Tài liệu Oracle Unleashed- P1 doc

36 -- Introduction to Oracle Power Objects 37 -- Connecting to Database Sources Through Sessions 38 -- Managing the Database 39 -- Understanding the Application Model 40 -- Objects Withi

2 Oracle and Client/Server

3 Overview of the Oracle Architecture

11 Managing the Database

12 Managing Disk Space

13 Managing Users

14 Backup and Recovery

15 Performance Tuning and Optimizing

36 Introduction to Oracle Power Objects

37 Connecting to Database Sources Through Sessions

38 Managing the Database

39 Understanding the Application Model

40 Objects Within Oracle Power Objects

41 Building an Application with the Form Designer

42 Creating Reports

43 Using the Debugger

44 Oracle Basic

45 Libraries, User-Defined Properties and Methods, and Classes

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Part VIII

46 Introduction to Oracle Objects for OLE

47 Oracle OLE Automation Server

48 The Oracle Data Control

49 Oracle Objects for OLE C++ Class Library

E Oracle Power Objects Programming Reference

Installing the CD-ROM

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■ It's a Database Jim, But Not As We Know It

■ SELECT * FROM book

■ "But I've used Oracle Before"

■ Is this Book for Me?

Oracle™ Unleashed

Oracle™ Unleashed

SAMS Publishing

201 West 103rd Street, Indianapolis, Indiana 46290

Copyright © 1996 by Sams Publishing

FIRST EDITION

All rights reserved No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher No patent liability is assumed with respect to the use of the information contained herein Although every precaution has been taken in the preparation of this book, the publisher and author assume no responsibility for errors or omissions Neither

is any liability assumed for damages resulting from the use of the information contained herein For information, address Sams Publishing, 201 W 103rd St., Indianapolis, IN 46290

All works in chapters 36-48, 54, 56-58 and Appendix E reproduced herein are Copyright [c] Oracle Corporation 1996 All rights reserved All other chapters are Copyright [c] 1995 by Sams Publishing

Oracle Corporation shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the programs or program segments that are included This manual is not a publication of Oracle Corporation, nor was it produced in conjunction with Oracle Corporation

All works in chapters 36-48, 54, 56-58 and Appendix E reproduced herein are Copyright (insert copyright symbol) Oracle Corporation 1996 All rights reserved

ORACLE is a registered trademark of Oracle Corporation, Redwood Shores, California, U.S.A Oracle Power Objects is

a trademark of Oracle Corporation, Redwood Shores, California, U.S.A

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Oracle Corporation shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the programs or program segments that are included This manual is not a publication of Oracle Corporation, nor was it produced in conjunction with Oracle Corporation

All other chapters are Copyright (insert copyright symbol) 1996 by Sams Publishing

All rights reserved No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher No patent liability is assumed with respect to the use of the information contained herein Although every precaution has been taken in the preparation of this book, the publisher and author assume no responsibility for errors or omissions Neither

is any liability assumed for damages resulting from the use of the information contained herein For information, address Sams Publishing, 201 W 103rd St., Indianapolis, IN 46290

International Standard Book Number: 0-672-30872-X

Library of Congress Catalog Card Number: 95-72326

99-98-97-96 -4-3-2-1

Interpretation of the printing code: the rightmost double-digit number is the year of the book's printing; the rightmost single-digit, the number of the book's printing For example, a printing code of 96-1 shows that the first printing of the book occurred in 1996

Printed in the United States of America

All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized Sams Publishing cannot attest to the accuracy of this information Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark

