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Object-Oriented Analysis and Design with UML2 and Rational Software Modeler

Object-Oriented Analysis and Design with UML2 and Rational Software Modeler. 03. Classes, Relationships and Packages. Where Are We?. Associations Dependencies Generalizations Packages Miscellaneous Topics. Classes Collaborate. Objects collaborate with each other by sending messages

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Object-Oriented Analysis and Design with UML2 and Rational Software Modeler

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  1. Object-Oriented Analysis and Design with UML2 and Rational Software Modeler 03. Classes, Relationships and Packages

  2. Where Are We? • Associations • Dependencies • Generalizations • Packages • Miscellaneous Topics

  3. Classes Collaborate • Objects collaborate with each other by sending messages • To send a message to an object, the client object must have a link with the supplier • If there is a link between two objects, there must be some kind of relationship between the corresponding classes: • The relationship may be a structural relationship: association and its variants (aggregation, composition) • Or a non-structural relationship, called a dependency

  4. What Is an Association? • The semantic relationship between two or more classifiers that specifies connections among their instances • A structural relationship specifying that objects of one thing are connected to objects of another thing

  5. What is Navigability? • Navigability indicates that it is possible to navigate from one class to another (or more precisely from one instance of a class to another instance of the same class or of another class) • Associations are bi-directional by default • An association with an arrow is a one-way association • The client class can navigate to the supplier class, but not the other way around Association navigable from RegistrationController to Schedule Association navigable in both directions

  6. Naming Associations • To clarify its meaning, an association can be named • The name is represented by a label as shown below • Usually a verb or an expression starting with a verb

  7. Association Roles • A role name specifies the role that a class plays in its relationship with another class • Role names are typically names or noun phrases • A role name is placed near the association next to the class to which it applies (as a role) • Each association end may be named

  8. What Is Multiplicity? • Multiplicity is the number of instances one class relates to ONE instance of another class • For each association, there are two multiplicity decisions to make, one for each end of the association • For each instance of Professor, many Course Offerings may be taught • For each instance of Course Offering, there may be either one or zero Professor as the instructor

  9. Multiplicity Indicators • Unspecified • Exactly one • Zero or more (no upper limit) • One or more • Zero or one (optional) • Specific range • Multiple, disjoint ranges 1 0..* * 1..* 0..1 2..4 2, 4..6

  10. Example

  11. Association Classes • Take the n-n relationship between Student and Course • If you have to capture the grade received by a student for a given course, where would you place the grade? On Student? On Course? • The answer is on the association itself by adding an association class, called Result • The association class represents the association of exactly one student and one course

  12. Qualified Associations • A qualifier is an attribute of an association whose values partition the set of objects related to an object across an association • A qualified association represents a lookup table (which can be implemented as a hash table for instance) • The multiplicity of the target class is often 0..1 but it may be 0..* • Example: • In the context of the WorkDesk, you’d have a jobId that would identify a particular ReturnedItem. In that sense, jobId is an attribute of the association. Then, given an object of type WorkDesk and a particular value for jobId, you can navigate to 0 or 1 object of type ReturnedItem.

  13. What Is an Aggregation? • A special form of association that models a whole-part relationship between the aggregate (the whole) and its parts • An aggregation is an “is a part-of” relationship • Multiplicity is represented like other associations

  14. What Is a Composition? • A form of aggregation with strong ownership and coincident lifetimes • The parts cannot survive the whole/aggregate

  15. Example

  16. Where Are We? • Associations • Dependencies • Generalizations • Packages • Miscellaneous Topics

  17. What Is A Dependency? • A non-structural relationship between two classes • The client needs access to the services provided by the supplier • But doesn’t need to maintain a permanent relationship with the supplier objects (transient relationship) • A dependency may result from: • A local declaration within the body of an operation (op1 below) • The supplier appears as a parameter type (op2 in the example) publicclass Client { publicvoid op1() { Supplier localVar = new Supplier(); …

  18. Where Are We? • Associations • Dependencies • Generalizations • Packages • Miscellaneous Topics

  19. What Is Generalization? • A relationship among classes where one class shares the structure and/or behavior of one or more classes • A subclass inherits its parent’s attributes, operations, and relationships • A subclass may: • Add additional attributes, operations, relationships • Redefine inherited operations (use caution!) • Defines a hierarchy of abstractions in which a subclass inherits from one or more super-classes • Is an “is a kind of” relationship • Single or multiple inheritance

