Databases A Beginner's Guide

  Databases:

A฀Beginner’s฀Guide About the Author

Andrew฀J.฀(Andy)฀Oppel฀is฀a฀proud฀graduate฀of฀The฀Boys’฀Latin฀School฀of฀Maryland฀and฀of฀

  Transylvania฀University฀(Lexington,฀Kentucky)฀where฀he฀earned฀a฀BA฀in฀computer฀science฀ in฀1974.฀Since฀then,฀he฀has฀been฀continuously฀employed฀in฀a฀wide฀variety฀of฀information฀ technology฀positions,฀including฀programmer,฀programmer/analyst,฀systems฀architect,฀project฀ manager,฀senior฀database฀administrator,฀database฀group฀manager,฀consultant,฀database฀ designer,฀data฀modeler,฀and฀data฀architect.฀In฀addition,฀he฀has฀served฀as฀a฀part-time฀instructor฀ with฀the฀University฀of฀California,฀Berkeley,฀Extension฀for฀more฀than฀20฀years฀and฀received฀ the฀Honored฀Instructor฀Award฀for฀the฀year฀2000.฀His฀teaching฀work฀included฀developing฀three฀ courses฀for฀UC฀Extension,฀“Concepts฀of฀Database฀Management฀Systems,”฀“Introduction฀to฀ Relational฀Database฀Management฀Systems,”฀and฀“Data฀Modeling฀and฀Database฀Design.”฀He฀ also฀earned฀his฀Oracle฀9i฀Database฀Associate฀certification฀in฀2003.฀He฀is฀currently฀employed฀ as฀a฀senior฀data฀modeler฀for฀Blue฀Shield฀of฀California.฀In฀addition฀to฀computer฀systems,฀Andy฀ enjoys฀music฀(guitar฀and฀vocals),฀amateur฀radio฀(Pacific฀Division฀Vice฀Director,฀American฀ Radio฀Relay฀League),฀and฀soccer฀(Referee฀Instructor,฀U.S.฀Soccer).

  Andy฀has฀designed฀and฀implemented฀hundreds฀of฀databases฀for฀a฀wide฀range฀of฀ applications,฀including฀medical฀research,฀banking,฀insurance,฀apparel฀manufacturing,฀ telecommunications,฀wireless฀communications,฀and฀human฀resources.฀He฀is฀the฀author฀ of฀Databases฀Demystified฀(McGraw-Hill฀Professional,฀2004)฀and฀SQL฀Demystified฀ (McGraw-Hill฀Professional,฀2005),฀and฀is฀co-author฀of฀SQL:฀A฀Beginner’s฀Guide฀ (McGraw-Hill฀Professional,฀2009).฀His฀database฀product฀experience฀includes฀IMS,฀DB2,฀ Sybase฀ASE,฀Microsoft฀SQL฀Server,฀Microsoft฀Access,฀MySQL,฀and฀Oracle฀(versions฀7,฀ 8,฀8i,฀9i,฀and฀10g).

  If฀you฀have฀any฀comments,฀please฀contact฀Andy฀at฀andy@andyoppel.com.

  About the Technical Editor

Todd฀Meister฀has฀been฀developing฀using฀Microsoft฀technologies฀for฀more฀than฀ten฀years.฀

  He’s฀been฀a฀Technical฀Editor฀on฀more฀than฀50฀books฀with฀topics฀ranging฀from฀SQL฀Server฀ to฀the฀.NET฀Framework.฀In฀addition฀to฀technical฀editing,฀he฀serves฀as฀an฀Assistant฀Director฀ for฀Computing฀Services฀at฀Ball฀State฀University฀in฀Muncie,฀Indiana.฀He฀lives฀in฀central฀ Indiana฀with฀his฀wife,฀Kimberly,฀and฀their฀four฀incredible฀children.฀Contact฀Todd฀at฀฀ tmeister@sycamoresolutions.com.

  Databases:

A฀Beginner’s฀Guide

Andrew฀J.฀Oppel

  New฀York฀฀฀Chicago฀฀฀San฀Francisco฀฀฀฀ Lisbon฀฀฀London฀฀฀Madrid฀฀฀Mexico฀City฀฀฀฀ Milan฀฀฀New฀Delhi฀฀฀San฀Juan฀฀฀฀ Seoul฀฀฀Singapore฀฀฀Sydney฀฀฀Toronto

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v

Contents

  

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  ฀ Contents฀ ix

  ฀ x ฀ Databases:฀A฀Beginner’s฀Guide

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  Acknowledgments

  any฀people฀were฀involved฀in฀the฀development฀of฀Databases:฀A฀Beginner’s฀Guide—฀ ฀many฀of฀whom฀I฀do฀not฀know฀by฀name.฀First,฀the฀editors฀and฀staff฀at฀McGraw-Hill฀฀

M

  provided฀untold฀hours฀of฀support฀for฀this฀project.฀I฀wish฀to฀especially฀thank฀Editorial฀ Director฀Wendy฀Rinaldi฀as฀the฀individual฀who฀has฀provided฀the฀most฀advice฀and฀inspiration฀ throughout฀the฀development฀of฀all฀my฀books.฀In฀fact,฀it฀was฀Wendy฀who฀got฀me฀started฀as฀a฀ McGraw-Hill฀author.฀I฀also฀wish฀to฀thank฀Lisa฀Theobald฀for฀her฀excellent฀copy฀editing฀and฀ all฀the฀other฀editors,฀proofreaders,฀indexers,฀designers,฀illustrators,฀and฀other฀participants.฀ My฀special฀thanks฀go฀to฀Todd฀Meister,฀the฀technical฀editor,฀for฀his฀attention฀to฀detail฀and฀ his฀helpful฀inputs฀throughout฀the฀editing฀process.฀Finally,฀my฀thanks฀to฀my฀family฀for฀their฀ support฀and฀understanding฀as฀I฀fit฀the฀writing฀schedule฀into฀an฀already฀overly฀busy฀life.

