Object-Oriented Data Modeling

1. Object-Oriented Data Modeling

2. Objects • Things • Software • Hardware • Person • Documents • etc.

3. Objects • Objects are representational constructs of entities • Objects encapsulate structural characteristics known as attributes and behavioral characteristics known as operations. • An object has a state. • State of an object is the condition of the object. • The state of a bank account object includes the current balance. • The state of a student includes whether s/he is a freshman, sophomore, junior, or senior. • An object is static in general. It does not change unless something changes from outside (via method) • It’s possible for some objects to change its own state. --- active objects. • e.g., clock

4. Objects • Every object is itself an instance of some class that defines the common set of attributes and methods that are shared by all instances of that class.  Class • HP C6150/N 34120098 is an object of class HPC6150.

5. Example of an HP C6150 All-In-One Printer :Attributes

6. Example of an Epson printer:Behavior (Methods) switchOn() switchOff() printDocument() formFeed() clearInkNozzle() changeInkCartridge() ReceiveFax()

7. Encapsulation • The idea of encapsulation stems from • the need to cleanly distinguish between the specification and the implementation of an operation • the need for modularity. • Modularity is necessary to structure complex applications designed and implemented by a team of programmers.

8. Encapsulation (cont.) • Encapsulation provides a form of ``logical data independence'‘ • We can change the implementation of a type without changing any of the programs using that type. • Thus, the application programs are protected from implementation changes in the lower layers of the system.

9. Encapsulation (cont.) • Proper encapsulation is obtained when only the operations are visible and the data and the implementation of the operations are hidden in the objects.

10. What is Object-Oriented Data Modeling? • Benefits of Object-Oriented Modeling • Ability to simplify challenging problems • Improved communication between users, analysts, designer, and programmers • Increased consistency in analysis and design • Explicit representation of commonality among system components • System robustness • Reusability of analysis, design, and programming results

12. OO vs. ER Data Modeling ER Object Oriented Class Entity type Object Entity instance Association Relationship Inheritance of attributes Inheritance of attributes Inheritance of behavior No representation of behavior Object-oriented modeling is frequently accomplished using the Unified Modeling Language (UML)

13. Object • An entity that has a well-defined role in the application domain, as well as state, behavior, and identity • Tangible: person, place or thing • Concept or Event: department, performance, marriage, registration • Artifact of the Design Process: user interface, controller, scheduler Objects exhibit BEHAVIOR as well as attributes  Different from entities

14. State, Behavior, Identity • State: attribute types and values • Behavior: how an object acts and reacts • Behavior is expressed through operations that can be performed on it • Identity: every object has a unique identity, even if all of its attribute values are the same

15. Class diagram shows the static structure of an object-oriented model: object classes, internal structure, relationships.

16. Object diagram shows instances that are compatible with a given class diagram.

17. Operations • A function or service that is provided by all instances of a class • Types of operations: • Constructor: creates a new instance of a class • Query: accesses the state of an object but does not alter its state • Update: alters the state of an object • Scope: operation applying to the class instead of an instance Operations implement the object’s behavior

18. Associations • Association: • Relationship among object classes • Association Role: • Role of an object in an association • The end of an association where it connects to a class • Multiplicity: • How many objects participate in an association. Lower-bound..Upper bound (cardinality)

19. Association relationships of different degrees Lower-bound – upper-bound Represented as: 0..1, 0..*, 1..1, 1..* Similar to minimum/maximum cardinality rules in ER

20. Alternative multiplicity representation: specifying the two possible values in a list instead of a range

22. Object diagram for customer order example

23. Association Class • An association that has attributes or operations of its own or that participates in relationships with other classes • Like an associative entity in ER model

25. Association class instances Association class and link object Object diagram showing link objects

26. Ternary relationship with association class

27. Derived attribute, association, and role Constraint expression for derived attribute Derived attribute Derived relationship (from Registers-for and Scheduled-for) Derived attributes and relationships shown with / in front of the name

28. Generalization/Specialization • Subclass, superclass • similar to subtype/supertype in ER • Common attributes, relationships, and operations • Disjoint vs. Overlapping • Complete (total specialization) vs. incomplete (partial specialization) • Abstract Class: no direct instances possible, but subclasses may have direct instances • Concrete Class: direct instances possible

29. An employee can only be one of these subclasses Shared attributes and operations An employee may be none of them. Specialized attributes and operations Examples of generalization, inheritance, and constraints Employee superclass with three subclasses

30. A patient MUST be EXACTLY one of the subtypes Examples of generalization, inheritance, and constraints Abstract patient class with two concrete subclasses Abstract indicated by italics Dynamic means a patient can change from one subclass to another over time

31. Class-Scope Attribute • Specifies a value common to an entire class, rather than a specific value for an instance. • Like static member in C++, C#, Java • Represented by underlining • “=“ is initial, default value.

32. Polymorphism • Abstract Operation: Defines the form or protocol of the operation, but not its implementation • Method: The implementation of an operation • Polymorphism: The same operation may apply to two or more different classes in different ways

33. This operation is abstract…it has no method at Student level Class-scope attributes – only one value common to all instances of these classes Methods are defined at subclass level Polymorphism, abstract operation, class-scope attribute, and ordering

34. Overriding Inheritance • Overriding: The process of replacing a method inherited from a superclass by a more specific implementation of that method in a subclass • For Extension: add code • For Restriction: limit the method • For Optimization: improve code by exploiting restrictions imposed by the subclass

35. Restrict job placement Overriding inheritance Subclasses that do not override place-student use the default behavior

36. Multiple Inheritance • Multiple Classification: An object is an instance of more than one class • Multiple Inheritance: A class inherits features from more than one superclass

37. Multiple inheritance