ITEC 3220A Using and Designing Database Systems Instructor: Prof Z. Yang Course Website: a.htm a.htm Office: TEL 3049

Object-Oriented Database

3 Object Orientation –Set of design and development principles –Based on autonomous computer structures known as objects OO Contribution areas –Programming Languages –Graphical User Interfaces –Databases –Design –Operating Systems

4 OO Concepts: Objects Abstract representation of a real-world entity –Unique identity –Embedded properties –Ability to interact with other objects and self OID –Unique to that object –Assigned by system at moment of object’s creation –Cannot be changed under any circumstances –Can be deleted only if the object is deleted –Can never be reused

5 Attributes (Instance Variables) Attributes: –Known as instance variables in OO environment Domain: –Logically groups and describes the set of all possible values that an attribute can have

6 Object State Set of values that object’s attributes have at a given time Can vary, although its OID remains the same To change the object’s state, change the values of the object’s attributes To change the object’s attribute values, send a message to the object –Message will invoke a method

7 Messages and Methods Method: –Code that performs a specific operation on object’s data –Protects data from direct and unauthorized access by other objects –Used to change the object’s attribute values or to return the value of selected object attributes –Represent real-world actions

8 Classes Collection of similar objects with shared structure (attributes) and behavior (methods) Class instance or object instance –Each object in a class

9 Object Characteristics

10 Class Hierarchy Superclass Subclass Class lattice

11 Inheritance Ability of object to inherit the data structure and behavior of classes above it Single inheritance –Class has one immediate superclass

12 Inheritance (Cont’d.) Multiple –Class has more than one immediate superclass

13 Abstract Data Types (ADT) Describes a set of similar objects Differs from conventional data types –Operations are user-defined –Uses encapsulation Definitions needed for creation –Name –Data representation –Abstract data type operations and constraints

14 Object Classification Simple –Only single-valued attributes –No attributes refer to other object Composite –At least one multivalued attribute –No attributes refer to other object Compound –At least one attribute that references other object Hybrid –Repeating group of attributes –At least one refers to other object Associative object

15 OO vs. E-R Model Components

16 Class-Subclass Relationship

17 Attribute-Class Link Object’s attribute references another object Relationship Representation –Related classes enclosed in boxes –Double line on right side indicates mandatory –Connectivity indicated by labeling each box 1:1 1:M M:N M:N with an Intersection Class Interobject Relationships

18 1:1 and 1:M Relationships

19 Employee-Dependent Relationship

20 Representing the M:N Relationship

21 Representing the M:N Relationship with Associated Attributes

22 Representing the M:N Relationship with Intersection Class

23 Late binding –Data type of attribute not known until runtime –Allows different instances of same class to contain different data types for same attribute Early binding –Allows database to check data type at compilation or definition time Late and Early Binding

24 Object, Entity, and Tuple –OODM object has behavior, inheritance, and encapsulation –OO modeling more natural Class, Entity Set, and Table –Class allows description of data and behavior –Class allows abstract data types Encapsulation and Inheritance –Object inherits properties of superclasses –Encapsulation hides data representation and method OODM vs. E-R Data Models

25 Object ID –Not supported in relational models Relationships –OODM Interclass references Class hierarchy inheritance –Relational models Value-based approach OODM vs. E-R Data Models (Cont’d) Access –Relational models SQL –OODM Navigational Set-oriented access

26 Example Using the following ERD to create the equivalent OO representations. Item_ID USER User_ID Checkout ITEM

27 More Example Assume the following business rules: A course contains many sections, but each section has only one course A section is taught by one professor, but each professor may teach one or more different sections of one or more course A section may contain many students, and each student is enrolled in many sections, but each section belongs to a different course. (Students my take many courses, but they cannot take many sections of the same course.) Each section is taught in one room, but each room may be used to teach several different sections of one or more courses A professor advises many students, but a student has only one advisor

28 More Example (Cont’d) Identify and describe the main classes of objects Modify your description in part 1 to include the use of abstract types such as Name, DOB, and Address Create the conceptual OO representations

29 More Example on OO Database Using intersection class to represent the following relationship

30 OO Design Example Design OO conceptual representations for an engineering company, using the following requirements: A customer has a customer identifier. Other important attributes of each customer include name and address. They can request any number of work orders from the company. The company maintains a list of materials. The data about materials include a material identifier, a name and cost. A work order has a work order number, a creation date, a completion date, a work address and a set of (one or more) tasks. In addition, each work order has one optional supervising employee. Each employee has a number assigned by the company. Other important attributes of each employee include name and skill. Each work order also has a collection of materials. The same material can be used by any number of work orders. Material requirement includes material quantity. Each task has a task identifier, a task name, an hourly rate and estimated hours. Tasks are standardized across work orders so that the same task may be performed on many work orders. We have to keep record of actual hours of each task on a work order.