Publisher and President: Richard K Swadley

Acquisitions Manager: Greg Wiegand

Development Manager: Dean Miller

Managing Editor: Cindy Morrow

Marketing Manager: Gregg Bushyeager

Mona Brown, Michael Brumit,

Jeane Clark, Michael Dietsche,

Juudy Everly, Jason Hand,

Michael Henry, Aleta Howard,

Ayanna Lacey, Kevin Laseau,

Cheryl Moore, Casey Price,

Brian-Kent Proffit, Beth Rago

Bobbi Satterfield, Laura A Smith

SA Springer, Josette Starks

Andrew Stone, Susan Van Ness

Mark Walchle, Colleen Williams

3 Overview of the Oracle Architecture

Part II Oracle Tools and Utilities

9 Import and Export

Part III Database Administration

10 Installation

11 Managing the Database

12 Managing Disk Space

13 Managing Users

14 Backup and Recovery

15 Performance Tuning and Optimizing

Part VII Oracle Power Objects

36 Introduction to Oracle Power Objects

37 Connecting to Database Sources Through Sessions

38 Managing the Database

39 Understanding the Application Model

40 Objects Within Oracle Power Objects

41 Building an Application with the Form Designer

42 Creating Reports

43 Using the Debugger

44 Oracle Basic

45 Libraries, User-Defined Properties and Methods, and Classes

Part VIII Oracle Objects for OLE

46 Introduction to Oracle Objects for OLE

47 Oracle OLE Automation Server

48 The Oracle Data Control

49 Oracle Objects for OLE C++ Class Library

Part IX Advanced Topics

55 The Oracle WebSystem and the World Wide Web Interface Kit

Part X Oracle Packages

Michael Richards CEO

Advanced Information Systems Inc

(800) 327-9725

About the Authors

ADVANCED INFORMATION SYSTEMS, Inc Michael Richards is the CEO of Advanced Information Systems

(AIS), Inc AIS is a professional software development and consulting firm that offers a range of products and services specializing in Oracle development A primary objective of AIS is to provide technical solutions in the form of

Management Consulting, Project Staffing, Independent Consultants, and Training Services

AIS offers a popular approach to client/server development called Rapid Application Foundation (RAF) RAF is a set of predeveloped code libraries coupled with skills transfer RAF is offered as a one-or two-week training system that is tailored to develop an in-house application system AIS clients receive a well-crafted client/server system that takes advantage of today's premier development systems including Oracle and Visual Basic Oracle and these tools can be purchased at a discount from AIS AIS can be reached at (800) 327-9725

Rachel Becker is a software consultant who has been developing administrative business applications since 1985 She

has worked primarily with Oracle Tools since 1989, using Oracle's CASE tool since 1991 Her project experience up and down the east coast includes university, insurance, utilities, and medical environments She is currently living in the Charlotte, NC area Reach her via e-mail at wbecker709@aol.com

Matthew Bennett is a Senior Technical Marketing Manager in the Web/Workgroup Systems Division at Oracle

Corporation He is currently responsible for a team of application developers working on creating World Wide Web applications using Oracle's newest Web technologies Before working at Oracle, he was the founder of Data Smiths, a Provo, Utah-based systems integration firm At Data Smiths, he was responsible for publishing articles in Network Computing, Software Development, and numerous technical journals

Winnie In-Kuan Cheang (B.S., M.S., M.B.A.),is currently a Senior Technical Analyst in Oracle Corporation's

Worldwide Support She provides mission-critical support to database administrators and developers of Oracle products

on a wide variety of systems and networks She is also the NetWare administrator and DBA for the Desktop Support Group production system at Oracle Winnie is an ECNE and has many years of computer networking and relational database experience as a programmer, technical analyst, instructor, and consultant She has presented and published papers on relational database applications for the Human Genome Project in the IEEE proceedings

Mike Conklin, an independent consultant working in Rochester, New York, has more than 17 years experience—the

past 6 working with Oracle specific applications Mike and his wife Pam, have enjoyed 21 years of marriage Together, they home-educate their three children, studying along with them By God's grace they have chosen to build their

relationships and values upon Biblical principles Renovating an 1800's farm house where they welcome frequent (and flexible!) guests is an added challenge

Patrick Connors is the CASE analyst for the Arizona Department of Health Services He is responsible for

administering the Designer/2000 tool and acts as a consultant on Oracle CASE projects He has been an Oracle

programmer since 1990 and a computer professional since 1980, working on a variety of projects from accounting systems to video games In his spare time, he is a cartoonist and kayaker Patrick is single and resides in Phoenix

