MDBS Schema Integration: The Relational Integration Model

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MDBS Schema Integration The Relational
Integration Model
Candidacy Exam Presentation for Ramon
Lawrence University of Manitoba umlawren_at_cs.umanit
oba.ca
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Outline

• Introduction
• The MDBS architecture and the Integration problem
• A schema integration taxonomy
• Previous Work
• The RIM Architecture and the RIM Model
• Future work and conclusions

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Database Terminology

• database system - a database and a system to
  manage the data
• transaction - an atomic sequence of operations
  applied to the database
• global transaction - a transaction spanning more
  than one database
• schema integration - the process of combining
  local schemas into a global, integrated schema
• multidatabase system (MDBS) - a collection of
  autonomous, local databases participating in a
  global database system to share data

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MDBS Architecture
Global Transactions

• Global Transaction Manager (GTM)
• processes global transactions
• insures information in all LDBSs is consistent
• submits subtransactions to the GTSs for each LDBS

GTM
subtransactions

• Global Transaction Servers (GTSs)
• one for each LDBS
• converts subtransactions from the GTM into a form
  usable by the LDBS and vice versa

• Local Database Systems (LDBSs)
• databases combined into MDBS
• unchanged as still process local transactions

Local Transactions
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The Integration Problem

• Integrating diverse data sources is an important
  issue as organizations interconnect their
  operations and demand more from their database
  systems
• Integration is a hard problem because structural
  and semantic conflicts exist
• Two levels of integration
• schema integration
• data integration

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Schema Integration

• Schema integration is the process of combining
  database schemas into a coherent global view
• Integration problems include
• different data models
• incompatible concept representations
• different user or view perspectives
• structural conflicts within a model
• naming conflicts (homonym, synonym)

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A Schema Integration Taxonomy
Automation Level
automatic (dynamic)
automatic (static)
semi-automatic
manual
Conflicts Resolved
interschema
all
naming
NONE
structural
semantic
structural
behavioral
both
Transparency
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Previous Work

• semantic models
• Batini (86), canonical models, SDM, DAPLEX
• schema re-engineering
• model mapping tools, schema transformations
• metadata systems
• rule-based systems
• object-oriented methods
• use as a canonical model, schema transformations
• application-level integration
• language systems, MSQL, IDL, higher order views

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Previous Work (cont.)

• Interdatabase dependencies
• Sheth - relaxed consistency, integration rules
• AI techniques
• Pegasus (spheres of knowledge), knowledge
  packets, Carnot project (Cyc knowledge base)
• Lexical semantics
• Summary Schemas Model (Bright et al.) - user
  interface for imprecise queries
• Industrial systems
• Interbase

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RIM Objective

• The objective of the RIM model is to provide a
  system for automatically integrating diverse
  relational schemas into a multidatabase
• Desirable properties
• individual mappings - information sources
  integrated one-at-a-time and independently
• global view constructed for query transparency
• handles schema conflicts - including semantic,
  structural, and naming conflicts
• automated global integration - global view
  constructed efficiently and automatically

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RIM The Idea

• The idea behind the RIM model is that most (and
  probably all) schema conflicts can be resolved if
  we
• eliminate all naming conflicts
• define a language capable of determining schema
  equivalence and performing transformations
• With these two properties, schema conflicts can
  be resolved automatically at the global level

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RIM The Plan

• The first task is eliminating naming conflicts
• use a global thesaurus/dictionary like SSM
• map local schema names into global counterparts
• identical concepts can be identified by global
  name
• The integration language must be defined
• RIM specifications - records capturing semantics
  of each LDBS in a machine-processable form
• global names captured in RIM specs. to identify
  concepts stored in LDBS

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RIM The Plan (cont.)

• Integrate RIM specifications
• To query the MDBS, the client downloads and
  integrates only RIM specs. of LDBSs accessed
• Global view is constructed from RIM specs. by
  automatically combining them at client site using
  global names and semantic metadata they contain
• Use of global names allows system to determine
  identical concepts even though structural
  representations may be different
• Semantic information captured using metadata

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RIM The Plan (cont.)

