Chap 09 Corrected

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Chapter 9

Chapter 9:

The Client/ServerDatabase

EnvironmentModern Database Management

8

th

EditionJeffrey A. Hoffer, Mary B. Prescott,

Fred R. McFadden

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Chapter 9

Objectives

Definition of terms

List advantages of client/server architecture

Explain three application components: presentation,

processing, and storage

Suggest partitioning possibilities

Distinguish between file server, database server, 3-

tier, and n-tier approaches Describe and discuss middleware

Explain database linking via ODBC and JDBC 2

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Chapter 9

Client/Server Systems

Networked computing model

Processes distributed between clients and servers

ClientWorkstation (usually a PC) that requests and uses aservice

ServerComputer (PC/mini/mainframe) that provides aservice

For DBMS, server is a database server

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Chapter 9

Application Logic in C/S

Systems

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GUI Interface

Procedures, functions,

programs

DBMS activities

Processing Logic I/O processing

Business rules

Data management

Storage Logic Data storage/retrieval

Presentation Logic

Inputkeyboard/mouse

Outputmonitor/printer

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Chapter 9

Client/Server Architectures

File Server Architecture

Database Server Architecture

Three-tier Architecture

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Client does

extensive processing

Client does little

processing

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Chapter 9

File Server Architecture

All processing is done at the PC that requested the

data

Entire files are transferred from the server to theclient for processing

Problems:

Huge amount of data transfer on the network

Each client must contain full DBMS

Heavy resource demand on clients

Client DBMSs must recognize shared locks, integrity checks, etc. 6

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Chapter 9

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Figure 9-2 File Server Architecture

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Chapter 9

Two-Tier Database Server

Architectures

Client is responsible for

I/O processing logic

Some business rules logic Server performs all data storage and

access processing

DBMS is only on server

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Chapter 9

Advantages of Two-Tier Approach

Clients do not have to be as powerful

Greatly reduces data traffic on the network

Improved data integrity since it is all processed centrally

Stored procedures DBMS code that performs some business rulesdone on server

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Chapter 9

Advantages of

Stored Procedures

Compiled SQL statements

Reduced network traffic

Improved security

Improved data integrity

Thinner clients

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Chapter 9

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Figure 9-3 Two-tier database server architecture

DBMS onlyon server

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Chapter 9

Three-Tier Architectures

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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

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Chapter 9

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Figure 9-4 Three-tier architecture

Thinnestclients

Business ruleson separateserver

DBMS only onDB server

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Chapter 9

Advantages of Three-Tier

Architectures Scalability

Technological flexibility

Long-term cost reduction

Better match of systems to business needs

Improved customer service

Competitive advantage

Reduced risk

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Chapter 9

Application Partitioning

Placing portions of the application code in different locations (client

vs. server) AFTER it is written

Advantages

Improved performance

Improved interoperability

Balanced workloads

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Chapter 9

Common Logic Distributions

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Figure 9-5a Two-tier client-

server environment

Figure 9-5b n-tier client-

server environment

Processing logic could be

at client, server, or both

Processing logicwill be at

application server

or Web server

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Chapter 9

Role of the Mainframe

Mission-critical legacy systems have tended to remain onmainframes

Distributed client/server systems tend to be used for smaller,workgroup systems

Difficulties in moving mission critical systems from mainframeto distributed

Determining which code belongs on server vs. client

Identifying potential conflicts with code from other applications

Ensuring sufficient resources exist for anticipated load

Rule of thumb Mainframe for centralized data that does not need to be moved

Client for data requiring frequent user access, complex graphics, anduser interface 17

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Chapter 9

Middleware

Software that allows an application to interoperate with othersoftware

No need for programmer/user to understand internal processing

Accomplished viaApplication Program Interface(API)

18The gluethat holds client/server applications together

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Chapter 9

Types of Middleware

Remote Procedure Calls (RPC) client makes calls to procedures running on remote computers

synchronous and asynchronous

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

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

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

servers SQL-oriented Data Access

middleware between applications and database servers19

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Chapter 9

Database Middleware

ODBCOpen Database Connectivity Most DB vendors support this

OLE-DB Microsoft enhancement of ODBC

JDBCJava Database Connectivity Special Java classes that allow Java applications/applets to connect to

databases

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Chapter 9

Client/Server Security

Network environment complex security issues Security levels:

System-level password security

for allowing access to the system

Database-level password security

for determining access privileges to tables; read/update/insert/deleteprivileges

Secure client/server communication

via encryption

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Chapter 9

Keys to Successful Client-Server

Implementation

Accurate business problem analysis

Detailed architecture analysis

Architecture analysis before choosing tools Appropriate scalability

Appropriate placement of services

Network analysis

Awareness of hidden costs

Establish client/server security22

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Chapter 9

Benefits of Moving to Client/Server

Architecture Staged delivery of functionality speeds deployment

GUI interfaces ease application use

Flexibility and scalability facilitates business processreengineering

Reduced network traffic due to increased processing at datasource

Facilitation of Web-enabled applications

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Chapter 9

Using ODBC to Link External Databases Stored

on a Database Server Open Database Connectivity (ODBC)

API provides a common language for application programs toaccess and process SQL databases independent of the particularRDBMS that is accessed

Required parameters:

ODBC driver

Back-end server name

Database name

User id and password

Additional information:

Data source name (DSN)

Windows client computer name

Client application programs executable name

24Java Database Connectivity (JDBC) is similar to ODBCbuilt specifically for Java applications

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Chapter 9

ODBC Architecture(Figure 9-6)

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Each DBMS has its own ODBC-compliant driver

Client does not need toknow anything about theDBMS

Application Program

Interface (API) providescommon interface to allDBMSs

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Documents

Chap 09 Corrected