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Chapter 3
Database Architectures
and the Web
Multi-User DBMS Architectures
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Teleprocessing
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File-server
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Client-server
Teleprocessing
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Traditional architecture
Single mainframe with number of terminals
attached
File-Server
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File-server connected to several workstations
across network
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Database resides on file-server
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DBMS and applications run on each
workstation
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Disadvantages:
– Significant network traffic
– Copy of DBMS on each workstation
– Concurrency, recovery and integrity control more
complex
File-Server Architecture
Traditional Two-Tier Client-Server
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Client (tier 1) manages user interface and runs
applications
Server (tier 2) holds database and DBMS
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Advantages:
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wider access to existing databases
increased performance
possible reduction in hardware costs
reduction in communication costs
increased consistency
Traditional Two-Tier Client-Server
Traditional Two-Tier Client-Server
Three-Tier Client-Server
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Problems preventing true scalability in 2-tier:
– ‘Fat’ client, requiring considerable resources on
client’s computer to run effectively
– Significant client side administration overhead
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1995 - three layers proposed
Three-Tier Client-Server
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Advantages:
– ‘Thin’ client
» Requires less expensive hardware
– Application maintenance centralized
– Easier to modify/replace one tier without affecting
others
– Separation business logic from database functions
→ easier to implement load balancing
– Maps naturally to Web environment
Three-Tier Client-Server
Transaction Processing Monitors (TPM)
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Program that controls data transfer between
clients and servers in order to provide a
consistent environment, particularly for Online
Transaction Processing (OLTP).
TPM
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Transaction processing monitor
– Controls data transfer between clients/servers
– Provides a consistent environment, particularly
for online transaction processing (OLTP)
– Significant advantages
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Transaction routing
Managing distributed transactions
Load balancing
Funneling
Increased reliability
TPM as middle tier of 3-tier client-server
Multi-user DBMS Architectures
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Teleprocessing
– Traditional architecture for multi-user systems
– One computer with a single central processing
unit (CPU) and a number of terminals
– Put a huge burden on the central computer
Downsizing
– Replacing expensive mainframe computers
with more cost-effective networks of personal
computers
Multi-user DBMS Architectures
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File-server architecture
– Processing distributed about network
– Disadvantages:
» Large amount of network traffic
» Full copy of DBMS required on each workstation
» Concurrency, recovery, and integrity control are complex
Multi-user DBMS Architectures
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Traditional two-tier client–server architecture
– Client process requires some resource
– Server provides the resource
– Basic separation of four main components of
business application
– Typical interaction between client and server
Summary of client–server functions
Multi-user DBMS Architectures
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Three-tier client–server architecture
– User interface layer
– Business logic and data processing layer
– DBMS
– Many advantages over traditional two-tier or
single-tier designs
Multi-user DBMS Architectures
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N-tier architectures
– Three-tier architecture can be expanded to n
tiers
Application servers
– Hosts an application programming interface
(API) to expose business logic and business
processes for use by other applications
Multi-user DBMS Architectures
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Middleware
– Software that mediates with other software
– Communication among disparate applications
– Six main types
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Asynchronous Remote Procedure Call (RPC)
Synchronous RPC
Publish/Subscribe
Message-Oriented middleware (MOM)
Object-request broker (ORB)
SQL-oriented data access
Web Services and Service-Oriented
Architectures
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Web service
– Software system that supports interoperable
machine-to-machine interaction over network
– No user interface
– Examples of Web services
» Microsoft Virtual Earth Web service
– Uses widely accepted technologies and
standards
Web Services and Service-Oriented
Architectures
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Service-Oriented Architectures (SOA)
– Architecture for building applications that
implement business processes as sets of
services
Some principles built upon:
– Loose coupling
– Reusability
– Composability
Traditional vs. SOA Architecture
Distributed DBMSs
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Distributed database
– Logically interrelated collection of shared data
physically (single database) distributed over
network
Distributed DBMS
– Software system that permits management of
distributed database
– Distribution transparent to users
Distributed DBMSs
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Characteristics of DDBMS
– Collection of logically related shared data
– Data split into fragments
– Fragments may be replicated
– Fragments/replicas allocated to sites
– Sites linked by communications network
– Data at each site controlled by DBMS
– DMBS handles local apps autonomously
– Each DBMS in one or more global app
Distributed DBMSs
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Distributed processing
– Centralized database that can be accessed over
computer network
System consists of data physically distributed
across number of sites in network
Data Warehousing
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Data warehouse
– Consolidated/integrated view of corporate data
– Drawn from disparate operational data sources
– Range of end-user access tools capable of
supporting simple to highly complex queries to
support decision making
– Subject-oriented, integrated, time-variant, and
nonvolatile
Typical Architecture of a Data Warehouse
Components of a DBMS
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Major components of a DBMS:
– Query processor
– Database manager (DM)
– File manager
– DML preprocessor
– DDL compiler
– Catalog manager
Components of a DBMS
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Major software components for database manager
– Transaction manager
– Authorization control
– Scheduler
– Command processor
– Recovery manager
– Integrity checker
– Buffer manager
– Query optimizer
Oracle Architecture
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Oracle’s logical database structure
– Tablespaces
– Schemas
– Data blocks
– Extents/segments
Relationship between an Oracle Database,
Tablespaces, and Datafiles
Oracle Architecture
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Oracle’s physical database structure
– Datafiles
– Redo log files
– Control files
The Oracle instance
– Oracle processes and shared memory required
to access information in the database