Distributed Database Management Systems: Lecture 12

Distributed Database
Management Systems

Lecture 12


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

2


• GCSs in MDBS and logically
integrated DDBS is different
• Design process moves in inverse
directions, MDBS design process
is bottom up, where as in logically
integrated DDBS it is top-down

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Multidatabase Systems: Architectures
 External
Schema

 External
Schema

 External
Schema

 External
Schema

Federated
Schema

Global
Schema

Federated
Schema

Schema Integration
Export
Schema
Component
Schema

• • •

Export
Schema

Export

Schema

Export
Schema

Component
Schema
Component
Schema

• • •

Component
Schema

Schema Translation
Local
Schema

Local
Schema

• • •
Global Schema Architecture

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Local
Schema

Local
Schema

• • •
Federated Database Architecture
4


Global Data Dictionary

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• A directory is a database that
contains data about data (metadata)
• Called global directory in case of a
DDBS
• Contains mappings

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• A single large or multiple for
different sites
• Hierarchies of DD can be built
• Location: whether to keep at a

single site or distributed
• Single site increases load on that
site
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• Single copy or replication
• Replication increases availability
and reliability
• All three issues are orthogonal to
each other
• That concludes our Architecture
discussion
• Lets summarize
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Introduction
• Schema Design
The DDB Design concerns two
major steps, Schema Design and
Schema Distribution
• Schema Distribution
Distribution of Schema decides
the placement of data as well
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DDB Design
• Top-Down Design Process

• Bottom-Up Design Process

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Requirement Analysis
System Requirements (Objectives)
User Input

Conceptual Design

View Design

View Integration

Global Conceptual Schema

Access In formation External Schema Def.

Distributed Design
User Input

Local Conceptual Schemas
Physical Design
Physical Schema
Feedback

Feedback

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Observation and Monitoring

11


• Conceptual Design is Global
Conceptual Schema
• View Design results in individual
External Schema Definition
(Global users)
• Activities so far are similar to
Centralized DB Design
• Then start the distribution activity
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Bottom-Up Design
Process
 External

Schema

 External
Schema

Global
Schema

Component
Schema

Local
Schema

• • •

Component
Schema

Local
Schema

• • •
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Multidatabase Architecture 13


Distribution Design Issues

1. Why fragments

2. How should we
3. How much should be
fragmented
4. Any way to test correctness
5. Allocation Strategy
6. Required Information
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• Disadvantages:
– Difficult to manage in case of nonexclusive Fragmentation
(replication)
– Maintenance of Integrity constraints

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Thanks