  xi

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  Introduction

  hirty-five฀years฀ago,฀databases฀were฀found฀only฀in฀special฀research฀laboratories,฀ where฀computer฀scientists฀struggled฀with฀ways฀to฀make฀them฀efficient฀and฀useful,฀

T

  publishing฀their฀findings฀in฀countless฀research฀papers.฀Today฀databases฀are฀a฀ubiquitous฀ part฀of฀the฀information฀technology฀(IT)฀industry฀and฀business฀in฀general.฀We฀directly฀and฀ indirectly฀use฀databases฀every฀day—banking฀transactions,฀travel฀reservations,฀employment฀ relationships,฀website฀searches,฀online฀and฀offline฀purchases,฀and฀most฀other฀transactions฀ are฀recorded฀in฀and฀served฀by฀databases.

  As฀is฀the฀case฀with฀many฀fast-growing฀technologies,฀industry฀standards฀have฀lagged฀ behind฀in฀the฀development฀of฀database฀technology,฀resulting฀in฀myriad฀commercial฀ products,฀each฀following฀a฀particular฀software฀vendor’s฀vision.฀Moreover,฀a฀number฀ of฀different฀database฀models฀have฀emerged,฀with฀the฀relational฀model฀being฀the฀most฀ prevalent.฀Databases:฀A฀Beginner’s฀Guide฀examines฀all฀of฀the฀major฀database฀models,฀ including฀hierarchical,฀network,฀relational,฀object-oriented,฀and฀object-relational.฀This฀ book฀concentrates฀heavily฀on฀the฀relational฀and฀object-relational฀models,฀however,฀ because฀these฀are฀the฀mainstream฀of฀the฀IT฀industry฀and฀will฀likely฀remain฀so฀in฀the฀ foreseeable฀future.

  The฀most฀significant฀challenge฀in฀implementing฀a฀database฀is฀correctly฀designing฀the฀ structure฀of฀the฀database.฀Without฀a฀thorough฀understanding฀of฀the฀problem฀the฀database฀is฀ intended฀to฀solve,฀and฀without฀knowledge฀of฀the฀best฀practices฀for฀organizing฀the฀required฀ data,฀the฀implemented฀database฀becomes฀an฀unwieldy฀beast฀that฀requires฀constant฀attention.฀

  xiii

  ฀ xiv ฀ Databases:฀A฀Beginner’s฀Guide Databases:฀A฀Beginner’s฀Guide ฀focuses฀on฀the฀transformation฀of฀requirements฀into฀a฀

  working฀data฀model฀with฀special฀emphasis฀on฀a฀process฀called฀normalization,฀which฀ has฀proven฀to฀be฀an฀effective฀technique฀for฀designing฀relational฀databases.฀In฀fact,฀ normalization฀can฀be฀applied฀successfully฀to฀other฀database฀models.฀And,฀in฀keeping฀ with฀the฀notion฀that฀you฀cannot฀design฀an฀automobile฀if฀you฀have฀never฀driven฀one,฀the฀ Structured฀Query฀Language฀(SQL)฀is฀introduced฀so฀that฀the฀reader฀may฀“drive”฀a฀database฀ before฀delving฀into฀the฀details฀of฀designing฀one.

  I’ve฀drawn฀on฀my฀extensive฀experience฀as฀a฀database฀designer,฀administrator,฀and฀ instructor฀to฀provide฀you฀with฀this฀self-help฀guide฀to฀the฀fascinating฀and฀complex฀world฀ of฀database฀technology.฀Examples฀are฀included฀using฀both฀Microsoft฀Access฀and฀Oracle.฀ Publicly฀available฀sample฀databases฀supplied฀by฀these฀vendors฀(the฀Microsoft฀Access฀ Northwind฀database฀and฀the฀Oracle฀Human฀Resources฀database฀schema)฀are฀used฀in฀example฀ figures฀whenever฀possible฀so฀that฀you฀can฀try฀the฀examples฀directly฀on฀your฀own฀computer฀ system.฀A฀self฀test฀is฀provided฀at฀the฀end฀of฀each฀chapter฀to฀help฀reinforce฀your฀learning.

  Who Should Read This Book Databases:฀A฀Beginner’s฀Guide ฀is฀recommended฀for฀anyone฀trying฀to฀build฀a฀foundation฀

  in฀database฀design฀and฀management,฀whether฀for฀personal฀or฀professional฀use.฀The฀book฀ is฀designed฀specifically฀for฀those฀who฀are฀new฀or฀relatively฀new฀to฀database฀technology;฀ however,฀those฀of฀you฀who฀need฀a฀refresher฀in฀normalization฀and฀database฀design฀ and฀management฀will฀also฀find฀this฀book฀beneficial.฀Whether฀you’re฀an฀experienced฀ developer,฀you’ve฀had฀some฀development฀experience,฀you’re฀a฀database฀administrator,฀or฀ you’re฀new฀to฀programming฀and฀databases,฀Databases:฀A฀Beginner’s฀Guide฀provides฀a฀ strong฀foundation฀that฀will฀be฀useful฀to฀any฀of฀you฀wanting฀to฀learn฀more฀about฀database฀ technology.฀In฀fact,฀any฀of฀the฀following฀individuals฀will฀find฀this฀book฀helpful฀when฀ trying฀to฀understand฀and฀use฀databases:

