Object Oriented Database and UML

1. Object Oriented Database and UML MIS 304 Winter 2006

2. And now for Something Completely Different…

3. Class Objective • Understand the basic concepts of Object Orientation. • Understand how the OO approach differs from the Relational approach. • Apply the concepts of OO to Database management. • Understand the UML Modeling Language and how it applies to databases

4. Object Orientation and Its Benefits • Object orientation is a modeling and development methodology based on object-oriented (OO) concepts. • Definition of Object Orientation:A set of design and development principles based on conceptually autonomous computer structures known as objects. Each object represents a real-world entity with the ability to interact with itself and with other objects. • Think of objects as “Nouns” with the “Verbs” already attached to them.

6. The History of Object Orientation Video

7. Additional Information on PARC • Dealers of Lightning: Xerox PARC and the Dawn of the Computer Age , Michael Hiltzik, Texere, 2001, ISBN 1842030000 • Triumph of the Nerds, Robert Cringley, PBS, 1995.

8. The Evolution of OO Concepts • From traditional to object-oriented programming (OOP) • Before OOP, data and procedures were isolated from each other. Data were treated as the passivecomponent, while procedures manipulated the data as the active component. • Procedural languages (e.g., COBOL) encouraged the rigid distinction between data and procedure. • In an OOP environment, the programmer asks Objects to perform operations on themselves. • OO concepts first appeared in some programming languages and set the stage for more refined OO concepts.

9. The Evolution of OO Concepts • Main Objectives of Object-Oriented Programming Languages (OOPL) • To provide an easy-to-use software development environment. • To provide a powerful software modeling tool for applications prototyping. • To decrease development time by reducing the amount of code. • To improve programmer productivity by making that code reusable.

10. The Evolution of OO Concepts • Important Attributes of OO Environment • The data set is no longer passive. • Data and procedures are bound together, creating an object. • The object has an innate ability to act on itself.

11. Object-Oriented Concepts • Overview • Objects: Components and Characteristics • Object Identity • Attributes (Instance Variables) • Object State • Messages and Methods • Classes • Protocol • Superclasses, Subclasses, and Inheritance • Methods Overriding and Polymorphism • Abstract Data Types • Object Classification

12. Object-Oriented Concepts • Objects: Components and Characteristics An object is an abstract representation of a real-world entity that has a unique identity, embedded properties, and the ability to interact with other objects and itself.

13. Object-Oriented Concepts • Object Identity • The object’s identity is represented by an object ID (OID), which is unique to that object. • The OID is assigned by the system at the moment of the object’s creation and cannot be changed under any circumstance. • The OID can be deleted only if the object is deleted, and that OID can never be reused.

14. Object Identity • Based on an Object Identifier (OID) • Must be guaranteed to be unique in the space in which the object exists. • Syntax options • Dotted 1.2.3.4.5.6.7 • GUID Semi-Random number {}

15. Object-Oriented Concepts • Attributes (Instance Variables) • Objects are described by their attributes, known as instance variables. (See Table 11.2) • Attributes have a domain. The domain logically groups and describes the set of all possible values that an attribute can have. • An attribute can be single valued or multivalued. • Attributes may reference one or more other objects.

16. Object Attributes

17. Object-Oriented Concepts • Object State • The object stateis the set of values that the object’s attributes have at a given time. • If we change the object’s state, we must change the values of the object attributes. • To change the object’s attribute values, we must send a message to the object. • This message invokes a method.

18. Object-Oriented Concepts • Messages and Methods • Every operation performed on an object must be implemented by a method. • Methods represent real-world actions and are equivalent to procedures in traditional programming languages. • Every method is identified by a name and has a body. • The body is composed of computer instructions written in some programming language to represent a real-world action.

19. Object-Oriented Concepts • Messages and Methods • To invoke a method you send amessage to the object. • A message is sent by specifying a receiver object, the name of the method, and any required parameters. • The internal structure of the object cannot be accessed directly by the message sender. The ability to hide the object’s internal details (attributes and methods) is known as encapsulation. • An object may send messages to change or interrogate another object’s state. (See Figure 11.3)

20. Objects Send Messages To Each Other

21. Object-Oriented Concepts • Classes • Objects that share common characteristics are grouped into classes. A class is a collection of similar objects with shared structure (attributes) and behavior (methods). • Each object in a class is known as a class instance or object instance. (See Figure 11.4) • Classes are general and extensible • Example: STUDENT class (See Figure 11.5)

22. Class Illustration Animal Living Vertebrates Living Backbone

23. Representation Of The Class Student

24. Object-Oriented Concepts • Protocol • The class’s collection of messages, each identified by a message name, constitutes the object or class protocol. • The protocol represents an object’s public aspect; i.e., it is known by other objects as well as end users. • The implementation of the object’s structure and methods constitutes the object’s private aspect. • A message can be sent to an object instance or the class. When the receiver object is a class, the message will invoke a class method.

