Chapter 9: The Client/Server Database Environment

11

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

Database EnvironmentDatabase Environment

22Chapter 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

33Chapter 9

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

Presentation LogicPresentation Logic• Input – Input –

keyboard/mousekeyboard/mouse• Output – Output –

monitor/printermonitor/printer Processing LogicProcessing Logic

• I/O processingI/O processing• Business rulesBusiness rules• Data managementData management

Storage LogicStorage Logic• Data storage/retrievalData storage/retrieval

GUI Interface

Procedures, functions,programs

DBMS activities

44Chapter 9

Client/Server ArchitecturesClient/Server Architectures

File Server ArchitectureFile Server Architecture

Database Server Database Server

ArchitectureArchitecture

Three-tier ArchitectureThree-tier Architecture

Client does extensive processing

Client does little processing

55Chapter 9

File Server ArchitectureFile Server Architecture

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

Entire files are transferred from the server Entire files are transferred from the server to the client for processing.to the client 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 Client DBMSs must recognize shared locks, integrity

checks, etc.checks, etc.

FAT FAT CLIENTCLIENT

66Chapter 9

Figure 9-2 – File Server Architecture

FAT FAT CLIENTCLIENT

77Chapter 9

Database Server ArchitecturesDatabase Server Architectures 2-tiered approach2-tiered approach 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 access Server performs all data storage and access processing processing DBMS is only on serverDBMS is only on server

AdvantagesAdvantages• Clients do not have to be as powerfulClients do not have to be as powerful• Greatly reduces data traffic on the networkGreatly reduces data traffic on the network• Improved data integrity since it is all processed centrallyImproved data integrity since it is all processed centrally• Stored proceduresStored procedures some business rules done on some business rules done on

serverserver

88Chapter 9

Advantages of Advantages of Stored ProceduresStored Procedures

Compiled SQL statementsCompiled SQL statements Reduced network trafficReduced network traffic Improved securityImproved security Improved data integrityImproved data integrity Thinner clientsThinner clients

99Chapter 9

Figure 9-3 – Database server architecture

ThinneThinner r clientsclients

DBMS DBMS only on only on serverserver

1010Chapter 9

Three-Tier ArchitecturesThree-Tier Architectures

Three layers:Three layers:• ClientClient• Application serverApplication server• Database serverDatabase server

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

1111Chapter 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

1212Chapter 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 needsBetter match of systems to business needs Improved customer serviceImproved customer service Competitive advantageCompetitive advantage Reduced riskReduced risk

1313Chapter 9

Challenges of Three-tier Challenges of Three-tier ArchitecturesArchitectures

High short-term costsHigh short-term costs Tools and trainingTools and training ExperienceExperience Incompatible standardsIncompatible standards Lack of compatible end-user Lack of compatible end-user

toolstools

1414Chapter 9

Application PartitioningApplication Partitioning Placing portions of the application Placing portions of the application

code in different locations (client vs. code in different locations (client vs. server) AFTER it is writtenserver) AFTER it is written

AdvantagesAdvantages• Improve performanceImprove performance• Improve interoperabilityImprove interoperability• Balanced workloadsBalanced workloads

1515Chapter 9

Processing Logic DistributionsProcessing Logic Distributions

2-tier distributions

n-tier distributions

Processing logic could be at client, server, or both

Processing logic will be at application server or Web server

1616Chapter 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

1717Chapter 9

Parallel Computer ArchitecturesParallel Computer Architectures

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

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

1818Chapter 9

Query Processing with Query Processing with Parallel ProcessorsParallel Processors

Figure 9-5(a) –Parallel transactions

Figure 9-5(b) –Parallel query

1919Chapter 9

MiddlewareMiddleware

Software which allows an application Software which allows an application to to interoperateinteroperate 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 Application Program InterfaceProgram Interface (API) (API)

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

2020Chapter 9

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

• client makes calls to procedures running on remote client makes calls to procedures running on remote computerscomputers

• 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 server sends information to client when availableavailable

Object Request Broker (ORB)Object Request Broker (ORB)• Object-oriented management of communications between Object-oriented management of communications between

clients and serversclients and servers SQL-oriented Data AccessSQL-oriented Data Access

• Middleware between applications and database serversMiddleware between applications and database servers

2121Chapter 9

Database MiddlewareDatabase Middleware

ODBC – Open Database ODBC – Open Database ConnectivityConnectivity• Most DB vendors support thisMost DB vendors support this

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

JDBC – Java Database ConnectivityJDBC – Java Database Connectivity• Special Java classes that allow Java Special Java classes that allow Java

applications/applets to connect to applications/applets to connect to databasesdatabases

2222Chapter 9

Web ServicesWeb Services XML – Extensible Markup Language, W3C XML – Extensible Markup Language, W3C

standard in 1998.standard in 1998. SOAP - Simple Object Access Protocol extensible SOAP - Simple Object Access Protocol extensible

framing mechanism for XML messages framing mechanism for XML messages UDDI - Universal Description, Discovery, and UDDI - Universal Description, Discovery, and

Integration (UDDI), defines a SOAP-based API for Integration (UDDI), defines a SOAP-based API for querying centralized Web Service repositories . querying centralized Web Service repositories .

WSDL -Web Services Description Language WSDL WSDL -Web Services Description Language WSDL is an XML format for describing network services is an XML format for describing network services as a set of endpoints operating on messages as a set of endpoints operating on messages containing either document-oriented or containing either document-oriented or procedure-oriented information procedure-oriented information

2323Chapter 9

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

security issuessecurity issues 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

2424Chapter 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 Good for ad hoc processing and

prototypingprototyping

2525Chapter 9

Figure 9-10: QBE view of a 2-table join query

Figure 9-12: Equivalent query in SQL