Distributed Database Management Systems: Lecture 11

Distributed Database
Management System
Lecture 10


Major DDBS Architectures

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Client-Server Architecture
• Basic idea is to distribute
functionality
• Gives two level architecture
• The term used in different
meanings; generally C and S refer
to processes, may be running at
the same machines
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– As you can see in the figure
– Server performs most of the data
Management;
• Query Processing
• Transaction and Storage Management

– Client, mainly has
• application and user interface
• a client module of DBMS
• Data and lock management cached their
sometimes

– OS and Communication s/w
running at both
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• Client passes user queries to
server without trying to
understand or optimize them
• One Server Multiple Clients
• Multiple Servers
– One Server at a time
– Multiple Servers (transparently) at a
time

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Peer-to-Peer Distributed Systems

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ES1

ES2

ES1

ESn

GCS
LCS1

LCS2

LCSn

LIS1

LIS2

LISn

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• Physical data organization at
each site defining Local Internal
Schemas
• On top of that, Local Conceptual
Schema
• Then the overall view is depicted
by Global conceptual schema that
supports the External schemas
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•
•
•
•

Transparencies Supported
Extension of ANSI/SPARC Model
Data Independence supported
Local Data Dictionary and global
exist
• Both support local and global
mappings
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Interpreting user commands 
and formats results
Checks if user query can be 
processed
Optimized execution strategy
Global queries to local ones
Coordinates distribution 
execution of user requests

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Chooses best access path to 
any data item
Makes sure the consistency of 
local data even in case of 
failure
Physically accesses the data as 
per the commands generated 
by query optimizer. Interacts 
with the OS
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Major DDBS Architectures-III

A Multidatabase System

• Provides access from multiple,
autonomous heterogeneous, and
distributed databases. Two Major
architectures:
•
•

Global Schema Architecture
Federated Schema Architecture

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Global Schema Architecture
 G External
Schema

 G External
Schema

Global
Schema
Schema Integration

 L External
Schema

Component
Schema

• • •

Component
Schema

 L External
Schema
Schema Translation

Local
Schema

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• • •

Local
Schema

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