  ●

  ฀ The฀novice฀new฀to฀database฀design฀and฀SQL฀programming

  ●

  ฀ The฀analyst฀or฀manager฀who฀wants฀a฀better฀understanding฀of฀฀how฀to฀design,฀ implement,฀and฀access฀databases

  ●

  ฀ The฀database฀administrator฀who฀wants฀to฀learn฀more฀about฀database฀design

  ●

  ฀ The฀technical฀support฀professional฀or฀testing/QA฀engineer฀who฀must฀perform฀ad฀hoc฀ queries฀against฀SQL฀databases

  ●

  ฀ The฀web฀developer฀writing฀applications฀that฀require฀databases฀for฀data฀persistence

  ฀ Introduction฀ xv

  ●

  ฀ The฀third-generation฀language฀(3GL)฀programmer฀embedding฀SQL฀within฀an฀ application’s฀source฀code

  ●

  ฀ Any฀other฀individual฀who฀wants฀to฀learn฀how฀to฀design฀databases฀and฀write฀SQL฀code฀ to฀create฀and฀access฀databases฀within฀an฀RDBMS No฀matter฀which฀category฀you฀fit฀into,฀you฀must฀remember฀that฀the฀book฀is฀geared฀ toward฀anyone฀wanting฀to฀learn฀standard฀database฀design฀techniques฀that฀work฀on฀any฀ database,฀not฀one฀specific฀vendor’s฀product.฀This฀lets฀you฀apply฀the฀skills฀you฀learn฀in฀ this฀book฀to฀real-world฀situations,฀without฀being฀limited฀to฀product฀standards.฀You฀will,฀ of฀course,฀still฀need฀to฀be฀aware฀of฀how฀the฀product฀you฀work฀on฀implements฀databases,฀ particularly฀dialects฀of฀SQL,฀but฀with฀the฀foundation฀provided฀in฀these฀pages,฀you’ll฀ be฀able฀to฀move฀from฀one฀RDBMS฀to฀the฀next฀and฀still฀have฀a฀solid฀understanding฀of฀ database฀design฀theory.฀As฀a฀result,฀you’ll฀find฀that฀this฀book฀is฀a฀useful฀tool฀to฀anyone฀ new฀to฀databases,฀particularly฀relational฀databases,฀regardless฀of฀the฀product฀used.฀You฀ will฀easily฀be฀able฀to฀adapt฀your฀knowledge฀to฀the฀specific฀RDBMS.

  What the Book Covers Databases:฀A฀Beginner’s฀Guide ฀is฀divided฀into฀three฀parts.฀Part฀I฀introduces฀you฀to฀basic฀

  database฀concepts฀and฀explains฀how฀to฀create฀and฀access฀objects฀within฀your฀database฀ using฀SQL.฀Part฀II฀provides฀you฀with฀a฀foundation฀in฀database฀development,฀including฀ the฀database฀life฀cycle,฀logical฀design฀using฀the฀normalization฀process,฀transforming฀the฀ logical฀design฀into฀a฀physical฀database,฀and฀data฀and฀process฀modeling.฀Part฀III฀focuses฀ on฀database฀implementation฀with฀emphasis฀on฀database฀security,฀as฀well฀as฀the฀advanced฀ topics฀of฀databases฀for฀online฀analytical฀processing฀(OLAP)฀and฀integrating฀objects฀and฀

  XML฀documents฀into฀the฀database,฀allowing฀you฀to฀expand฀on฀what฀you฀learned฀in฀Parts฀I฀ and฀II.฀In฀addition฀to฀the฀three฀parts,฀Databases:฀A฀Beginner’s฀Guide฀contains฀appendices฀ that฀include฀answers฀to฀the฀self-test฀questions฀and฀solutions฀to฀the฀Try฀This฀exercises฀that฀ appear฀throughout฀the฀book.

  Content Description

  The฀following฀outline฀describes฀the฀contents฀of฀the฀book฀and฀shows฀how฀the฀book฀is฀ broken฀down฀into฀task-focused฀chapters:

  Part I: Database Concepts Part฀I฀introduces฀you฀to฀basic฀database฀concepts฀and฀explains฀how฀to฀create฀and฀access฀ objects฀within฀your฀database฀using฀SQL. This฀chapter฀introduces฀fundamental฀concepts฀ Chapter฀1:฀Database฀Fundamentals฀

  and฀definitions฀regarding฀databases,฀including฀properties฀common฀to฀databases,฀prevalent฀

  ฀ xvi ฀ Databases:฀A฀Beginner’s฀Guide

  database฀models,฀a฀brief฀history฀of฀databases,฀and฀the฀rationale฀for฀focusing฀on฀the฀ relational฀model.

  This฀chapter฀explores฀

  Chapter฀2:฀Exploring฀Relational฀Database฀Components฀

  the฀conceptual,฀logical,฀and฀physical฀components฀that฀make฀up฀the฀relational฀model.฀

  Conceptual฀database฀design ฀involves฀studying฀and฀modeling฀the฀data฀in฀a฀technology-

  independent฀manner.฀Logical฀database฀design฀is฀the฀process฀of฀translating,฀or฀mapping,฀ the฀conceptual฀design฀into฀a฀logical฀design฀that฀fits฀the฀chosen฀database฀model฀(relational,฀ object-oriented,฀object-relational,฀and฀so฀on).฀The฀final฀design฀step฀is฀physical฀database฀

  design, ฀which฀involves฀mapping฀the฀logical฀design฀to฀one฀or฀more฀physical฀designs—each฀

  tailored฀to฀the฀particular฀DBMS฀that฀will฀manage฀the฀database฀and฀the฀particular฀computer฀ system฀on฀which฀the฀database฀will฀run.