Joe Greene has worked in a variety of fields, from driving submarines to spacecraft design Along the way, he began to

implement computer systems to meet various business needs This has lead to a career as a computer consultant with a number of assignments working with Oracle databases His experience ranges from very large data warehouses (with more than 100 gigabytes of data) to small scientific data collection systems, with a wide variety of databases in between

He is the author of the Oracle DBA Survival Guide, also from Sams Publishing

Scott Hillegas is a senior consultant with Integrated Systems Consulting Group, located in Wayne, Pa He has more than

10 years of Oracle DBA experience and more than 20 years of MIS experience on various platforms His area of

experience is the design, development, and implementation of relational database and client/server technologies, and most notably, Oracle on the UNIX platform He began his Oracle career with version 5.1, building OLTP systems, and today is working with version 7.2, building DSS data warehousing systems

Dan Hotka has 17 years in the computer business, 10 of those with the Oracle products He first worked with Oracle

products in the version 4 days, when SQL*Plus was called UFI (User Friendly Interface) and when Oracle Forms was nothing more than a product called Fastforms, which generated a basic INP file that was compiled with IAG and

interpreted by IAP There was also a neat little report writer called RPT He worked with Oracle (including Oracle Corp)

as a marketing presales support representative (more than four years) and in various consulting, development, and DBA Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.

roles (more than six years) He has written language source code filters that have converted entire applications written in other languages into the Oracle languages These filters include both data and program conversions He has worked extensively with each of the Oracle releases since Oracle 4, including the current Oracle 7.1 release

Steve Hughes has been in data processing for more than 10 years With a strong applications development background

in Xbase languages, primarily using FoxPro with TRO as an application foundation, he has recently turned his

experience and enthusiasm to Oracle Recently promoted to the position of Oracle DBA at CMS Therapies in Charlotte,

NC, his responsibilities include installing and upgrading client/server software, data backup and recovery, user access maintenance, and performance tuning His experience includes Oracle running on Novell NetWare 3.12 and a DEC Alpha running DEC OSF/1 He can be reached via CompuServe at 74133,1327

Dave Kinchen has been involved with Oracle for most of his professional career, spanning development, database

administration, and design on many different platforms On the rare occasions Dave is not working, you might find him with his family doing something fun in the Rockies

Bruce Kostival holds a BSEE degree from The Pennsylvania State University and an MBA in Information Systems

from The University of Colorado Having been in the field of software development for more than 16 years, he has written software in many areas from real-time data acquisitions to Oracle RDBMS database development He has

developed Oracle software in both the VMS and UNIX environments Currently, he is employed with a direct marketing company in private industry as a Senior Programmer/Analyst His real-life interests are his two (going on three) children,

and his lovely and talented wife Ruthann In his little spare time, he enjoys Colorado's fabulous skiing, on- or off-piste!

Ronnie Lashaw has more than 10 years of experience developing and deploying client/server database applications for

clients including the US Air Force, NASA, Veterans Administration, US Dept of Education, Unisys, Boeing, and Lockheed Martin He has a BS in Computer Science and a minor in Industrial Engineering from North Carolina State University He has extensive knowledge of Oracle products with emphasis on Oracle Power Objects His primary

objective is to provide intuitive, visually appealing, user-friendly, graphical client/server applications He can be reached

on CompuServe at 74513,1076 or on the Internet at rlashaw@us.oracle.com for discussions about Power Objects

Kelly Leigh, with more than eight years' experience in the systems administration world made the jump into database

administration over three years ago Starting out with Informix and moving to Oracle, he has had experience in

everything from product installation to database layout to implementing custom applications Currently working for a small company in Longmont, Colorado, he is also co-owner of Colorado Business Solutions, a company created to provide small and mid-range business consulting in a wide range of areas including office automation, network

installation, database installation, and software training Outside of work, Kelly is an avid hiker and camper, spending much of his free time in the foothills of the Rocky mountains

