..Multiplicity Multiplicity constraints encode business rules of the model It is important to “read the model as written” Figure 9.9 [Arlow & Neustadt, 2002]

12 Associations: Hierarchies & Networks Example of association hierarchy, Fig [Arlow and Neustadt, 2002] Example of association network, Fig [Arlow and Neustadt, 2002]

13 Associations: Navigability Navigability can be read “messages can only be sent in the direction of the arrow” Relationships without arrows are bidirectional Unidirectional associations reduce coupling between classes Fig [Arlow & Neustadt, 2002]

14 Associations: Modeled using Attributes One-to-one and one-to-many associations can be modeled using attributes Fig [Arlow & Neustadt, 2002]

15 Associations: Association Classes. Many-to-many associations can lead to association classes Example of many-to-many association, Fig [Arlow & Neustadt, 2002] Corresponding association class, Fig [Arlow & Neustadt, 2002]

16 Associations:.Association Classes However, many-to-many associations can also be modeled using regular classes, e.g., Fig [Arlow & Neustadt, 2002]

17 Dependencies: Definition and Types. “A dependency is a relationship between two elements where a change to one element (the supplier) may affect or supply information needed by the other element (the client)” [Rumbaugh et al., The UML Reference Manual] Four types of dependency Table 9.2 [Arlow & Neustadt, 2002]

18 Dependencies:.Definition and Types Examples of different types of dependencies Fig [Arlow and Neustadt, 2002]

19 Dependencies: Usage dependencies The > dependencies are the most common type of dependency. They state that the client makes use of the supplier in some way. Example, Fig [Arlow & Neustadt, 2002] Fig Java code for the above example

20 Dependencies: Abstraction dependencies Abstraction dependencies are dependencies between model elements that are at different level of abstraction. Examples, Table 9.3 [Arlow & Neustadt, 2002]

21 Dependencies: Permission dependencies Permission dependencies indicate the capability of one model element to access another model element. Examples of permission dependencies: >

22 Generalization Generalization applies to all classifiers and to some other elements such as associations, states, and events Example of generalization, Fig [Arlow & Neustadt, 2002]

23 Inheritance: Overriding. Example of class hierarchy, Fig [Arlow & Neustadt, 2002]

24 Inheritance:.Overriding Example of overriding, Fig [Arlow & Neustadt, 2002]

25 Inheritance: Abstract Classes & Operations Example of abstract classes and operations, Fig [Arlow & Neustadt, 2002]

26 Inheritance: Level of Abstraction In generalization hierarchies it is important to maintain a uniform level of abstraction at each level Incorrect example, Fig [Arlow & Neustadt, 2002]

27 Polymorphism… Polymorphism means “many forms”. A polymorphic operation has several different implementations Example of polymorphism, Fig [Arlow & Neustadt, 2002]

28.Polymorphism.. Example of polymorphism “in action,” Fig [Arlow & Neustadt, 2002]

29..Polymorphism. Object diagram with polymorphism, Fig [Arlow & Neustadt, 2002]

30 …Polymorphism Another example of polymorphism, Fig [Arlow & Neustadt, 2002]