  This฀chapter฀provides฀an฀overview฀

  Chapter฀3:฀Forms-based฀Database฀Queries฀

  of฀forming฀and฀running฀database฀queries฀using฀the฀forms-based฀query฀tool฀in฀Microsoft฀ Access,฀providing฀a฀foundation฀in฀database฀query฀concepts฀for฀the฀database฀design฀theory฀ that฀follows฀in฀later฀chapters.

  This฀chapter฀introduces฀SQL,฀which฀has฀become฀

  Chapter฀4:฀Introduction฀to฀SQL฀

  the฀universal฀language฀for฀relational฀databases฀that฀nearly฀every฀DBMS฀in฀modern฀use฀ supports.฀The฀reason฀for฀its฀wide฀acceptance฀is฀clearly฀the฀time฀and฀effort฀that฀went฀into฀ the฀development฀of฀language฀features฀and฀standards,฀making฀SQL฀highly฀portable฀across฀ different฀RDBMS฀products.

  Part II: Database Development Part฀II฀provides฀you฀with฀a฀foundation฀in฀database฀development,฀including฀the฀database฀

  life฀cycle,฀logical฀design฀using฀the฀normalization฀process,฀transforming฀the฀logical฀design฀ into฀a฀physical฀database,฀and฀data฀and฀process฀modeling.

  This฀chapter฀introduces฀the฀framework฀in฀which฀

  Chapter฀5:฀The฀Database฀Life฀Cycle฀

  database฀design฀takes฀place,฀a฀useful฀precursor฀to฀the฀particulars฀of฀database฀design.฀The฀

  life฀cycle฀ of฀a฀database฀(or฀computer฀system)฀is฀the฀term฀we฀use฀for฀all฀the฀events฀that฀take฀

  place฀between฀the฀time฀we฀first฀recognize฀the฀need฀for฀a฀database,฀continuing฀through฀its฀ development฀and฀deployment,฀and฀finally฀ending฀with฀the฀day฀it฀is฀retired฀from฀service.

  In฀this฀chapter,฀you฀will฀learn฀

  Chapter฀6:฀Database฀Design฀Using฀Normalization฀

  how฀to฀perform฀logical฀database฀design฀using฀a฀process฀called฀normalization.฀In฀terms฀of฀ understanding฀relational฀database฀technology,฀this฀is฀the฀most฀important฀topic฀in฀this฀book,฀ because฀normalization฀teaches฀you฀how฀best฀to฀organize฀your฀data฀into฀tables.

  In฀this฀chapter,฀we฀will฀look฀at฀entity-

  Chapter฀7:฀Data฀and฀Process฀Modeling฀

  relationship฀diagrams฀(ERDs)฀and฀data฀modeling฀in฀more฀detail.฀The฀second฀part฀of฀the฀ chapter฀includes฀a฀high-level฀survey฀of฀process฀design฀concepts฀and฀diagramming฀techniques.

  ฀ Introduction฀ xvii

  Chapter฀8:฀Physical฀Database฀Design฀ This฀chapter฀focuses฀on฀the฀database฀

  designer’s฀physical฀design฀work,฀which฀is฀transforming฀the฀logical฀database฀design฀into฀ one฀or฀more฀physical฀database฀designs.

  Part III: Database Implementation Part฀III฀focuses฀on฀database฀implementation฀with฀emphasis฀on฀database฀security฀as฀well฀as฀

  the฀advanced฀topics฀of฀databases฀for฀online฀analytical฀processing฀(OLAP)฀and฀integrating฀ objects฀and฀Extensible฀Markup฀Language฀(XML)฀documents฀into฀the฀database;฀this฀allows฀ you฀to฀expand฀on฀what฀you฀learned฀in฀Parts฀I฀and฀II.

Chapter฀9:฀Connecting฀Databases฀to฀the฀Outside฀World฀ This฀chapter฀begins฀with฀

  a฀look฀at฀the฀evolution฀of฀database฀deployment฀models,฀meaning฀the฀ways฀that฀databases฀ have฀been฀connected฀with฀the฀database฀users฀and฀the฀other฀computer฀systems฀within฀the฀ enterprise฀computing฀infrastructure฀(the฀internal฀structure฀that฀organizes฀all฀the฀computing฀ resources฀of฀an฀enterprise,฀including฀databases,฀applications,฀computer฀hardware,฀and฀ the฀network).฀The฀chapter฀then฀explores฀the฀methods฀used฀to฀connect฀databases฀to฀ applications฀that฀use฀a฀web฀browser฀as฀the฀primary฀user฀interface,฀which฀is฀the฀way฀many฀ modern฀application฀systems฀are฀constructed.฀It฀concludes฀with฀a฀look฀at฀current฀methods฀ for฀connecting฀databases฀to฀applications,฀namely฀using฀ODBC฀connections฀(for฀most฀ programming฀languages)฀and฀various฀methods฀for฀connecting฀databases฀to฀applications฀ written฀in฀Java฀(a฀commonly฀used฀object-oriented฀language).

  Chapter฀10:฀Database฀Security฀ This฀chapter฀presents฀the฀need฀for฀security,฀the฀

  security฀considerations฀for฀deploying฀database฀servers฀and฀clients฀that฀access฀those฀ servers,฀and฀methods฀for฀implementing฀database฀access฀security,฀concluding฀with฀a฀ discussion฀of฀security฀monitoring฀and฀auditing.

