Federated Database Systems

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Federated Database Systems

• -Archana Meka
• Ravi Kanth Kolli

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What is Data Integration?

• The problem of combining data residing at
  different sources and providing the user with a
  unified view of these data.
• Started around 1960s

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Federated Databases

• Transparently integrates multiple autonomous
  database systems into a single federation
• Coined by Heimbigner and McLeod (1985)
• Pros
• A component DBS can continue its local
  operations and participate in the federation

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Approaches for Federation

• Global View Integration
• Multi Database Language Approach
• Mediated Query Systems
• Ontology Driven Approach

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Ontology driven approach

• All the databases are first converted to a common
  model for easy access
• Uses ontologies as a common interface for all the
  databases
• Queries

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Process

• Find ontologies related to databases
• Develop ontologies
• Extending ontologies, merging
• Matching
• Add mappings
• Query Languages

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Step 1

• Reusing resources
• Checking if there are ontologies that are in the
  similar domain as the database
• Creating new ontologies
• New ontologies for databases

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Step 2

• Merging of ontologies
• Merging similar ontologies or a few smaller one
  into a single larger one
• Matching
• Different databases may have same concepts
• Matching between the schema of the ontologies

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Step 3

• Add mappings
• Mapping database schema and instances to
  ontologies
• Use Declarative Language for Mapping
• D2R mapping for RDBMS to RDF

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D2R Mapping

• Extract the record sets
• Record sets are grouped
• Create class instances and assigned a URI
• Instance properties are created

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Contd.
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Query

• Various methods
• Query database using the SQL or other database
  query language
• Query ontologies using SPARQL etc
• Provide an advanced GUI

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Few Systems

• The Garlic System
• Infoharness
• Infosleuth
• Observer

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The Garlic System
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Contd.

• Data repositories
• Includes relational, non-relational database
  systems, file systems, image managers
• Repository Wrapper
• Conversion of data from one format to the Garlic
  Format

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Contd.

• Metadata Repository
• Information on unified garlic schema, translation
  related information
• Complex Object Repository
• Complex objects that garlic application needs to
  combine the underlying data in new ways

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Contd.

• Query Processing and data manipulation
• Provides a unified object oriented view of the
  database for Garlic applications
• Queries are expressed in object oriented
  extension of SQL language
• C API that provides an interface to Garlic
  Applications

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Infoharness

• A metadata management system with a generic
  metadata storage system as its metabase
• Through 1993-1996
• Some of the research was commercialized as the
  AdaptX Harness platform, system and related
  services from Bellcore
•   InfoHarness is a trademark of Bellcore.

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InfoSleuth
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OBSERVER Global Architecture
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Observer

• Query Processor
• Takes as input a user query expressed in DL
  using terms from a chosen user Ontology
• Interontology Relationships Manager (IRM)
• Interontology relationships relating the terms in
  various ontologies
• Solution to vocabulary sharing problem

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• Ontology Server
• Provides information about the ontologies
  residing in the node
• Ontology
• It is a set of terms of interest in a particular
  information domain
• Semantically rich metadata capturing information
  content of underlying data repositories

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Problems

• Semantic Heterogeneity
• Query processor

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Semantic Heterogeneity

• Occurs when there is a disagreement about the
  meaning, interpretation or intended use of the
  same or related data

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References

• http//lsdis.cs.uga.edu/lib/download/105-InfoHarne
  ss.pdf -Infoharness
• http//www.almaden.ibm.com/cs/people/fagin/ride95.
  pdf -Garlic System