1 Chapter 9: The Client/Server Database Environment Modern Database Management 7 th Edition Jeffrey A. Hoffer, Mary B. Prescott, Fred R. McFadden.

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Chapter 9:Chapter 9: The Client/Server The Client/Server

Database EnvironmentDatabase EnvironmentModern Database ManagementModern Database Management

77thth Edition EditionJeffrey A. Hoffer, Mary B. Prescott, Jeffrey A. Hoffer, Mary B. Prescott,

Fred R. McFaddenFred R. McFadden

22Chapter 9

ObjectivesObjectives Definition of termsDefinition of terms List advantages of client/server architectureList advantages of client/server architecture Explain three application components: presentation, Explain three application components: presentation,

processing, and storageprocessing, and storage Suggest partitioning possibilitiesSuggest partitioning possibilities Distinguish between file server, database server, 3-tier, Distinguish between file server, database server, 3-tier,

and n-tier approachesand n-tier approaches Describe and discuss middlewareDescribe and discuss middleware Explain query-by-example (QBE)Explain query-by-example (QBE) Explain database linking via ODBC and JDBCExplain database linking via ODBC and JDBC Explain VBA and Microsoft AccessExplain VBA and Microsoft Access

33Chapter 9

Client/Server SystemsClient/Server Systems

Networked computing modelNetworked computing model Processes distributed between clients and Processes distributed between clients and

serversservers Client – Workstation (usually a PC) that Client – Workstation (usually a PC) that

requests and uses a servicerequests and uses a service Server – Computer (PC/mini/mainframe) Server – Computer (PC/mini/mainframe)

that provides a servicethat provides a service For DBMS, server is a database serverFor DBMS, server is a database server

44Chapter 9

Application Logic in C/S Application Logic in C/S SystemsSystems

GUI Interface

Procedures, functions,programs

DBMS activities

Processing LogicProcessing Logic I/O processingI/O processing Business rulesBusiness rules Data managementData management

Storage LogicStorage Logic Data storage/retrievalData storage/retrieval

Presentation LogicPresentation Logic Input – keyboard/mouseInput – keyboard/mouse Output – monitor/printerOutput – monitor/printer

55Chapter 9

Client/Server ArchitecturesClient/Server Architectures

File Server ArchitectureFile Server Architecture

Database Server ArchitectureDatabase Server Architecture

Three-tier ArchitectureThree-tier Architecture

Client does extensive processing

Client does little processing

66Chapter 9

File Server ArchitectureFile Server Architecture

All processing is done at the PC that requested All processing is done at the PC that requested the data the data

Entire files are transferred from the server to the Entire files are transferred from the server to the client for processingclient for processing

Problems:Problems: Huge amount of data transfer on the networkHuge amount of data transfer on the network Each client must contain full DBMS Each client must contain full DBMS

• Heavy resource demand on clientsHeavy resource demand on clients• Client DBMSs must recognize shared locks, integrity checks, Client DBMSs must recognize shared locks, integrity checks,

etc.etc.

FAT FAT CLIENTCLIENT

77Chapter 9

Figure 9-2: File Server Architecture

FAT FAT CLIENTCLIENT

88Chapter 9

Two-Tier Database Server Two-Tier Database Server ArchitecturesArchitectures

Client is responsible for Client is responsible for I/O processing logic I/O processing logic Some business rules logicSome business rules logic

Server performs all data storage and Server performs all data storage and access processing access processing DBMS is only on serverDBMS is only on server

99Chapter 9

Advantages of Two-Tier ApproachAdvantages of Two-Tier Approach

Clients do not have to be as powerfulClients do not have to be as powerful Greatly reduces data traffic on the Greatly reduces data traffic on the

networknetwork Improved data integrity since it is all Improved data integrity since it is all

processed centrallyprocessed centrally Stored proceduresStored procedures some business some business

rules done on serverrules done on server

1010Chapter 9

Advantages of Advantages of Stored ProceduresStored Procedures

Compiled SQL statementsCompiled SQL statementsReduced network trafficReduced network traffic Improved securityImproved security Improved data integrityImproved data integrityThinner clientsThinner clients

1111Chapter 9

Figure 9-3: Two-tier database server architecture

ThinneThinner r clientsclients

DBMS DBMS only on only on serverserver

1212Chapter 9

Three-Tier ArchitecturesThree-Tier Architectures

Thin Client PC just for user interface and a little application

processing. Limited or no data storage (sometimes no hard drive)

GUI interface (I/O processing)

Browser

Business rules Web Server

Data storage DBMS

Client

Application server

Database server

1313Chapter 9

Figure 9-4: Three-tier architecture

Thinnest Thinnest clientsclients

Business rules on Business rules on separate serverseparate server

DBMS only DBMS only on DB serveron DB server

1414Chapter 9

Advantages of Three-Tier Advantages of Three-Tier ArchitecturesArchitectures

ScalabilityScalability Technological flexibilityTechnological flexibility Long-term cost reductionLong-term cost reduction Better match of systems to business Better match of systems to business

needsneeds Improved customer serviceImproved customer service Competitive advantageCompetitive advantage Reduced riskReduced risk

1515Chapter 9

Challenges of Three-tier Challenges of Three-tier ArchitecturesArchitectures

High short-term costsHigh short-term costsTools and trainingTools and trainingExperienceExperience Incompatible standardsIncompatible standardsLack of compatible end-user toolsLack of compatible end-user tools

1616Chapter 9

Application PartitioningApplication Partitioning

Placing portions of the application code in Placing portions of the application code in different locations (client vs. server) different locations (client vs. server) AFTER it is writtenAFTER it is written

