Object-Oriented Database Management Systems

1. Object-Oriented Database Management Systems MOHAMMAD OMAR III YEAR CSE

2. What is Object Oriented Data Modeling? • Centers around objects and classes • Involves inheritance • Encapsulates both data and behavior • Benefits of Object-Oriented Modeling • Ability to tackle 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

3. Figure 14-1 – Phases of object-oriented systems development cycle

4. 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)

5. 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

6. 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

7. Figure 14-2 – UML class and object diagrams (a) Class diagram showing two classes Class diagram shows the static structure of an object-oriented model: object classes, internal structure, relationships.

8. (b) Object diagram with two instances Lamya : Student Lamya Object diagram shows instances that are compatible with a given class diagram.

9. Operations • A function or service that is provided by all instances of a class • Types of operators: • 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

10. 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).

11. Figure 14-3 – Association relationships of different degrees Lower-bound – upper-bound Represented as: 0..1, 0..*, 1..1, 1..*

12. Alternative multiplicity representation: specifying the two possible values in a list instead of a range Figure 14-4 – Examples of binary association relationships (a) University example

13. (b) Customer order example

14. 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

15. Binary association class with behavior Unary association with only attributes and no behavior Figure 14-6 – Association class and link object (a) Class diagram showing association classes

16. Association class instances (b) Object diagram showing link objects

17. Figure 14-7 –Ternary relationship with association class

18. Class-Level Attribute • Specifies a value common to an entire class, rather than a specific value for an instance. • Represented by underlining • “=“ is initial, default value.

19. Subclass, superclass • Subclass : Classes that are generalized • Superclass : The class in which the subclasses are generalized into.

20. 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 classes in different ways

21. This operation is abstract…it has no method at Student level Class-scope attributes – only one value common to all instances of these clases Methods are defined at subclass level Figure 14-11 – Polymorphism, abstract operation, class-scope attribute, and ordering

22. 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.

23. Restrict job placement Figure 14-12 – Overriding inheritance

24. 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.

25. Figure 14-13 Multiple inheritance

26. Aggregation • Aggregation: A part-of relationship between a component object and an aggregate object. • Composition: A stronger form of aggregation in which a part object belongs to only one whole object and exists only as part of the whole object. • Recursive Aggregation: composition where component object is an instance of the same class as the aggregate object.

27. Figure 14-14 – Example aggregation

28. Figure 14-15 – Aggregation and Composition (a) Class diagram (b) Object diagram

29. Object-Oriented Database Development

30. Object Definition Language (ODL) • Corresponds to SQL’s DDL (Data Definition Language) • Specify the logical schema for an object-oriented database • Based on the specifications of Object Database Management Group (ODMG)

31. Defining a Class • class – keyword for defining classes • attribute – keyword for attributes • operations – return type, name, parameters in parentheses • relationship – keyword for establishing relationship

32. Defining an Attribute • Value can be either: • Object identifier OR Literal • Types of literals • Atomic – a constant that cannot be decomposed into components • Collection – multiple literals or object types • Structure – a fixed number of named elements, each of which could be a literal or object type • Attribute ranges • Allowable values for an attribute • enum – for enumerating the allowable values

33. Kinds of Collections • Set – unordered collection without duplicates • Bag – unordered collection that may contain duplicates • List – ordered collection, all the same type • Array – dynamically sized ordered collection, locatable by position • Dictionary – unordered sequence of key-value pairs without duplicates

34. Defining Structures Structure = user-defined type with components struct keyword Example: struct Address { String street_address String city; String state; String zip; };

35. Defining Operations • Return type • Name • Parentheses following the name • Arguments within the parentheses

36. Defining Relationships • Only unary and binary relationships allowed • Relationships are bi-directional • implemented through use of inverse keyword • ODL relationships are specified: • relationship indicates that class is on many-side • relationship set indicates that class is on one-side and other class (many) instances unordered • relationship list indicates that class is on one-side and other class (many) instances ordered

37. Figure 15-1 –UML class diagram for a university database The following slides illustrate the ODL implementation of this UML diagram

38. Figure 15-2 –ODL Schema for university database

39. Figure 15-2 –ODL Schema for university database class keywordbegins the class definition.Class components enclosed between { and }

40. attribute has a data type and a name Figure 15-2 – ODL Schema for university database specify allowable values using enum

41. Figure 15-2 –ODL Schema for university database extent = the set of all instances of the class

42. Figure 15-2 –ODL Schema for university database Operation definition: return type, name, and argument list. Arguments include data types and names

43. Figure 15-2 –ODL Schema for university database relationship sets indicate 1:N relationship to an unordered collection of instances of the other class inverse establishes the bidirectionality of the relationship

44. Figure 15-2 –ODL Schema for university database relationship list indicates 1:N relationship to an ordered collection of instances of the other class

45. Figure 15-2 –ODL Schema for university database relationship indicates N:1 relationship to an instance of the other class

46. abstract class Student extends Employee{ ( …………. abstract float calc_tuition(); } Figure 15-5 –UML class diagram showing student generalization Note: abstract class denotes non-instantiable (complete constraint) Note: abstract operationdenotes no method (no implementation) of calc_tuition at the Student level

47. Creating Object Instances • Specify a tag that will be the object identifier • MBA699 course (); • Initializing attributes: • Cheryl student (name: “Cheryl Davis”, dateOfBirth:4/5/77); • Initializing multivalued attributes: • Dan employee (emp_id: 3678, name: “Dan Bellon”, skills {“Database design”, “OO Modeling”}); • Establishing links for relationship • Cheryl student (takes: {OOAD99F, Telecom99F, Java99F});

48. Querying Objects in the OODB • Object Query Language (OQL) • ODMG standard language • Similar to SQL-92 • Some differences: • Joins use class’s relationship name: • Select x.enrollment from courseofferings x, x.belongs_to y where y.crse_course = “MBA 664” and x.section = 1; • Using a set in a query • Select emp_id, name from employees where “Database Design” in skills;

49. Current ODBMS Products • Rising popularity due to: • CAD/CAM applications • Geographic information systems • Multimedia • Web-based applications • Increasingly complex data types • Applications of ODBMS • Bill-of-material • Telecommunications navigation • Health care • Engineering design • Finance and trading

50. XML (Extensible Markup Language) • XML is good not only for transmission of data from server to browser, it is also ideal for passing data from application to application and from machine to machine. • Since XML is database-neutral, it is likely that it will play a major role in connecting heterogeneous databases. Let's examine a number of different ways that XML can extend our Web solution set. • structured data - Any XML-aware application can extract exactly the info it needs (e.g., it can distinguish between instances of <AUTHOR>Paul McCartney</AUTHOR> and <BEATLES>Paul McCartney</BEATLES>). • XML complements HTML - XML and HTML can be combined, with each performing the portion of the task that it does best (e.g., XML data can be used to populate HTML forms or tables • self-describing - No prior knowledge of sender application is necessary because the syntax of an XML document instance describes the relationships among the various elements