The Database Environment Chapter 9

1
© Prentice Hall, 2002
Chapter 9:Chapter 9:
The Client/Server DatabaseThe Client/Server Database
EnvironmentEnvironment
Modern Database Management
6th
Edition
Jeffrey A. Hoffer, Mary B. Prescott, Fred R.
McFadden

2Chapter 9 © Prentice Hall,
Client/Server SystemsClient/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

Application Logic in C/SApplication Logic in C/S
SystemsSystems
 Presentation Logic
– Input – keyboard/mouse
– Output – monitor/printer
 Processing Logic
– I/O processing
– Business rules
– Data management
 Storage Logic
– Data storage/retrieval
GUI Interface
Procedures, functions,
programs
DBMS activities

Client/Server ArchitecturesClient/Server Architectures
File Server Architecture
Database Server Architecture
Three-tier Architecture
Client does
extensive processing
Client does little
processing

File Server ArchitectureFile Server Architecture
 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.
FATFAT
CLIENTCLIENT

Figure 9-2 – File Server Architecture
FATFAT
CLIENTCLIENT

Database Server ArchitecturesDatabase Server Architectures
 2-tiered approach
 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
 Advantages
– 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  some business rules done on server

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

Figure 9-3 – Database server architecture
ThinneThinne
rr
clientsclients
DBMS onlyDBMS only
on serveron server

Three-Tier ArchitecturesThree-Tier Architectures
Three layers:
– Client
– Application server
– Database 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

Figure 9-4 -- Three-tier architecture
ThinnestThinnest
clientsclients
Business rules onBusiness rules on
separate serverseparate server
DBMS only onDBMS only on
DB serverDB server

Advantages of Three-TierAdvantages of Three-Tier
ArchitecturesArchitectures
Scalability
Technological flexibility
Long-term cost reduction
Better match of systems to business needs
Improved customer service
Competitive advantage
Reduced risk

Challenges of Three-tierChallenges of Three-tier
High short-term costs
Tools and training
Experience
Incompatible standards
Lack of compatible end-user tools

Application PartitioningApplication Partitioning
Placing portions of the application code in
different locations (client vs. server)
AFTER it is written
Advantages
– Improve performance
– Improve interoperability
– Balanced workloads

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

Parallel ComputerParallel Computer
Tightly Coupled
– Symmetric Multiprocessing (SMP)
– Multiple CPUs
– Shared RAM
Loosely Coupled
– Massively Parallel Processing (MPP)
– Multiple CPUs
– Each CPU has its own RAM space

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

Query Processing withQuery Processing with
Parallel ProcessorsParallel Processors
Figure 9-5(a) –
Parallel transactions
Figure 9-5(b) –
Parallel query

MiddlewareMiddleware
Software which allows an application to
interoperateinteroperate with other software
No need for programmer/user to understand
internal processing
Accomplished via Application ProgramApplication Program
InterfaceInterface (API)
The “glue”“glue” that holds client/server applications together

Types of MiddlewareTypes of Middleware
 RPC – 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

Database MiddlewareDatabase 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

Client/Server SecurityClient/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

Query-by-Example (QBE)Query-by-Example (QBE)
Direct-manipulation database language
Graphical approach
Available in MS Access
MS Access translates QBE to SQL and vice
versa
Useful for end-user database programming
Good for ad hoc processing and prototyping

Figure 9-10:
QBE view of
a 2-table join
query
Figure 9-12:
Equivalent
query in SQL

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

Using ODBC to Link External DatabasesUsing ODBC to Link External Databases
Stored on a Database ServerStored on a Database Server
 Open Database Connectivity (ODBC)
– API that 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

ODBC ArchitectureODBC 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

Visual Basic for ApplicationsVisual Basic for Applications
VBA is the programming language that
accompanies Access 2000
VBA provides these features:
– Ability to perform complex functionality
– Error handling
– Faster execution than macros
– Easier maintenance
– OLE automation
– Programmatic control
– Ease of reading for programmers
 Event-driven – nonprocedural programming that detects
events and generates appropriate responses

The Database Environment Chapter 9

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The Database Environment Chapter 9