Object-Oriented Databases Chapter 11 Object-Oriented Databases Database Systems: Design, Implementation, and Management, Fifth Edition, Rob and Coronel

In this chapter, you will learn: What basic concepts govern OO systems What effect OO concepts are likely to have on data modeling and design How OO features are related to the more traditional relational and E-R models What the basic features of an OO database management system (OODBMS) are About the advantages and disadvantages of OODBMSs Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Object Orientation Object Orientation OO Contribution areas 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 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Evolution of OO Concepts Concepts stem from object-oriented programming languages (OOPLs) Ada, ALGOL, LISP, SIMULA OOPLs goals Easy-to-use development environment Powerful modeling tools for development Decrease in development time Make reusable code OO Attributes Data set not passive Data and procedures bound together Objects can act on self Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

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 object Not a primary key Attributes Called instance variables Domain Object state Object values at any given time Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OO Concepts: Objects (con’t.) Methods Code that performs operation on object’s data Has name and body Messages Invokes method Sent to object Classes Collection of similar objects Shares attributes and structure Protocol Represents object’s public aspect Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OO Concepts: Objects (con’t.) Class hierarchy Code that performs operation on object’s data Has name and body Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Object Characteristics Figure 11.7 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Class Hierarchy Superclass Subclass Class lattice Figure 11.8 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Inheritance Ability of object to inherit the data structure and behavior of classes above it Single inheritance Class has one immediate superclass Figure 11.9 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Inheritance (con’t.) Multiple Class has more than one immediate superclass Figure 11.10 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Method Overriding Method redefined at subclass level Figure 11.12 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Polymorphism Allows different objects to respond to same message in different ways Figure 11.13 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

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 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Object Classification Simple Only single-valued attributes No attributes refer to other object Composite At least one multivalued attribute Compound At least one attribute that references other object Hybrid Repeating group of attributes At least one refers to other object Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Characteristics of OODM Supports complex objects Must be extensible Supports encapsulation Exhibit inheritance Supports object identity Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OO vs. E-R Model Components Table 11.3 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Shared Representation for all Objects of the Class Person Figure 11.14 Figure 11.15 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Referential Sharing of Objects Figure 11.19 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Class-Subclass Relationship Figure 11.21 Figure 11.20 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Interobject Relationships 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:M M:N M:N with an Intersection Class Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

1:1 and 1:M Relationships Figure 11.24 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Employee-Dependent Relationship Figure 11.25 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Representing the M:N Relationship Figure 11.26 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Representing the M:N Relationship with Associated Attributes Figure 11.27 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Representing the M:N Relationship with Intersection Class Figure 11.28 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Object Space Representation Figure 11.29 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

Late and Early Binding Late binding Early 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 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OODM vs. E-R Data Models 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 Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OODM vs. E-R Data Models (con’t.) Object ID Not supported in relational models Relationships OODM Interclass references Class hierarchy inheritance Relational models Value-based approach Access Relational models SQL OODM Navigational Set-oriented access Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OODBMS Database management system integrates benefits of typical database systems with OODM characteristics Handles a mix of data types Follows OO rules Follows DBMS rules Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OO and Database Design Provides data identification and the procedures for data manipulation Data and procedures self-contained entity Iterative and incremental DBA does more programming Lack of standards Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OODBMS Advantages More semantic information Support for complex objects Extensibility of data types May improve performance with efficient caching Versioning Reusability Inheritance speeds development and application Potential to integrate DBMSs into single environment Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OODBMS Disadvantages Strong opposition from the established RDBMSs Lack of theoretical foundation Throwback to old pointer systems Lack of standard ad hoc query language Lack of business data design and management tools Steep learning curve Low market presence Lack of compatibility between different OODBMSs Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

OO Influences on Relational Model Extensibility of new user-defined (abstract) data types Complex objects Inheritance Procedure calls (rules or triggers) System-generated identifiers (OID surrogates) Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

The Next Generation of DBMS Object-oriented database systems Artificial intelligence systems Expert systems Distributed database The Internet Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel