Lecture on Object Oriented Databases Database Systems Design
Lecture on Object Oriented Databases Database Systems: Design, Implementation, and Management, Fifth Edition, Rob and Coronel www. assignmentpoint. com
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 www. assignmentpoint. com
Object Orientation • 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 www. assignmentpoint. com
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 www. assignmentpoint. com
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 www. assignmentpoint. com
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 www. assignmentpoint. com
OO Concepts: Objects (con’t. ) • Class hierarchy – Code that performs operation on object’s data – Has name and body www. assignmentpoint. com
Object Characteristics Figure 11. 7 www. assignmentpoint. com
Class Hierarchy • Superclass • Subclass • Class lattice Figure 11. 8 www. assignmentpoint. com
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 www. assignmentpoint. com
Inheritance (con’t. ) • Multiple – Class has more than one immediate superclass Figure 11. 10 www. assignmentpoint. com
Method Overriding • Method redefined at subclass level Figure 11. 12 www. assignmentpoint. com
Polymorphism Allows different objects to respond to same message in different ways Figure 11. 13 www. assignmentpoint. com
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 www. assignmentpoint. com
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 www. assignmentpoint. com
Characteristics of OODM • • • Supports complex objects Must be extensible Supports encapsulation Exhibit inheritance Supports object identity www. assignmentpoint. com
OO vs. E-R Model Components Table 11. 3 www. assignmentpoint. com
Shared Representation for all Objects of the Class Person Figure 11. 14 Figure 11. 15 www. assignmentpoint. com
Referential Sharing of Objects Figure 11. 19 www. assignmentpoint. com
Class-Subclass Relationship Figure 11. 21 Figure 11. 20 www. assignmentpoint. com
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 with an Intersection Class www. assignmentpoint. com
1: 1 and 1: M Relationships Figure 11. 24 www. assignmentpoint. com
Employee-Dependent Relationship Figure 11. 25 www. assignmentpoint. com
Representing the M: N Relationship Figure 11. 26 www. assignmentpoint. com
Representing the M: N Relationship with Associated Attributes Figure 11. 27 www. assignmentpoint. com
Representing the M: N Relationship with Intersection Class Figure 11. 28 www. assignmentpoint. com
Object Space Representation Figure 11. 29 www. assignmentpoint. com
Late and Early Binding • 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 www. assignmentpoint. com
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 www. assignmentpoint. com
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 www. assignmentpoint. com • Access – Relational models • SQL – OODM • Navigational • Set-oriented access
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 www. assignmentpoint. com
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 www. assignmentpoint. com
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 www. assignmentpoint. com
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 www. assignmentpoint. com
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) www. assignmentpoint. com
The Next Generation of DBMS • • • Object-oriented database systems Artificial intelligence systems Expert systems Distributed database The Internet www. assignmentpoint. com
- Slides: 36