Keith Majkut is a Senior Software Engineer in the Workgroup Solutions Division of Oracle Corporation He has been

with Oracle for five years, and in that time has worked on a variety of products including Oracle Reports, the Oracle Workgroup Server, Oracle Objects for OLE, and currently Personal Oracle7 for Windows 95 Keith grew up in Milford, Connecticut and graduated from Northeastern University of Boston Massachusettes in 1990 with a Bachelor of Science

in Computer Science When he's not working or spending time with his wife Karen, he can be found riding his

motorcycle around the San Francisco Bay area, where he currently resides Keith can also be found roaming the Oracle groups on the Internet and CompuServe, or you can contact him directly at kmajkut@netcom.com or on CompuServe at 74343,1566

Byron Pearce is the Database Administrator for Nokia Mobile Phones U.S.-based operations in Fort Worth, Texas,

where he has the dual capacity as the MIS Operations Supervisor He is responsible for insuring the availability and overall health of all UNIX and Oracle RDBMS Systems that support Nokia's U.S.-based manufacturing and distribution systems Byron has worked in a multi-functional capacity in the MIS Departments for several companies, including SONAT and Tandy Corporation, working as a systems operator, applications developer, systems analyst, project leader,

database administrator, and UNIX system administrator Recently, he completed technical editing of the Oracle DBA Survival Guide by Sams He lives in Arlington, Texas with his wife, Cherie, and can be reached via Internet at

Bpearce163@aol.com

Lave Singh (BSc, ACGI, MBCS), is founder and head of Titanium Computers Ltd, a training and consulting firm,

which over the last eight years has provided Oracle training and consulting services to organizations in Europe, North America, and the Middle East They specialize in DBA, Tuning, Forms 4.5, Short-Term Technical Consulting, as well as running training courses for a number of blue-chip clients More than 13 years ago, Lave began at Imperial College on a Computational Science course and since then has been working in the computing field His wife Permjit and three young children (Benisha, Taejen, and Kashmir) provide a semblance (only just) of sanity away from machines He can be reached on e-mail at 100135.1773@compuserve.com or by phone on +44(181) 692 5204

Vic Stambaugh is a principal and Director of Technology Marketing for Integrated Systems Consulting Group, Inc

(ISCG), a Pennsylvania-based consulting firm that develops and integrates client/server systems for the pharmaceutical, health care, and life sciences industries He has more than 16 years of software development experience, in both full life cycle applications development and database administration, and has worked exclusively with Oracle-based systems since 1986 Vic has designed and taught numerous database and Oracle courses, and is active in the Oracle community

as a frequent presenter at international and regional user conferences He currently serves on the Board of Directors for the Oracle CASE SIG and also served on the Board of Advisors for the Oracle Consultants Alliance

Brian Twidt has been developing client/server database applications for five years His experience includes applications

designed for such clients as Oracle, NASA, FDA, US DOE, Boeing, and Lockheed Martin The majority of his

experience is related to using desktop development tools such as Oracle Power Objects, Microsoft Visual Basic, C++, and Oracle Card He has a BS in Computer Science and a minor in Graphic Communications from North Carolina State University His primary objective is to develop applications that are graphical, intuitive, innovative, and compelling Any comments regarding Oracle Power Objects can be directed to Mr Twidt via the Internet at btwidt@us.oracle.com

Gigi Wadley has been involved with Oracle for approximately five years Her experience has been obtained through

government and private industries The majority of the work she has done consists of Pro*C and SQL*Forms She has been married for 13 years and has a 12-year-old daughter Most of their lives have been spent in Colorado where they enjoy the lifestyle that the state provides

Chester "Chet" West began his computer career nine years ago as a computer operator in the US Air Force He later

cross-trained into the computer programming career field where he developed and maintained real-time communications system software at both Offutt AFB and Tinker AFB There he gained his first exposure to database programming, though home-grown He also began development of an office configuration management system using FoxPro as his database engine Upon completion of his BS in Computer Science, he went to work for Threads USA in Gastonia, NC, where he helped develop and maintain FoxPro applications From there, he became a consultant for The Registry and was contracted by CMS Therapies, where he developed both FoxPro and Oracle systems He is the senior programmer, leading all new Oracle development and assisting in the maintenance of legacy FoxPro systems He can be reached by sending e-mail to 102046,517@compuserve.com

Kevin Whitley has worked on everything from mainframe Fortran to micro assembler over the last 15 years He is

currently a lead architect at BBN Domain and uses C++ to develop client/server applications for the pharmaceutical and manufacturing industries