  Chapter฀11:฀Deploying฀Databases฀ This฀chapter฀covers฀some฀considerations฀

  regarding฀the฀development฀of฀applications฀that฀use฀the฀database฀system.฀These฀include฀ cursor฀processing,฀transaction฀management,฀performance฀tuning,฀and฀change฀control.

  Chapter฀12:฀Databases฀for฀Online฀Analytical฀Processing฀ This฀chapter฀presents฀the฀

  concepts฀of฀databases฀for฀analytical฀processing,฀including฀data฀warehouses฀and฀data฀marts,฀ an฀overview฀of฀data฀mining฀and฀other฀data฀analysis฀techniques,฀along฀with฀the฀design฀ variations฀required฀for฀these฀types฀of฀databases.

  Chapter฀13:฀Integrating฀XML฀Documents฀and฀Objects฀into฀Databases฀ This฀ chapter฀explores฀a฀number฀of฀ways฀to฀integrate฀XML฀and฀object฀content฀into฀databases.

  Part IV: Appendices The฀appendices฀include฀answers฀to฀the฀Self฀Test฀questions฀and฀solutions฀to฀the฀Try฀This฀ exercises฀that฀appear฀throughout฀the฀book.

  ฀ xviii ฀ Databases:฀A฀Beginner’s฀Guide Appendix฀A:฀Answers฀to฀Self฀Tests฀ This฀appendix฀provides฀the฀answers฀to฀the฀Self฀ Test฀questions฀listed฀at฀the฀end฀of฀each฀chapter. Appendix฀B:฀Solutions฀to฀the฀Try฀This฀Exercises฀ This฀appendix฀contains฀solutions,฀

  including฀diagrams฀and฀applicable฀SQL฀code,฀for฀the฀Try฀This฀exercises฀that฀appear฀in฀ nearly฀every฀chapter฀of฀the฀book.

  Chapter Content

  As฀you฀can฀see฀from฀the฀outline,฀Databases:฀A฀Beginner’s฀Guide฀is฀organized฀into฀ chapters.฀Each฀chapter฀focuses฀on฀a฀set฀of฀key฀skills฀and฀concepts฀and฀contains฀the฀ background฀information฀you฀need฀to฀understand฀the฀concepts,฀plus฀the฀skills฀required฀ to฀apply฀these฀concepts.฀Each฀chapter฀contains฀additional฀elements฀to฀help฀you฀better฀ understand฀the฀information฀covered฀in฀that฀chapter:

  Ask the Expert

  Each฀chapter฀contains฀one฀or฀two฀Ask฀the฀Expert฀sections฀that฀provide฀information฀on฀ questions฀that฀might฀arise฀regarding฀the฀information฀presented฀in฀the฀chapter.

  Self Test

  Each฀chapter฀ends฀with฀a฀Self฀Test,฀a฀set฀of฀questions฀that฀test฀you฀on฀the฀information฀and฀ skills฀you฀learned฀in฀that฀chapter.฀The฀answers฀to฀the฀Self฀Tests฀are฀included฀in฀Appendix฀A.

  Try This Exercises

  Most฀chapters฀contain฀one฀or฀two฀Try฀This฀exercises฀that฀allow฀you฀to฀apply฀the฀information฀ that฀you฀learned฀in฀the฀chapter.฀Each฀exercise฀is฀broken฀down฀into฀steps฀that฀walk฀you฀ through฀the฀process฀of฀completing฀a฀particular฀task.฀Where฀applicable,฀the฀exercises฀include฀

  

  related฀files฀that฀you฀can฀download฀from฀our฀website฀at Click฀ Computing฀and฀then฀click฀the฀Downloads฀Section฀link฀on฀the฀left฀side฀of฀the฀page.฀On฀the฀ downloads฀page,฀scroll฀down฀to฀the฀listing฀for฀this฀book฀and฀select฀the฀files฀you฀wish฀to฀ download.฀The฀files฀usually฀include฀the฀SQL฀statements฀or฀diagrams฀used฀within฀the฀Try฀ This฀exercise.

  To฀complete฀many฀of฀the฀Try฀This฀exercises฀in฀this฀book,฀you’ll฀need฀to฀have฀access฀to฀ an฀RDBMS฀that฀allows฀you฀to฀enter฀and฀execute฀SQL฀statements฀interactively.฀If฀you’re฀ accessing฀an฀RDBMS฀over฀a฀network,฀check฀with฀the฀database฀administrator฀to฀make฀sure฀ that฀you’re฀logging฀in฀with฀the฀credentials฀necessary฀to฀create฀a฀database฀and฀schema.฀You฀ might฀need฀special฀permissions฀to฀create฀these฀objects.฀Also฀verify฀whether฀you฀should฀ include฀any฀particular฀parameters฀when฀creating฀the฀database฀(for฀example,฀log฀file฀size),฀ and฀whether฀restrictions฀on฀the฀names฀you฀can฀use฀or฀other฀restrictions฀apply.฀Be฀sure฀to฀ check฀the฀appropriate฀documentation฀before฀working฀with฀any฀database฀product. Part

  

I

Database Concepts

  This page intentionally left blank Chapter

  1 Database Fundamentals

  3

  ฀ 4 ฀ Databases:฀A฀Beginner’s฀Guide Key฀Skills฀&฀Concepts

  ●

  ฀ Properties฀of฀a฀Database

  ●

  ฀ Prevalent฀Database฀Models

  ●

  ฀ A฀Brief฀History฀of฀Databases

  ● Why฀Focus฀on฀Relational?

  ฀ his฀chapter฀introduces฀fundamental฀concepts฀and฀definitions฀regarding฀databases,฀ including฀properties฀common฀to฀databases,฀prevalent฀database฀models,฀a฀brief฀history฀of฀

  T databases,฀and฀the฀rationale฀for฀focusing฀on฀the฀relational฀model.