25. Public and Private Aspects Of An Object

26. Flashlights Demo • Example of basic OO concepts

27. OO Summary: Object Characteristics

28. Object-Oriented Concepts • Superclasses, Subclasses, and Inheritance • Classes are organized into a class hierarchy. • Example: Musical instrument class hierarchy (Figure 11.8) • Piano, Violin, and Guitar are a subclass of Stringed instruments, which is, in turn, a subclass of Musical instruments. • Musical instruments defines the superclass of Stringed instruments, which is, in turn, the superclass of the Piano, Violin, and Guitar classes. • Inheritance is the ability of an object within the hierarchy to inherit the data structure and behavior (methods) of the classes above it.

29. Musical Instruments Class Hierarchy

30. Object-Oriented Concepts • Two variants of inheritance: • Single inheritance exists when a class has only one immediate superclass above it. • Most of the current OO systems support single inheritance. • When the system sends a message to an object instance, the entire hierarchy is searched for the matching method in the following sequence: • Scan the class to which the object belongs. • If the method is not found, scan the superclass. • The scanning process is repeated until either one of the following occurs: • The method is found. • The top of the class hierarchy is reached without finding the message.

31. Single Inheritance

32. Object-Oriented Concepts • Two variants of inheritance: • Multiple inheritance allow a class to be derived from several parent superclasses located above that class. • Single inheritance exists when a class has only one immediate (parent) superclass above it.

33. Motor Vehicle And Bicycle Instance Variables

34. Object-Oriented Concepts • Method Overriding and Polymorphism • We may override a superclass’ method definition by redefining the method at the subclass level. (See Figure 11.12) • Polymorphism allows different objects to respond to the same message in different ways. (See Figure 11.13)

35. Employee Class Hierarchy Method Override

36. Employee Class Hierarchy Polymorphism

37. Object-Oriented Concepts • Object Classification • A simple object contains only single-valued attributes and none of its attributes refer to another object. • A composite object contains at least one multivalued attribute and none of its attributes refer to another object. • A compound object contains at least one attribute that references another object. • A hybrid object contains a repeating group of attributes, and at least one of the repeating attributes refers to another object. • An associative object is used to represent a relationship between two or more objects.

38. Characteristics of an OO Data Model • An Object-Oriented Data Model Must: • Support the representation of complex objects. • Be extensible; i.e., it must be capable of defining new data types as well as the operations to be performed on them. • Support encapsulation; i.e., the data representation and the method’s implementation must be hidden from external entities. • Exhibit inheritance; an object must be able to inherit the properties (data and methods) of other objects. • Support the notion of object identity (OID).

39. How do you apply these concepts to Databases?

40. OO And E-R Model Components

41. OODM and Previous Data Models • Object, Entity, and Tuple • An OODM object has additional characteristics such as behavior, inheritance, and encapsulation. • Such characteristics make OO modeling much more natural than E-R and relational modeling.

42. An Invoice Representation But remember the object has “methods” attached to it too.

43. OODM and Previous Data Models • Class, Entity Set, and Table • Class is a more powerful concept that allows not only the description of the data structure but also the description of the behavior. • A class allows both the concept and the implementation of abstract data types. • Encapsulation and Inheritance • An object belonging to a class inherits all the properties of its superclasses. • Encapsulation hides the data representation and the method’s implementation from other objects and the user.

44. OODM and Previous Data Models • Object ID • Object ID is not supported in either the E-R model or the relational model. • The hierarchical and the CODASYL models support some form of ID. • Relationships • Relationships in an OODM can be of two types: interclass references or class hierarchy inheritance. • E-R and relational models use a value-based relationship approach.

45. OODM and Previous Data Models • Access • E-R and relational models use an ad hoc, set-oriented query language. • OODM is suited to support both navigational and set-oriented access.

46. Object-Oriented DBMS

47. The Thirteen OODBMS Rules

48. How OO Affects Database Design • OO database design approach provides both the data identification and the procedures or data manipulation to be performed. • OO database design forces us to think of data and procedures as a self-contained entity. • OO design is iterative and incremental in nature. • DBA’s role is likely to change with more programming responsibilities. • Lack of standards affects OO database design.

49. OODBMS: Advantages and Disadvantages • Advantages • More semantic information. • Support for complex objects. • Extensibility of data types. • Improved performance with efficient caching. • Versioning. • Faster development and easy maintenance through inheritance and reusability. • Technology-driven product for next generation DBMS. • Potential to integrate DBMSs into a single environment.

50. OODBMS: Advantages and Disadvantages • Disadvantages • Strong opposition from the established players. • Lack of theoretical foundation. • Retrogressive to the old pointer systems. • Lack of standard ad hoc query language. • Lack of business data design and management tools. • Steep learning curve. • Lack of resources.