Joe Zafian III has been working full-time in Information Systems since graduation from New Jersey Institute of

Technology with a B.S in Computer Science in 1981 Currently a consultant specializing in Oracle database

applications, he has been working with all versions of the RDBMS and its associated tools since 1986 As a consultant,

he has worked with a number of Fortune 500 clients in several industries across a vast array of hardware platforms This experience qualified him to speak at the international Oracle Users' Week Conference in 1994 (Predicting Storage Requirements for Large, Dynamic Oracle Databases and Advanced Techniques for Dynamic, User-Driven Applications

in SQL*Forms 3.0) and 1995 (Quality Assurance for Oracle Projects and Advanced Techniques for Oracle Forms 4.5 Applications) When not striving to deliver quality Oracle systems (or writing about it), Joe enjoys sports, fishing and other outdoor activities with his wife, Ruth He can be contacted via CompuServe at 73744,2713

Ken Zimmerman received his Bachelor of Science in Geology from Duke University in 1982 However, his interest in

computers dates back as far as 1975 when he became intrigued with what was then that era's "information highway," available through his preparatory school's newly acquired Digital PDP-11/70 system His work with computers, and Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.

especially with database management systems, continued through his undergraduate years as well as during his graduate work in Petrology as an ARCO fellow at USC In 1985, Ken founded Chateaux Software Development, Inc., a company specializing in PowerBuilder, Oracle, Lotus Notes, and Progress solutions on UNIX, VMS, MS-Windows, Windows-NT Advanced Server, and Novel platforms His company's primary goal has been to develop high-performance applications

on a variety of platforms, ranging from low-end 80x86-based DOS and UNIX systems to midrange HP-9000 HP/UX, IBM AIX, and DEC VAX systems His firm's strengths are especially geared toward producing highly efficient systems, primarily by developing compact code, will-designed data structures, and a user-oriented architecture Chateaux is building on these strengths and provides enterprise-quality solutions to WWW/RDBMS integration problems Ken Zimmerman and Chateaux can be reached at 9 Tierney Lane, Greens Farms CT 06436, by phone at (203) 259-9665, and through CompuServe at 74404,1401

Introduction

When I first started using Oracle many years ago, it was possible to know the database and the tools available With the

rash of recent releases of different options for the database and the spate of new tools, only people who wear their underpants over their trousers will be able to know everything there is to know about the Oracle products If you were an experienced Oracle developer three years ago and since then have been locked away—not able to see the new Oracle versions of the database and tools—there will be very little that you will recognize today Along with changes in other computing technologies, the rate of change with Oracle is constantly increasing, which is all the more interesting for us who get turned on by the software You'll get a running start with the pages that follow

Oracle Unleashed is one of the most comprehensive books on Oracle and its tools available today It's written by authors

who have real-life experience using the Oracle tools (most of whom are members of the Oracle Business Alliance Program) We will show you what's important, the pitfalls, tips from real-life experiences, and code examples—The kind

of information that can give you the cumulative experience of many years of expertise

It's a Database Jim, But Not As We Know It

Oracle Corporation, headquartered in Redwood Shores, California, was best known for being a database company that also provided its own tools for working with the database Many sites used the power of the Oracle database but used better third-party tools as their interface to the database

Today, the Oracle tools are among the best and most powerful development tools available; if you want it, Oracle can do

it Oracle now provides the database, multiple choices of tools, and utilities to connect to the Oracle database from party products, applications (the best known of which is Financials), and a host of other products In the next year Oracle will release an Internet machine, making the scope of Oracle products mushroom Not just a database provider but a tools company, software house writing applications, hardware manufacturer, and Internet service provider? (Just give them time.)

third-SELECT * FROM book

The beginning of the book lays the foundation on top of which all the tools will be built—the architecture of the database and the two languages used in most tools, SQL and PL/SQL If you don't (yet) want to know how the electricity works but just want to switch on the light, skip over the architecture section

For database administrators and others who need to know how to keep the database humming, the database

administration section will detail the most common functions of looking after the database and traps to watch out for The remaining sections look at the tools of most interest to developers