Properties of a Database

  A฀database฀is฀a฀collection฀of฀interrelated฀data฀items฀that฀are฀managed฀as฀a฀single฀unit.฀This฀ definition฀is฀deliberately฀broad฀because฀so฀much฀variety฀exists฀across฀the฀various฀software฀ vendors฀that฀provide฀database฀systems.฀For฀example,฀Microsoft฀Access฀places฀the฀entire฀ database฀in฀a฀single฀data฀file,฀so฀an฀Access฀database฀can฀be฀defined฀as฀the฀file฀that฀contains฀ the฀data฀items.฀Oracle฀Corporation฀defines฀its฀database฀as฀a฀collection฀of฀physical฀files฀that฀ are฀managed฀by฀an฀instance฀of฀its฀database฀software฀product.฀An฀instance฀is฀a฀copy฀of฀the฀ database฀software฀running฀in฀memory.฀Microsoft฀SQL฀Server฀and฀Sybase฀Adaptive฀Server฀ Enterprise฀(ASE)฀define฀a฀database฀as฀a฀collection฀of฀data฀items฀that฀have฀a฀common฀ owner,฀and฀multiple฀databases฀are฀typically฀managed฀by฀a฀single฀instance฀of฀the฀database฀ management฀software.฀This฀can฀all฀be฀quite฀confusing฀if฀you฀work฀with฀multiple฀products,฀ because,฀for฀example,฀a฀database฀as฀defined฀by฀Microsoft฀SQL฀Server฀or฀Sybase฀ASE฀is฀ exactly฀what฀Oracle฀Corporation฀calls฀a฀schema.

  A฀database฀object฀is฀a฀named฀data฀structure฀that฀is฀stored฀in฀a฀database.฀The฀specific฀ types฀of฀database฀objects฀supported฀in฀a฀database฀vary฀from฀vendor฀to฀vendor฀and฀from฀ one฀database฀model฀to฀another.฀Database฀model฀refers฀to฀the฀way฀in฀which฀a฀database฀ organizes฀its฀data฀to฀pattern฀the฀real฀world.฀The฀most฀common฀database฀models฀are฀ presented฀in฀the฀“Prevalent฀Database฀Models”฀section฀later฀in฀this฀chapter.

  A฀file฀is฀a฀collection฀of฀related฀records฀that฀are฀stored฀as฀a฀single฀unit฀by฀an฀operating฀ system.฀Given฀the฀unfortunately฀similar฀definitions฀of฀files฀and฀databases,฀how฀can฀we฀

  ฀ Chapter฀1:฀ Database฀Fundamentals฀

  5

  make฀a฀distinction?฀A฀number฀of฀Unix฀operating฀system฀vendors฀call฀their฀password฀files฀ “databases,”฀yet฀database฀experts฀will฀quickly฀point฀out฀that,฀in฀fact,฀these฀are฀not฀actually฀ databases.฀Clearly,฀we฀need฀a฀bit฀more฀rigor฀in฀our฀definitions.฀The฀answer฀lies฀in฀an฀ understanding฀of฀certain฀characteristics฀or฀properties฀that฀databases฀possess฀which฀are฀not฀ found฀in฀ordinary฀files,฀including฀the฀following:

  ●

  ฀ Management฀by฀a฀database฀management฀system฀(DBMS)

  ●

  ฀ Layers฀of฀data฀abstraction

  ●

  ฀ Physical฀data฀independence

  ●

  ฀ Logical฀data฀independence These฀properties฀are฀discussed฀in฀the฀following฀subsections.

The Database Management System

  The฀database฀management฀system฀(DBMS)฀is฀software฀provided฀by฀the฀database฀vendor.฀ Software฀products฀such฀as฀Microsoft฀Access,฀Oracle,฀Microsoft฀SQL฀Server,฀Sybase฀ASE,฀ DB2,฀Ingres,฀and฀MySQL฀are฀all฀DBMSs.฀If฀it฀seems฀odd฀to฀you฀that฀the฀DBMS฀acronym฀ is฀used฀instead฀of฀merely฀DMS,฀remember฀that฀the฀term฀database฀was฀originally฀written฀as฀ two฀words,฀and฀by฀convention฀has฀since฀become฀a฀single฀compound฀word.

  The฀DBMS฀provides฀all฀the฀basic฀services฀required฀to฀organize฀and฀maintain฀the฀ database,฀including฀the฀following:

  ● ฀ Moves฀data฀to฀and฀from฀the฀physical฀data฀files฀as฀needed. ●

  ฀ Manages฀concurrent฀data฀access฀by฀multiple฀users,฀including฀provisions฀to฀prevent฀ simultaneous฀updates฀from฀conflicting฀with฀one฀another.

  ●

  ฀ Manages฀transactions฀so฀that฀each฀transaction’s฀database฀changes฀are฀an฀all-or-nothing฀ unit฀of฀work.฀In฀other฀words,฀if฀the฀transaction฀succeeds,฀all฀database฀changes฀made฀by฀ it฀are฀recorded฀in฀the฀database;฀if฀the฀transaction฀fails,฀none฀of฀the฀changes฀it฀made฀are฀ recorded฀in฀the฀database.

  ●

  ฀ Supports฀a฀query฀language,฀which฀is฀a฀system฀of฀commands฀that฀a฀database฀user฀ employs฀to฀retrieve฀data฀from฀the฀database.

  ● ฀ Provides฀provisions฀for฀backing฀up฀the฀database฀and฀recovering฀from฀failures. ● ฀ Provides฀security฀mechanisms฀to฀prevent฀unauthorized฀data฀access฀and฀modification.