• Querying the MDBS
• queries are posed to the MDBS through the global
  view at each client
• translation from the GV back to the original RIM
  spec. for each LDBS is performed
• the translated queries are sent to each LDBS
  which transforms the query (specified using RIM)
  into a query for the LDBS
• results are returned to the client which
  integrates them based on its GV

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RIM Architecture

• RIM Specifications
• constructed at each RDBS
• local concepts mapped to global names
• schema can be automatically extracted

• RIM Integration
• uses needed RIM specs.
• constructs global view
• resolves conflicts by
• identifying concepts using global names
• transforming concepts into a form consistent
  with the global view

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RIM Using Global Names

• Global names attempt to capture semantics of data
  and its structure
• Research has found that a single dictionary term
  is insufficient to capture all semantics of a
  given data item
• Current proposed global name term
• context term concept name (adjective
  phrases)
• adjective phrase adjective preposition
  (context term or concept name)

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RIM Using Global Names (cont.)

• Here a few examples of using global names
• the database stores damage claim information
• Example 1
• attribute of claim is called net_amount in system
• GN Claim Net Amount
• Example 2
• attribute of claim is called claim_date in system
• GN1 Claim Claim date (received by system)
• GN2 Claim Claim date (received by company)
• GN3 Claim Claim date (submitted by claimant)

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RIM The Global Dictionary

• To match concepts across systems, a global
  dictionary is required. Global names are taken
  from this dictionary.
• Currently developing a simplified on-line
  dictionary
• stores hierarchy (IS-A) relationships and
  component (Part-of) relationships
• global terms for RIM are taken from the
  dictionary
• dictionary will allow user-defined words
• Future work involves determining how to add
  locally defined terms into the dictionary if
  required

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RIM Basic Concepts

• There are 3 basic modeling constructs in RIM
• entity - a concept whose existence does not
  depend on any other entities
• relationship - a combination of two or more
  entities which does not exists without them
• attribute - a characteristic of an entity or a
  relationship
• All entities and attributes should be
  identifiable by a global name from the dictionary.

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RIM RIM Specifications

• A RIM specification consists of two parts
• table headers - table-level information for each
  relation in database
• table schemas - information at the attribute
  level of a database relation
• Most of the information can be automatically
  extracted, however the DBA must assign global
  names to local concepts manually

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RIM The Table Header

• The table header provides table-level information
  for each relation and has fields
• name - unique table name (local)
• record size and count
• foreign key list and foreign key access list
• record insert/delete/update mechanisms
• record name - semantic name for a table record
• record type - entity, relationship instance, ...
• record grouping - why are records in the table?
• record distinction/duplicates - primary key
• table comment

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RIM The Table Schema

• The table schema contains attribute-level
  information. Some fields include
• field name - database system name
• semantic name - global name
• field use
• attribute, key, categorization, summation,
  date/time, foreign key, logical, numeric,
  reference

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RIM Semantic Conflicts

• There are 6 basic semantic conflicts in RIM
• attribute-entity conflict
• attribute-relationship conflict
• entity-relationship conflict
• entity-entity conflict (not studied)
• attribute-attribute conflict (not studied)
• relationship-relationship conflict (not studied)
• There is some basic ideas on how to automatically
  resolve the first 3 conflicts.
• Conflict resolution is an area of future work.

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Conclusions

• Current integration methodologies are
  insufficient because they rely on manual
  intervention and do not resolve all types of
  conflicts
• The RIM model may be able to integrate diverse
  relational schemas using a global dictionary, a
  systematic method for capturing data semantics,
  and automated procedures for performing client
  run-time integration

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Future Work

• Determining how the RIM specifications can be
  constructed and what information can be
  automatically extracted
• Deciding the format for the global dictionary
• Studying conflict resolution procedures and
  testing methodology on simple integration problems