But how is Oracle going to be useful in producing your system? It gives you a multitude of choices to work with; in fact,

at times it seems like too many choices You have choices with the database itself about which database options you want to use There are choices about which Oracle tools to use: Forms, Reports, Graphics, Power Objects, and more If you don't want to use the Oracle tools, you can connect PowerBuilder, SQLWindows, Visual Basic, Delphi, and other

third-party tools You can even use the Oracle tools with non-Oracle data sources using ODBC, User Exits written in third-generation languages, or the gateway database products Whatever you want to do, you can do it in one way or another Choices, choices, and even more choices

In addition to using the database and tools, you'll want to manage the development life cycle right from the strategy stage through to implementation and maintenance What better tool to use than the Designer/2000 product You can even generate your programs from this tool Check out the Designer/2000 and Developing Applications sections of the book for designing and developing applications using Designer/2000

Today, for any application development project, making the right selection of tools and database is even harder and more important Pick the wrong options, and the time and effort needed can be vastly increased The information available in this book will make sifting through the plethora of choices easier

"But I've used Oracle Before"

If you've used previous versions of Oracle products, you'll find it easier to get a grip on the pertinent points of the new tools and components, and to add more background to areas such as the architecture, database administration,

Designer/2000, and the other tool options available If you already have experience with the newer products, then

discover how the authors are using the newest tools and options now available

Is this Book for Me?

Now you know what's going to be covered in the book, the next question you'll probably be asking is whether it's the right book for me

This book is aimed at

● Experienced Oracle Developers

● Database administrators

● Intermediate developers, especially those who have used previous versions of the products

● Those who have used similar technologies and want to quickly get a grip on Oracle and its tools

● Technical managers who want to know about the available options

The book covers SQL and PL/SQL in enough detail to allow you to get up and running quickly with developing with Oracle Because it is geared toward an intermediate to advanced audience, however, this book quickly covers the

essential basics of these two languages and shows you how to start producing real-life applications

Take a while to play around with the products while you're reading the book Look at the examples, try them out, and explore You'll gain a far deeper understanding by using the products while reading

Open your mind, open the book, and get ready to unleash the power of Oracle!

Advanced Information Systems (AIS), Inc

Michael Richards, CEO

Joe Zafian, III

Not pictured: Kelly Leigh, Gigi Wadley, Kevin Whitley, and Kenneth Zimmerman

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● 1

❍ What Is an RDBMS?

■ The Relational Database Model

■ Hierarchical and Network Models

■ Elements of the Relational Model

■ Relational Data Structures

■ Key Values and Referential Integrity

■ Relational Algebra

■ RDBMS Components

■ The RDBMS Kernel

■ The Data Dictionary

■ Nonprocedural Data Access (SQL)

meaningful information systems The evolution of high-powered database engines such as Oracle7 has fostered the development of advanced "enabling" technologies including client/server, data warehousing, and online analytical processing, all of which comprise the core of today's state-of-the-art information management systems

Examine the components of the term relational database management system First, a database is an integrated

collection of related data Given a specific data item, the structure of a database facilitates the access to data related to it,

such as a student and all of his registered courses or an employee and his dependents Next, a relational database is a type of database based in the relational model; non-relational databases commonly use a hierarchical, network, or object- oriented model as their basis Finally, a relational database management system is the software that manages a relational

database These systems come in several varieties, ranging from single-user desktop systems to full-featured, global, enterprise-wide systems, such as Oracle7

This chapter discusses the basic elements of a relational database management system, the relational database, and the software systems that manage it Also included is a discussion of nonprocedural data access If you are a new user to relational database technology, you'll have to change your thinking somewhat when it comes to referencing data

nonprocedurally

The Relational Database Model

Most of the database management systems used by commercial applications today are based on one of three basic models: the hierarchical model, the network model, or the relational model The following sections describe the various Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.

differences and similarities of the models

Hierarchical and Network Models

The first commercially available database management systems were of the CODASYL type, and many of them are still

in use with mainframe-based, COBOL applications Both network and hierarchical databases are quite complex in that

they rely on the use of permanent internal pointers to relate records to each other For example, in an accounts payable

application, a vendor record might contain a physical pointer in its record structure that points to purchase order records Each purchase order record in turn contains pointers to purchase order line item records