AdvantagesAdvantages Improved performanceImproved performance Improved interoperabilityImproved interoperability Balanced workloadsBalanced workloads

1717Chapter 9

Parallel Computer ArchitecturesParallel Computer Architectures

Tightly CoupledTightly Coupled Symmetric Multiprocessing (SMP)Symmetric Multiprocessing (SMP) Multiple CPUsMultiple CPUs Shared RAMShared RAM

Loosely CoupledLoosely Coupled Massively Parallel Processing (MPP)Massively Parallel Processing (MPP) Multiple CPUsMultiple CPUs Each CPU has its own RAM spaceEach CPU has its own RAM space

1818Chapter 9

Parallel Computer ArchitecturesParallel Computer Architectures

Figure 9-6Tightly coupled – CPUs share common memory space

Figure 9-7Loosely coupled – CPUs each have their own memory space

1919Chapter 9

Query Processing with Query Processing with Parallel ProcessorsParallel Processors

Figure 9-5a:Parallel transactions

Figure 9-5b:Parallel query

2020Chapter 9

Processing Logic DistributionsProcessing Logic Distributions

Two-tier distributions

n-tier distributions

Processing logic could be at client, server, or both

Processing logic will be at application server or Web server

2121Chapter 9

MiddlewareMiddleware

Software which allows an application to Software which allows an application to interoperate with other software with other software

No need for programmer/user to No need for programmer/user to understand internal processingunderstand internal processing

Accomplished via Accomplished via Application Program Interface (API)(API)

The “glue”“glue” that holds client/server applications together

2222Chapter 9

Types of MiddlewareTypes of Middleware Remote Procedure Calls (RPC) Remote Procedure Calls (RPC)

client makes calls to procedures running on remote computersclient makes calls to procedures running on remote computers synchronous and asynchronoussynchronous and asynchronous

Message-Oriented Middleware (MOM) Message-Oriented Middleware (MOM) asynchronous calls between the client via message queuesasynchronous calls between the client via message queues

Publish/SubscribePublish/Subscribe push technology push technology server sends information to client when available server sends information to client when available

Object Request Broker (ORB)Object Request Broker (ORB) object-oriented management of communications between clients and object-oriented management of communications between clients and

serversservers

SQL-oriented Data AccessSQL-oriented Data Access middleware between applications and database serversmiddleware between applications and database servers

2323Chapter 9

Database MiddlewareDatabase Middleware

ODBCODBC – Open Database Connectivity – Open Database Connectivity Most DB vendors support thisMost DB vendors support this

OLE-DBOLE-DB Microsoft enhancement of ODBCMicrosoft enhancement of ODBC

JDBCJDBC – Java Database Connectivity – Java Database Connectivity Special Java classes that allow Java Special Java classes that allow Java

applications/applets to connect to databasesapplications/applets to connect to databases

2424Chapter 9

Client/Server SecurityClient/Server Security Network environment Network environment complex security complex security

issuesissues Security levels:Security levels:

System-level password securitySystem-level password security• for allowing access to the systemfor allowing access to the system

Database-level password securityDatabase-level password security• for determining access privileges to tables; for determining access privileges to tables;

read/update/insert/delete privilegesread/update/insert/delete privileges Secure client/server communication Secure client/server communication

• via encryptionvia encryption

2525Chapter 9

Query-by-Example (QBE)Query-by-Example (QBE)

Direct-manipulation database languageDirect-manipulation database language Graphical approachGraphical approach Available in MS AccessAvailable in MS Access MS Access translates QBE to SQL and vice MS Access translates QBE to SQL and vice

versaversa Useful for end-user database programmingUseful for end-user database programming Good for ad hoc processing and prototypingGood for ad hoc processing and prototyping

2626Chapter 9

Figure 9-10: QBE view of a multiple-table join query

Figure 9-12: Equivalent query in SQL

2727Chapter 9

Figure 9-9: Access usability hierarchy

Foundation of MS Access

Simple processes

Stored modules of pre-existing VBA code

Visual Basic for Applications…language for customizing the application

API to call functions in DLLs external to MS Access

2828Chapter 9

Using ODBC to Link External Databases Using ODBC to Link External Databases Stored on a Database ServerStored on a Database Server

Open Database Connectivity (ODBC)Open Database Connectivity (ODBC) API that provides a common language for application programs to API that provides a common language for application programs to

access and process SQL databases independent of the particular access and process SQL databases independent of the particular RDBMS that is accessedRDBMS that is accessed

Required parameters:Required parameters: ODBC driver ODBC driver Back-end server nameBack-end server name Database nameDatabase name User id and passwordUser id and password

Additional information:Additional information: Data source name (DSN)Data source name (DSN) Windows client computer nameWindows client computer name Client application program’s executable nameClient application program’s executable name

Java Database Connectivity (JDBC) is similar to ODBC – built specifically for Java applications

2929Chapter 9

ODBC Architecture ODBC Architecture (Figure 9-18)(Figure 9-18)

Each DBMS has its own ODBC-compliant driver

Client does not need to know anything about the DBMS

Application Program Interface (API) provides common interface to all DBMSs

3030Chapter 9

Visual Basic for ApplicationsVisual Basic for Applications VBA is the programming language that VBA is the programming language that

accompanies Access 2000accompanies Access 2000 VBA provides these features:VBA provides these features:

Ability to perform complex functionalityAbility to perform complex functionality Error handlingError handling Faster execution than macrosFaster execution than macros Easier maintenanceEasier maintenance OLE automationOLE automation Programmatic controlProgrammatic control Ease of reading for programmersEase of reading for programmers

Event-driven – nonprocedural programming that Event-driven – nonprocedural programming that detects events and generates appropriate responsesdetects events and generates appropriate responses