Download Schema

By
Paul Murray
Claire McQuade
Kashif Rafiq
David Miller
1
Introduction
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
Federated Databases (FDBSs)
Key areas
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Characteristics of DBS/FDBS
Architecture
Views
2
Characteristics - of DBS
• Distribution
• Autonomy
• Heterogeneity
3
Characteristics - Autonomy

Transaction Control

Query Processing

Distribution of Control
Degree to which individual DBMS can operate
independently
Logically
Integrated
Multiple DBMS
low
Federated
DBMS
Autonomy
Multidatabase
System
High
4
Characteristics-Distribution

Deals with data
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Single DBS
Many DBSs in a local area network
Many DBSs in a wide area network
Multiple Sites
Single DBS
Local
Distribution
Distributed
5
Characteristics-Distribution
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Data and the Federated Database
System (FDS)

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Databases may be on the same computer
Databases may be geographically separate
Systems must be able to communicate
Benefits of distribution
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Improved access times
Improved availability
Improved reliability
6
Characteristics -Heterogeneity
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Data models
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Structures
Constraints
Query languages
7
Characteristics of FDBS
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Collection of cooperating but autonomous
component database systems (DBSs)
Component DBSs integrated to various
degrees
FDBMS

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Software that provides controlled and coordinated
manipulation of the component DBSs
No centralized control
8
Types of FDBS
Multidatabase System
Nonfederated DBS
Federated DBS
Loosely coupled
Tightly coupled
Single Federation
Multiple Federation
9
Components of FDBS
Federated Database System
System 1
System 2
System N
DBMS (centralised)
DBMS (distributed)
DBMS (FDBS)
10
Architecture

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Processor
Coupling
Schemas
11
Architecture - Processor
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Transforming Processors
Filtering Processors
Constructing Processors
Accessing Processors
12
Transforming Processors
SCHEMA A
TRANSFORMING PROCESSOR
Command Translation
Schema Translation
SCHEMA B
13
Filtering Processors
SUBSET OF SCHEMA A
FILTERING PROCESSOR
Control Commands
Control Data
SCHEMA A
14
Constructing Processors
SCHEMA A
CONSTRUCTING PROCESSOR
SCHEMA B
SCHEMA C
15
Accessing Processors
COMMANDS
ACCESSING PROCESSOR
DATA
DATABASE
16
Architecture - Coupling
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Loosely Coupled FDBS
Tightly Coupled FDBS
17
Architecture - Schema
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Schema Models
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Five layer model
Seven layer model
Schema evolution
18
Schema - Five-Level
External
Schema
Export Schema
External
Schema
External
Schema
Federated
Federated
Schema
Schema
Export Schema
Export Schema
Component Schema
Component Schema
Local Schema
Local Schema
Component DBS
Component DBS
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Schema-Five-Level Processor
External Schema
External Schema
Filtering Processor
Filtering Processor
Federated
Federated
Schema
Schema
Constructing Processor
Constructing Processor
Export Schema
Export Schema
Filtering Processor
Filtering Processor
Component Schema
Component Schema
Transforming Processor
Transforming Processor
Local Schema
Local Schema
Component DBS
Component DBS
20
Schema - Evolution

One of the problems found with
federated databases is the cumulative
schema evolution rate

A client application cannot be tied to a
specific integrated view of the federation,
as all it takes is one member of the
federation to change its schema without
ensuring backward compatibility to cause
serious problems
21
Semantic - Integrity
Constraints
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The federated database schema should
correctly reflect the semantics of the
component database schemata of which
it is composed
Since the semantics of a database
schema is also determined by a set of
semantic integrity constraints, a correct
schema integration has to deal with
integrity constraints existing in the
different component database schemata
22
Architecture - Views
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Selection
Projection
Join
Real
23
Conclusion
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