McGraw-Hill/Irwin Copyright © 2007 by The McGraw-Hill Companies, Inc. All rights reserved. Chapter 18 Object Database Management Systems

18-2 Outline  Motivation for object database management  Object-oriented principles  Architectures for object database management  Object database definition and manipulation in SQL:2003  Object database definition and manipulation in Oracle 10g

18-3 Motivation: Complex Data  Most relational DBMSs support only a few data types.  Many business applications require large amounts of complex data such as images, audio, and video.  Integration of complex data with simple data drives the demand for object database technology

18-4 Motivation: Type System Mismatch  Increasing use of database access in procedural code  Different data types used in programming languages versus DBMSs  Data type mismatch makes software more difficult to develop.  A relational DBMS cannot perform elementary operations on complex data.

18-5 Application Examples  Dental Office Support  Real Estate Listing Service  Auto Insurance Claims

18-6 Object-Oriented Principles  An object is a combination of data and procedures.  A class is a prototype that defines the variables and methods common to all objects of the class.  Three underlying principles: encapsulation, inheritance and polymorphism.

18-7 Encapsulation  Objects can be accessed only through their interfaces.  Classes can be reused rather than just individual procedures.  More complex classes can be defined using simpler classes.  Provides a form of data independence.

18-8 Bond Class Example CLASS Bond { // VARIABLES: ATTRIBUTE Float IntRate; ATTRIBUTE Date Maturity; // METHODS: Float Yield(); // Computes the Bond’s Yield };

18-9 Inheritance  Sharing of data and code among similar classes (classes and subclasses).  Inherit variables and methods from parent classes  Use methods and variables of ancestor classes  Provides an improved organization of software and incremental reusability.

18-10 Inheritance Examples

18-11 Multiple Inheritance Example

18-12 Polymorphism  Ability to choose among multiple implementations  Benefits  Incremental modification of code  Smaller vocabulary of method names  Requesting a method execution involves sending a message to an object  Client-server processing and object- oriented computing are closely related.

18-13 Processing a Message

18-14 Binding  Associating an implementation with a message  Static binding  Performed at compile-time  More efficient but less flexible  Dynamic binding  Performed at run-time (late binding)  More flexible but less efficient

18-15 Strong Type Checking  Complex expressions can involve many methods and objects  Incompatibility errors common in code  Ability to ensure that programming code contains no incompatibility errors  An important kind of error checking for object-oriented coding

18-16 Programming Languages versus DBMSs  Programming languages have used object-oriented principles for many years.  Programming languages emphasize software maintenance and code reusability.  Object DBMSs are more recent.  Relax encapsulation to reference an object’s data in a query.  Simpler inheritance mechanisms in DBMSs

18-17 Object Database Architectures  Adding object-oriented features to a DBMS is a good idea  Many approaches about the features to add and how features should be added.  Some approaches provide small extensions that leave object features outside the DBMS.  Other approaches involve a complete rewrite of the DBMS to accommodate objects  Marketplace will determine best approaches

18-18 Large Objects and External Software  Large object storage along with external software to manipulate large objects  BLOB and CLOB data types  The large object approach is simple to implement and universal.  The large object approach suffers from serious performance drawbacks.

18-19 Large Object Architecture

18-20 Specialized Media Servers  Dedicated server manages complex data  Application programming interface (API) to access complex data.  Good performance for specific kinds of complex data  Limited range of operations supported  Poor performance when combining simple and complex data

18-21 Specialized Media Server Architecture

18-22 Object database middleware  Middleware to manage complex data stored outside of a database along with traditional data stored in a database  Integrate complex data stored on PCs and remote servers with relational databases  Possible performance problems because of a lack of integration with a DBMS.

18-23 Object Middleware Approach

18-24 Object-Relational DBMS  A relational DBMS extended with an object query processor for user-defined data types  User-defined types for complex data  User-defined functions in SQL statements  SQL:2003 standard  Good integration of complex data with reliability of relational DBMS

18-25 Component Architecture for Object Relational DBMSs

18-26 Typical User-Defined Types  Audio  Video  Text  Image  Spatial  Time series  XML

18-27 Other Object Features  Subtable families  Reference and row data types  Nested tables

18-28 Object-Oriented DBMS  A new kind of DBMS designed especially for objects.  Object-oriented DBMSs have an object query processor and an object kernel.  The Object Data Management Group (ODMG) provides the standard for object- oriented DBMSs.

