1. 1 Class Diagrams: The Essentials

2. 2 Terms and Concepts A class is... The most important building block of any object-oriented system. A description of a set of objects that share the same attributes and behaviors. A blueprint for creating an object. An abstraction (simplification) of reality. A representation of a software thing, a hardware thing, or even a conceptual thing. Graphically represented as a rectangle.

3. 3 Terms and Concepts All classes have … Names - Used to distinguish one class from another. A class must have a name. Attributes - Member data Operations (behaviors) - Member functions (C++) or methods (Java) Responsibilities Class names are … extracted from the problem domain (statement) nouns or noun phrases concise and descriptive

4. 4 Terms and Concepts Class operations (behaviors) are … named using a verb or verb phrases. inferred from the problem statement. Provide a requested service. usually notated using the format visibility name (parameter-list) : return-type {property-string} example: +printFirstName( ) : void Class responsibility… Is a contract or obligation of a class to the users of the class. Maps directly to the Responsibility field of a CRC card. CRC - Class Responsibility Collaboration

5. 5 Class Artifact

6. 6 Simple Class Diagram

7. 7 Common Modeling Techniques Identify the classes that are to be included in the design. Formulate a problem statement. The problem statement may be scenarios associated with use cases. Identify the nouns in the problem statement. Use CRC (Class, Responsibility, Collaboration) cards or use- cases to isolate each class. Determine the responsibilities of each class. Even out the work load between classes. A class with too much responsibility should be broken up into multiple classes. A class with too little responsibility should be absorbed into another class.

8. 8 Common Modeling Techniques Classes should exhibit high cohesion and low coupling. A class should have a single well-defined purpose. This promotes software reusability A class should interact with a limited number of other classes. This simplifies modifications to the program. Feel free to model abstract (non-software) things (such as people) that are outside of the system boundaries.

9. 9 Associations An association is … a type of relationship that can exist between one or more classes. used to show a ‘knows-a’ relationship. either unidirectional or bidirectional. graphically represented by a solid line which may optionally be labeled and have a name direction indicator or navigability arrows. an alternative notation for a class attribute

10. 10 Associations Associations may optionally have role names and multiplicity symbols on either end of the association line (next to the class icon). Role The face that a class on one end of an association presents to the class on the other end of the association. A class can participate in many associations and thus have multiple (different) roles. Role names are nouns. Role names are usually used in place of association names.

11. 11 Generalization Generalization is … a type of relationship that can exist between two classes. One of the classes is the base (or parent) class; the other class is the derived (or child) class. used to show a ‘kind-of’ relationship. another name for inheritance. graphically represented by a solid line with an open triangular arrowhead on the base class end. The parent class has no knowledge of the child class. All OO programming languages support single inheritance; some (C++) also support multiple inheritance.

12. 12 Notes and Comments Use notes to embed comments into UML diagrams. The comment may contain links to other documents. A note may stand alone or be attached to a graphical element. A dashed line is customarily used as the connector Use notes when a picture is not enough.

13. 13 Dependency A dependency is... A type of relationship that can exist between two classes. An indication that one class ‘uses’ another class. If the ‘used’ class changes it can have an impact on the ‘using’ class. Graphically represented as a dashed line with an open arrowhead on one end. Rarely labeled. The ‘used’ class is frequently an argument to one of the member functions of the ‘using’ class. The “used” class has no knowledge of the “using” class.

14. 14 Terms and Concepts