Download Database Management System 2

DATABASE
MANAGEMENT SYSTEMS 2
ANGELITO I. CUNANAN JR.
I. Database Management Systems
Approaches…
•
Client/Server Systems
Advantages
• Disadvantages
•
•
Distributed Database
Characteristics of DBMSs
• Advantages
• Disadvantages
• Rules for distributed database
•
•
Centralized Database
Advantages
• Disadvantages
•
•
Federated Database
FDBS Architecture
• 5 Level Schema
•
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Client/Server Systems…
File Server stores the files required by the users on the network.
When users need data from file or a group of files, they send
requests to the file server. The file server then sends the requested
file or files to the user’s computer; that is, the file server sends entire
files, not just the data need by users.
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Client/Server
Systems…(continued)
USER
B
USER
A
User requests
file(s) from
the file server
USER
C
NETWORK
File server sends
requested file(s)
to the user
FILES ON DISK
FILE
SERVER
File server architecture
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Client/Server
Systems…(continued)
In Client/Server terminology, the Server is a computer providing
data to the clients, which are the computers that are connected to a
network and that people use to access data stored on the server.
• Server is also called a back-end processor or back-end machine.
• Client is also called a front-end processor or front-end machine.
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Guide…
• In client/server architecture, DBMS runs on the server.
• Client sends a request to the server, not entire files but for specific
data.
• Compared to a file server architecture, a client/server architecture
reduces communication activity on a network, which reduces
delays in supplying data to users.
• Clients & Server: Performs different functions, can run in different
OS, this arrangement of client/server architecture is called two-tier
architecture.
• Server – performs database function, client – performs
presentation function (user interface function).
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Guide…(continued)
• Business function – Calculations, commissions, taxes, and order
totals.
• Fat client – Client perform business functions. (Client maintenance
problem).
• Thin client – Server performs business functions. (Scalability
problem).
• Scalability – Is the ability of a computer system to continue to
function well as utilization of the system increases.
• Three-tier architecture – Client perform presentation functions,
Database Server performs database function, and separate
computer (called Application servers) perform business functions
and serves as interface between client and database server. (also
referred to n-tier architecture).
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Client/Server
Systems…(continued)
Fat Client
Thin Client
Scalability
Three-tier architecture
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Client/Server
Systems…(continued)
USER
B
USER
A
User requests
data from
database
USER
C
NETWORK
Servers ends only
requested data to
the client that
requested it
DATABASE
SERVER
WITH A
DBMS
Two-tier client/server
architecture
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Client/Server
Systems…(continued)
Clients perform
presentation
functions
USER
B
USER
A
USER
C
NETWORK
Database
server runs
the DBMS
and performs
database
functions
DATABASE
Application
server performs
business
functions
DATABASE
SERVER
APPLICATION
SERVER
Three-tier client/server
architecture
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Advantages of Client/Server
Systems…
• Lower Network Traffic. A client/server system transmits only the
necessary data, rather than entire files, across the network.
• Improved Processing Distribution. Let you distribute processing
functions among multiple computers.
• Thinner Clients. Because the application and database server
handle most of the processing in a client/server system, clients do
not need to be as powerful or as expensive as the would in a fileserver environment.
• Greater Processing Transparency. As far as a user is concerned, all
processing occurs on the client just as it does on a stand-alone
system. Users do not need to learn any special commands or
techniques to work in a client/server environment.
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Advantages of Client/Server
Systems…(continued)
• Increased Network, Hardware, and Software Transparency. A
single operation could access data from different networks,
different computers, and different OS.
• Improved Security. In addition to security features of DBMS on
database server, you can place additional security features on the
application servers and on the network.
• Decreased Cost. Client/server
systems have proven to be powerful
enough that organizations have replaced, at a considerable cost
savings, enterprise applications and mainframe databases with PC
applications and database managed by client/server systems.
• Increased Scalability. If an application server or database server
becomes a bottleneck, you can upgrade the appropriate server or
add additional processors to share the processing load.
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Distributed Database
Is a single logical database that is physically divided among
computers at several sites on a network.
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Property of Distributed DBMSs
(DDBMS)…
• Homogeneous DDBMS is one that has the same local DBMS at
each site.
• Heterogeneous DDBMS is one that does not; there are at least
two sites at which the local DBMSs are different.
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Characteristics of Distributed
DBMSs (DDBMS)…
• Location Transparency
• Replication Transparency
• Fragmentation Transparency
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Advantages of Distributed
Database…
• Local control of data
• Increasing database capacity
• System availability
• Improved performance
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Disadvantages of Distributed
Database…(continued)
• Update of replicated data
• More complex query processing
• More complex treatment of concurrent update
• More complex recovery measures
• More difficult management of the data dictionary
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Advantages of Distributed
Database…(continued)
• More complex database design
• More complicated security and backup requirements
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Rules for Distributed Databases
• Local autonomy
• No reliance on a central site
• Continuous operation
• Location transparency
• Fragmentation transparency
• Replication transparency
• Distributed query processing
• Distributed transaction management
• Hardware independence
• Operating system independence
• Network Independence
• DBMS independence
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