  ฀ 6 ฀ Databases:฀A฀Beginner’s฀Guide Ask the Expert

  ฀ I’ve฀heard฀the฀term฀“data฀bank”฀used.฀What฀is฀the฀difference฀between฀a฀data฀bank฀and฀ Q: a฀database?

  ฀ A฀data฀bank฀and฀a฀database฀are฀the฀same฀thing.฀Data฀bank฀is฀merely฀an฀older฀term฀that฀was฀

A:

  used฀by฀the฀scientists฀who฀developed฀early฀database฀systems.฀In฀fact,฀the฀term฀data฀bank฀is฀ still฀used฀in฀a฀few฀human฀languages,฀such฀as฀banco฀de฀dados฀in฀Portuguese.

  Layers of Data Abstraction

  Databases฀are฀unique฀in฀their฀ability฀to฀present฀multiple฀users฀with฀their฀own฀distinct฀views฀ of฀the฀data฀while฀storing฀the฀underlying฀data฀only฀once.฀These฀are฀collectively฀called฀user฀

  views .฀A฀user฀in฀this฀context฀is฀any฀person฀or฀application฀that฀signs฀on฀to฀the฀database฀for฀

  the฀purpose฀of฀storing฀and/or฀retrieving฀data.฀An฀application฀is฀a฀set฀of฀computer฀programs฀ designed฀to฀solve฀a฀particular฀business฀problem,฀such฀as฀an฀order-entry฀system,฀a฀payroll- processing฀system,฀or฀an฀accounting฀system.

  When฀an฀electronic฀spreadsheet฀application฀such฀as฀Microsoft฀Excel฀is฀used,฀all฀ users฀must฀share฀a฀common฀view฀of฀the฀data,฀and฀that฀view฀must฀match฀the฀way฀the฀ data฀is฀physically฀stored฀in฀the฀underlying฀data฀file.฀If฀a฀user฀hides฀some฀columns฀in฀ a฀spreadsheet,฀reorders฀the฀rows,฀and฀saves฀the฀spreadsheet,฀the฀next฀user฀who฀opens฀ the฀spreadsheet฀will฀view฀the฀data฀in฀the฀manner฀in฀which฀the฀first฀user฀saved฀it.฀An฀ alternative,฀of฀course,฀is฀for฀each฀user฀to฀save฀his฀or฀her฀own฀copy฀in฀separate฀physical฀ files,฀but฀then฀as฀one฀user฀applies฀updates,฀the฀other฀users’฀data฀becomes฀out฀of฀date.฀ Database฀systems฀present฀each฀user฀a฀view฀of฀the฀same฀data,฀but฀the฀views฀can฀be฀tailored฀ to฀the฀needs฀of฀the฀individual฀users,฀even฀though฀they฀all฀come฀from฀one฀commonly฀stored฀ copy฀of฀the฀data.฀Because฀views฀store฀no฀actual฀data,฀they฀automatically฀reflect฀any฀data฀ changes฀made฀to฀the฀underlying฀database฀objects.฀This฀is฀all฀possible฀through฀layers฀of฀

  ,฀which฀is฀shown฀in฀Figure฀1-1.

  abstraction

  The฀architecture฀shown฀in฀Figure฀1-1฀was฀first฀developed฀by฀ANSI/SPARC฀(American฀ National฀Standards฀Institute/Standards฀Planning฀and฀Requirements฀Committee)฀in฀ the฀1970s฀and฀quickly฀became฀a฀foundation฀for฀much฀of฀the฀database฀research฀and฀ development฀efforts฀that฀followed.฀Most฀modern฀DBMSs฀follow฀this฀architecture,฀which฀ is฀composed฀of฀three฀primary฀layers:฀the฀physical฀layer,฀the฀logical฀layer,฀and฀the฀external฀ layer.฀The฀original฀architecture฀included฀a฀conceptual฀layer,฀which฀has฀been฀omitted฀here฀ because฀none฀of฀the฀modern฀database฀vendors฀implement฀it.

  ฀ Chapter฀1:฀ Database฀Fundamentals฀

  7 External Layer View 1 View 2 View 3 Logical Data Independence

  

Internal Schema

Logical Layer

(Logical Schema)

Physical Data

  Independence Physical Layer

File File File File File

Database Database Database Database Database

  Figure฀1-1 Database layers of abstraction

The Physical Layer

  The฀physical฀layer฀contains฀the฀data฀files฀that฀hold฀all฀the฀data฀for฀the฀database.฀Nearly฀all฀ modern฀DBMSs฀allow฀the฀database฀to฀be฀stored฀in฀multiple฀data฀files,฀which฀are฀usually฀ spread฀out฀over฀multiple฀physical฀disk฀drives.฀With฀this฀arrangement,฀the฀disk฀drives฀can฀ work฀in฀parallel฀for฀maximum฀performance.฀A฀notable฀exception฀among฀the฀DBMSs฀used฀ as฀examples฀in฀this฀book฀is฀Microsoft฀Access,฀which฀stores฀the฀entire฀database฀in฀a฀single฀ physical฀file.฀While฀simplifying฀database฀use฀on฀a฀single-user฀personal฀computer฀system,฀ this฀arrangement฀limits฀the฀ability฀of฀the฀DBMS฀to฀scale฀to฀accommodate฀many฀concurrent฀ users฀of฀the฀database,฀making฀it฀inappropriate฀as฀a฀solution฀for฀large฀enterprise฀systems.฀ In฀all฀fairness,฀Microsoft฀Access฀was฀not฀designed฀to฀be฀a฀robust฀enterprise฀class฀DBMS.฀I฀ have฀included฀it฀in฀discussions฀in฀this฀book฀not฀because฀it฀competes฀with฀products฀such฀as฀ Oracle฀and฀SQL฀Server,฀but฀because฀it’s฀a฀great฀example฀of฀a฀personal฀DBMS฀with฀a฀user฀ interface฀that฀makes฀learning฀database฀concepts฀easy฀and฀fun.

