BACS 485
Multi-User Database
Processing
Lecture Objectives
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
Learn the difference between single and
multi-user database processing and
understand the importance of multiuser issues
Learn the different system architectures
that can be used to support multi-user
database processing and the pros and
cons of each.
Teleprocessing Systems

The classic mode of supporting multiusers.





One computer
One CPU
“dumb” terminals
classic “time sharing” setup
bandwidth limitations cause interface to be
primitive (text based)
Teleprocessing Systems
AP1
Terminal 1
Terminal 2
OS cc
AP2
DBMS
Terminal n
AP3
Teleprocessing Computer
OS dm
DB
Client-Server Architecture

Client-server involves several computers
(at least 2)

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applications shifted to the client
all computers connected in a network
the ‘server’ provides a service, the ‘client’
uses the service
multiple servers are possible, but each
must process a single database to be
considered “client-server”.
Client-Server Architecture
User 1
AP1
OS net
Local Area Network
AP2
Client 1 Computer
User 2
AP2
OS net
OS net
DBMS OS dm
Client 2 Computer
Database Server
Computer
AP2
User n
OS net
AP3
Client N Computer
DB
File-Sharing Architecture

File-sharing distributes applications and
DBMS to user computers.


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the “server” provides access to files only
older and more primitive than client-server
typically involves more file transfer
overhead
files locks during transfer limit usefulness
as a transaction processing system
useful for group of large read-only files
File-Sharing Architecture
AP1
DBMS
User 1
OS net
Local Area Network
AP2
Computer 1
User 2
AP2
DBMS
OS net
OS net
OS dm
Computer 2
File Server
Computer
AP2
User n
DBMS
OS net
AP3
Computer 3
DB
Distributed Database
Architecture

The database itself is distributed


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the logical database is physically spread
across several computers
requires a distributed database
management system (DDBMS)
each computer can process requests to its
portion of the data and can request data
from other nodes
all this is transparent to the user
note the difference between distributed
processing and distributed database.
Distributed Database
Architecture
OS net
AP1
DDBMS
User 1
DB
AP2
OS dm
Logical
Database
Computer 1
OS net
User 2
DB
DDBMS
OS dm
Computer 2
Network
OS net
AP2
User n
DDBMS
AP3
DB
OS dm
Computer N
Types of Distributed
Databases

There are 4 basic combinations of
distributed database:
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Nonparatitioned, Nonreplicated
Partitioned, Nonreplicated
Nonpartitioned, Replicated
Partitioned, Replicated
These can be applied in a variety of
ways causing a continuum of choices.
Non-Partitioned
Non-Replicated Database
AP1
AP2
W
X
Y
Z
DBMS/OS
Single Processing
Computer
Partitioned Non-Replicated
Database
Communication Line
AP1
DDBMS/
OS
W
X
DB1
Computer 1
AP2
DDBMS/
OS
Computer 2
Y
Z
DB2
Logical Database
Non-Partitioned Replicated
Database
AP1
AP2
Communication Line
DDBMS/
OS
Computer 1
AP1
AP2
DDBMS/
OS
Computer 2
W
X
Y
Z
DB
(copy 1)
W
X
Y
Z
DB
(copy 2)
Partitioned Replicated
Database
Communication Line
AP1
W
DDBMS/
OS
X
Computer 1
DB1
AP2
DDBMS/
OS
Computer 2
Y
Y
Z
DB2
Logical Database
Continuum of Distributed
Alternatives
Unified
Database
Single
Nonpartitioned
Nonreplicated
Continuum
Partitioned
Nonreplicated
Nonpartitioned
Replicated
Distributed
Databases
Partitioned
Replicated
Increasing Parallelism
Increasing Independence
Increasing Flexibility
Increasing Availability
Increasing Cost/Complexity
Increasing Difficulty of Control
Increasing Security Risk
These last
3 are
negatives