The process of inserting, updating, and deleting records using these types of databases requires synchronization of the pointers, a task that must be performed by the application As you might imagine, this pointer maintenance requires a significant amount of application code (usually written in COBOL) that at times can be quite cumbersome

Elements of the Relational Model

Relational databases rely on the actual attribute values as opposed to internal pointers to link records Instead of using an internal pointer from the vendor record to purchase order records, you would link the purchase order record to the vendor record using a common attribute from each record, such as the vendor identification number

Although the concepts of academic theory underlying the relational model are somewhat complex, you should be

familiar with are some basic concepts and terminology Essentially, there are three basic components of the relational model: relational data structures, constraints that govern the organization of the data structures, and operations that are performed on the data structures

Relational Data Structures

The relational model supports a single, "logical" structure called a relation, a two-dimensional data structure commonly called a table in the "physical" database Attributes represent the atomic data elements that are related by the relation For

example, the Customer relation might contain such attributes about a customer as the customer number, customer name, region, credit status, and so on

In relational database design literature, you might see a relation denoted as Relation(attribute1, attribute2, )

with the name of the relation followed by the attribute list enclosed in parentheses

Customer(Customer_ID, Customer_Name, Region, )

The actual data values for the attributes of a relation are stored in tuples, or rows, of the table It is not necessary for a

relation to have rows in order to be a relation; even if no data exists for the relation, the relation remains defined with its set of attributes Figure 1.1 illustrates the basic elements of the Customer relation

Figure 1.1 The basic components of a relation

Key Values and Referential Integrity

Attributes are grouped with other attributes based on their dependency on a primary key value A primary key is an

attribute or group of attributes that uniquely identifies a row in a table A table has only one primary key, and as a rule, every table has one Because primary key values are used as identifiers, they cannot be null Using the conventional

notation for relations (shown in the note), an attribute is underlined to indicate that it is the primary key of the relation If

a primary key consists of several attributes, each attribute is underlined

You can have additional attributes in a relation with values that you define as unique to the relation Unlike primary

keys, unique keys can contain null values In practice, unique keys are used to prevent duplication in the table rather than identify rows Consider a relation that contains the attribute, United States Social Security Number (SSN) In some rows, this attribute may be null in since not every person has a SSN; however for a row that contains a non-null value for the SSN attribute, the value must be unique to the relation

Linking one relation to another typically involves an attribute that is common to both relations The common attributes

are usually a primary key from one table and a foreign key from the other Referential integrity rules dictate that foreign

key values in one relation reference the primary key values in another relation Foreign keys might also reference the primary key of the same relation Figure 1.2 illustrates two foreign key relationships

Figure 1.2 Foreign keys that reference a primary key in another table as well as a primary key in the same table

Many database design tools use underlines to denote primary keys in diagram and report views Depending on the tool that you use, you might also see (PK) and (FK) next to attributes to denote primary and foreign keys,

respectively

You will notice frequent references to the DEPT and EMP sample tables throughout Oracle documentation You can find these tables along with other sample database objects in Oracle's standard demonstration account You usually access the account with the username/password combination scott/tiger

You typically design a relational database using the rules of normalization that dictate which attributes belong in which

relations There are five levels (or forms) of normalization to which a data model can comply Of the five, most database

designs minimally conform to the third normal form This form serves to alleviate redundancy in the data model,

requiring each atomic data element to appear once in the data model and be dependent on one and only one primary key Employing a normalized data model protects against insert, update, and delete anomalies that can arise as a result of incorrectly defined relations

Table 1.1 Algebra operations of the relational model.

Operation Type Resulting Relation

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Union Binary Rows from the two relations are combined, eliminating duplicate rows.