  The฀database฀user฀does฀not฀need฀to฀understand฀how฀the฀data฀is฀actually฀stored฀within฀ the฀data฀files฀or฀even฀which฀file฀contains฀the฀data฀item(s)฀of฀interest.฀In฀most฀organizations,฀ a฀technician฀known฀as฀a฀database฀administrator฀(DBA)฀handles฀the฀details฀of฀installing฀ and฀configuring฀the฀database฀software฀and฀data฀files฀and฀making฀the฀database฀available฀to฀ users.฀The฀DBMS฀works฀with฀the฀computer’s฀operating฀system฀to฀manage฀the฀data฀files฀ automatically,฀including฀all฀file฀opening,฀closing,฀reading,฀and฀writing฀operations.฀The฀database฀

  ฀ 8 ฀ Databases:฀A฀Beginner’s฀Guide

  user฀should฀not฀be฀required฀to฀refer฀to฀physical฀data฀files฀when฀using฀a฀database,฀which฀is฀ in฀sharp฀contrast฀with฀spreadsheets฀and฀word฀processing,฀where฀the฀user฀must฀consciously฀ save฀the฀document(s)฀and฀choose฀file฀names฀and฀storage฀locations.฀Many฀of฀the฀personal฀ computer–based฀DBMSs฀are฀exceptions฀to฀this฀tenet฀because฀the฀user฀is฀required฀to฀locate฀ and฀open฀a฀physical฀file฀as฀part฀of฀the฀process฀of฀signing฀on฀to฀the฀DBMS.฀Conversely,฀ with฀enterprise฀class฀DBMSs฀(such฀as฀Oracle,฀Sybase฀ASE,฀Microsoft฀SQL฀Server,฀and฀ MySQL),฀the฀physical฀files฀are฀managed฀automatically฀and฀the฀database฀user฀never฀needs฀to฀ refer฀to฀them฀when฀using฀the฀database.

The Logical Layer

  The฀logical฀layer฀or฀logical฀model฀comprises฀the฀first฀of฀two฀layers฀of฀abstraction฀in฀the฀ database:฀the฀physical฀layer฀has฀a฀concrete฀existence฀in฀the฀operating฀system฀files,฀whereas฀ the฀logical฀layer฀exists฀only฀as฀abstract฀data฀structures฀assembled฀from฀the฀physical฀layer฀as฀ needed.฀The฀DBMS฀transforms฀the฀data฀in฀the฀data฀files฀into฀a฀common฀structure.฀This฀layer฀ is฀sometimes฀called฀the฀schema,฀a฀term฀used฀for฀the฀collection฀of฀all฀the฀data฀items฀stored฀in฀ a฀particular฀database฀or฀belonging฀to฀a฀particular฀database฀user.฀Depending฀on฀the฀particular฀ DBMS,฀this฀layer฀can฀contain฀a฀set฀of฀two-dimensional฀tables,฀a฀hierarchical฀structure฀ similar฀to฀a฀company’s฀organization฀chart,฀or฀some฀other฀structure.฀The฀“Prevalent฀Database฀ Models”฀section฀later฀in฀this฀chapter฀describes฀the฀possible฀structures฀in฀more฀detail.

The External Layer

  The฀external฀layer฀or฀external฀model฀is฀the฀second฀layer฀of฀abstraction฀in฀the฀database.฀ This฀layer฀is฀composed฀of฀the฀user฀views฀discussed฀earlier,฀which฀are฀collectively฀ called฀the฀subschema.฀In฀this฀layer,฀the฀database฀users฀(application฀programs฀as฀well฀ as฀individuals)฀that฀access฀the฀database฀connect฀and฀issue฀queries฀against฀the฀database.฀ Ideally,฀only฀the฀DBA฀deals฀with฀the฀physical฀and฀logical฀layers.฀The฀DBMS฀handles฀the฀ transformation฀of฀selected฀items฀from฀one฀or฀more฀data฀structures฀in฀the฀logical฀layer฀ to฀form฀each฀user฀view.฀The฀user฀views฀in฀this฀layer฀can฀be฀predefined฀and฀stored฀in฀the฀ database฀for฀reuse,฀or฀they฀can฀be฀temporary฀items฀that฀are฀built฀by฀the฀DBMS฀to฀hold฀the฀ results฀of฀a฀single฀ad฀hoc฀database฀query฀until฀they฀are฀no฀longer฀needed฀by฀the฀database฀ user.฀An฀ad฀hoc฀query฀is฀a฀query฀that฀is฀not฀preconceived฀and฀that฀is฀not฀likely฀to฀be฀ reused.฀Views฀are฀discussed฀in฀more฀detail฀in฀Chapter฀2.

Physical Data Independence

  The฀ability฀to฀alter฀the฀physical฀file฀structure฀of฀a฀database฀without฀disrupting฀existing฀ users฀and฀processes฀is฀known฀as฀physical฀data฀independence.฀As฀shown฀in฀Figure฀1-1,฀the฀ separation฀of฀the฀physical฀layer฀from฀the฀logical฀layer฀provides฀physical฀data฀independence฀

  ฀ Chapter฀1:฀ Database฀Fundamentals฀

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