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ByPaul Murray
Claire McQuadeKashif RafiqDavid Miller
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Introduction Federated Databases (FDBSs) Key areas
Characteristics of DBS/FDBS Architecture Views
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Characteristics - of DBS
• Distribution
• Autonomy
• Heterogeneity
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Characteristics - Autonomy
Autonomy
Logically Integrated Multiple DBMS
Federated DBMS
Multidatabase System
low High
Transaction Control
Query Processing
Distribution of ControlDegree to which individual DBMS can operate independently
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Characteristics-Distribution
Deals with data
Single DBS Many DBSs in a local area network Many DBSs in a wide area network
Distribution
Single DBS Multiple Sites
Local Distributed
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Characteristics-Distribution
Data and the Federated Database System (FDS) Databases may be on the same computer Databases may be geographically
separate Systems must be able to communicate
Benefits of distribution Improved access times Improved availability Improved reliability
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Characteristics -Heterogeneity Data models
Structures Constraints Query languages
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Characteristics of FDBS Collection of cooperating but autonomous
component database systems (DBSs)
Component DBSs integrated to various degrees
FDBMS Software that provides controlled and
coordinated manipulation of the component DBSs
No centralized control
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Types of FDBS
Multidatabase System
Loosely coupled
Federated DBSNonfederated DBS
Single Federation Multiple Federation
Tightly coupled
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Components of FDBS
Federated Database System
System 1 DBMS (centralised)
System 2 DBMS (distributed)
System N DBMS (FDBS)
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Architecture Processor Coupling Schemas
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Architecture - Processor Transforming Processors Filtering Processors Constructing Processors Accessing Processors
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Transforming Processors
SCHEMA A
TRANSFORMING PROCESSOR
SCHEMA B
Command TranslationSchema Translation
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Filtering Processors
SUBSET OF SCHEMA A
FILTERING PROCESSOR
SCHEMA A
Control CommandsControl Data
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Constructing Processors
SCHEMA A
CONSTRUCTING PROCESSOR
SCHEMA B SCHEMA C
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Accessing Processors
COMMANDS
ACCESSING PROCESSOR DATA
DATABASE
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Architecture - Coupling Loosely Coupled FDBS Tightly Coupled FDBS
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Architecture - Schema Schema Models
Five layer model Seven layer model Schema evolution
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Schema - Five-Level
Component DBS Component DBS
Local Schema
Component Schema
Export Schema Export Schema
Federated
Schema
ExternalSchema
Local Schema
Component Schema
Export Schema
Federated
Schema
ExternalSchema
External Schema
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Schema-Five-Level Processor
Component DBS
Local Schema
Component Schema
Export Schema
Federated
Schema
External Schema
Transforming Processor
Filtering Processor
Constructing Processor
Filtering Processor
Component DBS
Local Schema
Component Schema
Export Schema
Federated
Schema
External Schema
Transforming Processor
Filtering Processor
Constructing Processor
Filtering Processor
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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
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Semantic - Integrity Constraints 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
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Architecture - Views Selection Projection Join Real
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Conclusion