Intersection Binary Rows common to two relations

Difference Binary Rows that exist in the first relation but not in the second

Projection Unary Rows that contain some of the columns from the source relation

Selection Unary Rows from the source relation that meet query criteria

Product Binary Concatenation of every row in one relation with every row in another

Concatenation of rows from one relation and related rows from another

The source relations used by UNION, INTERSECTION, and DIFFERENCE must have attribute lists that match

in number and data type

RDBMS Components

Two important pieces of an RDBMS architecture are the kernel, which is the software, and the data dictionary, which

consists of the system-level data structures used by the kernel to manage the database

The RDBMS Kernel

You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data Like an operating system, Oracle7 manages and controls access to a given set of resources for concurrent database users The subsystems of an RDBMS closely resemble those of a host operating system and tightly integrate with the host's services for machine-level access to resources such

as memory, CPU, devices, and file structures An RDBMS such as Oracle7 maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage;

dispatches and schedules user requests; and manages space usage within its tablespace structures Figure 1.3 illustrates the primary subsystems of the Oracle7 kernel that manage the database

Figure 1.3 An RDBMS and its multiple subsystems

The Data Dictionary

A fundamental difference between an RDBMS and other database and file systems is in the way that they access data A RDBMS enables you to reference physical data in a more abstract, logical fashion, providing ease and flexibility in developing application code Programs using an RDBMS access data through a database engine, creating independence from the actual data source and insulating applications from the details of the underlying physical data structures Rather than accessing a customer number as bytes 1 through 10 of the customer record, an application simply refers to the attribute Customer Number The RDBMS takes care of where the field is stored in the database Consider the amount of

programming modifications that you must make if you change a record structure in a file system-based application For example, if you move the customer number from bytes 1 through 10 to bytes 11 through 20 to accommodate an

additional field, all the programs that use the customer number would require modification However, using an RDBMS, the application code would continue to reference the attribute by name rather than by record position, alleviating the need for any modifications

This data independence is possible because of the RDBMS's data dictionary The data dictionary stores meta-data (data about data) for all the objects that reside in the database Oracle7's data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the Oracle7 kernel As shown in Figure 1.4, requests to read or update the database are processed by the Oracle7 kernel using the information in the data dictionary The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location

Figure 1.4 Access to application data through the Oracle7 Kernel and Data Dictionary

Not only does the RDBMS take care of locating data, it also determines an optimal access path to store or retrieve the data Oracle7 uses sophisticated algorithms that enable you to retrieve information either for the best response for the first set of rows, or for total throughput of all rows to be retrieved

Nonprocedural Data Access (SQL)

An RDBMS differentiates itself with its capability to process a set of data; other file systems and database models process data in a record-by-record fashion You communicate with an RDBMS using Structured Query Language (SQL, pronounced sequel) SQL is a nonprocedural language that is designed specifically for data access operations on

normalized relational database structures The primary difference between SQL and other conventional programming

languages is that SQL statements specify what data operations should be performed rather than how to perform them

For example, consider a procedure to give a salary increase to a particular department for each employee who had not received a raise within the past six months The code segments in Figure 1.5 illustrate the solution to the problem using both procedural and nonprocedural methods

Figure 1.5 SQL programming versus traditional procedural programming methods

Although the example in Figure 5.1 illustrates a simplistic scenario, consider a more complex application and the amount

of programming that is alleviated by using SQL for data access By reducing the amount of programming required for data access, the costs to develop and maintain the data access portions of an application are also reduced

Summary

This chapter describes two aspects of a relational database management system: the relational database model and the database management system The relational model defines relations, which are the underlying database structures; constraints, which are the rules that govern their relationships to one another; and the relational algebra operations that you can perform on relations Relational database management systems work on sets of data and employ many of the concepts of basic set theory

A full-featured management system for a relational database is a sophisticated, complex piece of software that functions very much like an operating system One of the reasons that Oracle has been so successful and widely used is that it has been able to implement the same "logical" database operating system on a variety of host operating systems User access

to objects in the database is controlled by the RDBMS kernel and the meta-data stored in the data dictionary

Applications never access the data in the actual operating system data files directly; instead, all access is provided through the RDBMS

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Access to RDBMS data is accomplished through nonprocedural requests using SQL Compared to conventional file system access, SQL provides "set-at-a-time" as opposed to "row-by-row" processing The language elements and usage

of SQL are covered in Chapter 4

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