  20. Example Superclass, parent or ancestor Subclasses, children or descendants Generalization Relationship

  21. What is an Abstract Class? • Abstract classes cannot be instantiated • Name in italics • Abstract operations: the subclasses must provide the implementation • Name in italics Abstract Class Abstract Operation All objects are either lions or tigers

  22. What Is An Interface? • A “contract” between providers and consumers of services • Equivalent to an abstract class in which all operations are abstract • Provided interfaces: interfaces the element exposes to its environment • Required interfaces: interfaces the element requires from other elements • Note: UML interfaces can have attributes (not possible for Java interfaces) • The provider of the interface is said to realize the interface Interface Realization New in UML2 Interface Ball and Socket notation: see module 4

  23. What Is Polymorphism? • The ability to hide many different implementations behind a single class or interface Without polymorphism: Shape s = …; If (s instanceof Rectangle) { ((Rectangle) s).draw(); else if (s instanceof Circle) { ((Circle) s).draw(); else if (s instanceof Triangle) { ((Circle) s).draw(); } With polymorphism: Shape s = …; s.draw();

  24. Where Are We? • Associations • Dependencies • Generalizations • Packages • Miscellaneous Topics

  25. What Is a Package? • A general purpose mechanism for organizing elements into groups • A model element that can contain other model elements • Grouping of logically related elements • A package can be used: • To organize the model under development • As a unit of configuration management

  26. Package Relationships • A package A depends on a package B if there is at least one element from A that depends on at least one element from B ClassA1 depends on ClassB1 (any relationship between two elements implies a dependency and the arrow indicates the direction of the dependency) Dependency

  27. Where Are We? • Associations • Dependencies • Generalizations • Packages • Miscellaneous Topics

  28. What Is A Stereotype? • A stereotype is a mechanism used to extend the vocabulary of UML • Represented textually (<<mystereo>>) and/or graphically • Any UML element may be stereotyped • Stereotypes are grouped into collections of stereotypes, called profiles • Can be defined for specific domains and/or applications • Pre-defined or custom • A stereotype may have its own properties

  29. More About Element Visibility • public (+) • Visible to all elements that can access the contents of the namespace that owns it • private (-) • Only visible inside the namespace that owns it • protected (#) • Visible to elements that have a generalization relationship to the namespace that owns it • package (~) • Only named elements that are not owned by packages can be marked as having package visibility • Any element marked as having package visibility is visible to all elements within the nearest enclosing package

  30. Classifier Scope • Determines number of instances of the attribute/operation • Instance: one instance for each class instance • Classifier: one instance for all class instances • Classifier scope is denoted by underlining the attribute/operation name • “Static” attributes and operations in languages like Java and C++ public static CourseCatalog getInstance() { If (instance == null) { instance = new CourseCatalog(); } return instance; } Pattern “Singleton” And some client code: CourseCatalog cat = CourseCatalog.getInstance(); CourseList courses = cat.retrieveCourses();

  31. Structure Diagrams • Structure Diagrams show the static structure of the objects in a system • Class diagrams typically show classes and relationships between classes • Most of the diagrams we have used so far are class diagrams • Package diagrams typically show packages and relationships between packages • Object diagrams typically show objects (instances of classes) and links between objects (instances of relationships between classes) • The other structure diagrams (composite structure, component and deployment are presented in module 4) • There are no strict boundaries between different variations • It is possible to display any element you normally display in a given structure diagram in any variation.

  32. Object Diagram: Example Object diagrams are often used to conceptualize the more abstract class diagrams by providing “real-world” examples of objects and object connections An object diagram also represent a snapshot of the system at a given time, highlighting existing and non-existing links: Here boris needs to establish a link with PM to deliver parcel1 …

  33. What Is A Constraint? • A condition or restriction (a Boolean expression) expressed in natural language text or in a machine readable language for the purpose of declaring some of the semantics of an element • Some are predefined in UML (“xor”), others may be user-defined • OCL (Object Constraint Language) is a predefined language for writing constraints

  34. Exercise • Perform the exercise provided by the instructor

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