18-29 Component Architecture for Object-Oriented DBMSs

18-30 Summary of Architectures  Market niche for each architecture  Simpler architectures less popular over time  Object database middleware coexist with other approaches  Object-relational approach dominates object-oriented approach

18-31 SQL:2003 Object Features  Very large standard  Core language part  Parts and packages for non core features  Details about basic and enhanced object support  Two levels of conformance

18-32 SQL:2003 Parts  Core parts (1,2,11): framework, foundation, schemas  Non core parts  Call level interface  Persistent stored modules  Management of external data  Object level bindings  XML specifications

18-33 SQL:2003 Packages  Enhanced data-time facilities  Enhanced integrity management  Basic object support  Enhanced object support  Active databases  OLAP facilities

18-34 User-Defined Types  Bundles data and procedures  Support definition of structured types, not just extensions of standard types  Use as data types for columns in tables, passed as parameters, and returned as values  User-defined functions can be used in expressions in the SELECT, the WHERE, and the HAVING clauses.

18-35 User-Defined Type Example

18-36 Explicit Methods  Return single values and use input parameters  Implicit first parameter: part of user- defined type  CREATE METHOD statement for method body  Mutation methods: change values  Procedures and functions not associated with types

18-37 Implicit Methods  Automatically exist for all user-defined types  Constructor method: creates an empty instance  Observer methods: retrieve values  Mutation methods: change values

18-38 User-Defined Type Using an Array Example 2: Triangle type using an ARRAY CREATE TYPE Triangle AS ( Corners Point ARRAY[3], Color INTEGER ) METHOD Area() RETURNS FLOAT, -- Computes the area METHOD Scale (Factor FLOAT) RETURNS Triangle -- Computes a new triangle scaled by factor NOT FINAL;

18-39 User-Defined Type Using a Multiset Example 3: Polygon type using an ARRAY CREATE TYPE Triangle AS ( Corners Point MULTISET, Color INTEGER ) METHOD Area() RETURNS FLOAT, -- Computes the area METHOD Scale (Factor FLOAT) RETURNS Polygon -- Computes a new polygon scaled by factor NOT FINAL;

18-40 Table Definitions  Traditional style: foreign keys to link tables  Typed tables: supports object identifiers and object references  Row type constructor: supports rows as variables and parameters

18-41 Row Type Usage

18-42 User-Defined Type Usage

18-43 Subtable Families  A table can be declared as a subtable of another table.  A subtable inherits the columns of its parent tables.  SQL:2003 limits inheritance for tables to single inheritance.  Set inclusion determines the relationship of a table to its subtables.

18-44 Subtable Example

18-45 Subtable Side Effects  Subtable insert: corresponding row is inserted into each ancestor table.  Parent update: column updated in all direct and indirect subtables  Inherited column update: column is changed in each ancestor table  Deletion: every corresponding row in both parent and subtables is also deleted.

18-46 Manipulating Complex Objects and Subtable Families  Path expressions to manipulate columns with row references.  References to methods in expressions using the dot notation  Testing membership in a specific table without being a member of any subtables.

18-47 Using the ROW Keyword

18-48 Obtaining Object Identifiers

18-49 Path Expression Example

18-50 Oracle 10g Object Features  Supports most parts of the SQL:2003 object packages  User-defined types  Typed tables  Other object features

18-51 User-Defined Type Example

18-52 Inheritance

18-53 Typed Tables

18-54 Inheritance for Typed Tables

18-55 Inserting into Typed Tables

18-56 Path Expressions

18-57 Other Object Features  Type substitutability for subtables  Hierarchical views  Nested tables  XML support

18-58 Type Substitution and Hierarchical Views  Type substitution: row or column can contain type X or subtypes of X  Hierarchical views: views with inheritance  Limitations for managing set inclusion relationships  Must manage storage model for hierarchical views  Difficult to use reference types and subtype columns

18-59 Nested Table Support  Utility of nested tables is not clear for business databases  Oracle 10g features  TABLE and NESTED TABLE constructors  Query results can include nested tables.  Comparison operators for nested tables  Set operators for nested tables  Views with nested tables

18-60 XML Document Support  Part 14 of SQL:2003  Oracle 10g features  XMLType in columns  XML schema support  XML/SQL duality  XML query operators  Optimization with query rewrite

18-61 Summary  Three principles of object-oriented computing guide the development of object DBMSs.  A number of object DBMS architectures are commercially available.  SQL:2003 supports definition and manipulation of object relational databases.  Oracle 10g is a significant implementation of the SQL:2003 object packages