Database Management Environment

The Client/Server Architecture

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 System Architecture

• The architecture of a computer system is the

high-level (most general) design on which the
system is based

• Architectural features include:

– Components
– Collaborations (how components interact)
– Connectors (how components communicate)
 System Architecture

• Common architectural patterns include

– Client-Server
– Layered
– Peer-to-peer
– Pipes and Filters
– etc.
 Client/Server Systems
• Networked computing model
• Processes distributed between clients and
servers
• Client–Workstation (usually a PC) that
requests and uses a service
• Server–Computer (PC/mini/mainframe) that
provides a service
• For DBMS, server is a database server

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 Application Logic in C/S Systems
Presentation Logic
 Input–keyboard/mouse
GUI Interface
 Output–monitor/printer

Processing Logic
 I/O processing Procedures, functions,
 Business rules programs
 Data manipulation

Storage Logic
 Data storage/retrieval DBMS activities

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 Centralized / Distributed

• The client-server architecture can be thought

of as a median between
– Centralized processing: computation is performed
on a central platform, which is accessed using
“dumb” terminals
– Distributed processing: computation is performed
on platforms located with the user

Centralized Client / Server Distributed

 Client-Server Architecture

Example: The Web is a client-server system

• Web browsers act as clients, and make
requests to web servers
• Web servers respond to requests with
requested information and/or computation
Client
Client Server
Client Server

request
Client
Client Server
 Tiered Web Architectures

• Web applications are usually implemented

with 2-tier, 3-tier, or multitier (N-tier)
architectures

• Each tier is a platform (client or server) with a

unique responsibility
 Client/Server Architectures
Client does
extensive processing
• File Server Architecture

• Database Server Architecture

Client does little

processing

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 File Server Architecture
FAT CLIENT
• All processing is done at the PC that requested the
data
• Entire files are transferred from the server to the
client 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.

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 File Server Architecture

FAT CLIENT

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 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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 Two-tier database server architecture

Thinner
clients

DBMS only
on server

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 Advantages of database 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
• Allows use of Stored procedures  DBMS code
that performs some business rules done on
server

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 Advantages of Stored Procedures
• Compiled SQL statements
• Reduced network traffic
• Improved security
• Improved data integrity
• Thinner clients

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 Three-Tier Architecture

GUI interface Browser

Client (I/O processing)

Application server Business rules Web Server

Database server Data storage DBMS

Thin Client
 PC just for user interface and a little application
processing. Limited or no data storage (sometimes no
hard drive)
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 Three-tier architecture

Thinnest
clients

Business rules on
separate server

DBMS only on DB
server

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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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 Multitier C-S Architecture
• A multitier (N-tier) architecture is an
expansion of the 3-tier architecture, in one of
several different possible ways
– Replication of the function of a tier
– Specialization of function within a tier
– Portal services, focusing on handling incoming
web traffic
 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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 Common Logic Distributions
Two-tier client-server
environment

Processing logic could be

at client, server, or both

n-tier client-server
environment
Processing logic
will be at
application server
or Web server

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 Role of the Mainframe
• Mission-critical legacy systems have tended to remain on
mainframes
• Distributed client/server systems tend to be used for smaller,
workgroup systems
• Difficulties in moving mission critical systems from mainframe
to 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, and
user interface

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 Middleware

• Software that allows an application to

interoperate with other software
• No need for programmer/user to understand
internal processing
• Accomplished via Application Program
Interface (API)

The “glue” that holds client/server applications together

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 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 servers

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 Database Middleware
• ODBC–Open Database Connectivity
– Most DB vendors support this
• OLE-DB
– Microsoft enhancement of ODBC
• JDBC–Java Database Connectivity
– Special Java classes that allow Java
applications/applets to connect to databases

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 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/delete privileges
– Secure client/server communication
• via encryption

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 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 security

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 Benefits of Moving to Client/Server
Architecture
• Staged delivery of functionality speeds
deployment
• GUI interfaces ease application use
• Flexibility and scalability facilitates business
process reengineering
• Reduced network traffic due to increased
processing at data source
• Facilitation of Web-enabled applications

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 Using ODBC to Link External Databases Stored
on a Database Server
• Open Database Connectivity (ODBC)
– API provides a common language for application programs to access and
process SQL databases independent of the particular RDBMS 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 program’s executable name

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

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ODBC Architecture

Client does not need to

know anything about the
DBMS
Application Program
Interface (API) provides
common interface to all
DBMSs

Each DBMS has its own ODBC-compliant driver

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 Characteristics Summary

•large e-commerce, business, or

N-Tier organization
1000
•small e-commerce, regional
users 3-Tier
business or organization
100
2-Tier •local business or organization
10

capacity
scalability
redundancy
cost
 Additional Reading
• Modern Database Management 8th Edition by
Jeffrey A. Hoffer, Mary B. Prescott, Fred R.
McFadden – Chapter 9

• Rai Foundation Notes – Lectures 19 and 19a