The TSIMMIS Approach to Mediation: Data Models and Languages

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The TSIMMIS Approach to Mediation Data Models
and Languages

• Hector Garcia-Molina
• Yannis Papakonstantinou
• Dallan Quass
• Anand Rajaraman

Yehoshua Sagiv Jeffrey Ullman Vasilis
Vassalos Jennifer Widom
Stanford University
Presented by Craig Parker for BYU CS652
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TSIMMIS The Problem

• There are many different sources of information.
• The format of the data in these sources may vary
  greatly.
• It is difficult to model the data when the
  original structures are so different.

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TSIMMIS The Solution

• The Stanford-IBM Manager of Multiple Information
  Sources (TSIMMIS)
• Offers
• A flexible data model
• A common query language
• Other supporting tools

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TSIMMIS Components

• OEM (Object-Exchange Model)
• MSL (Mediator Specification Language)
• Wrappers
• LOREL (Lightweight Object REpository Language)

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TSIMMIS OEM

• Object Exchange Model
• The data model for TSIMMIS
• self-describing (labels carry all of the
  information that there is about an object)
• Flexible
• First order logic

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TSIMMIS OEM
set or string
Object Identifier
type
value
OID
label
Human Understandable
A set or a string
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TSIMMIS OEM
library
set
book
set
author
string
Aho
title
string
Compilers
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TSIMMIS OEM
First order predicate logic
author
string
Aho
123
title( T, Aho )
This would return the object IDs of all objects
with a label title and value Aho.
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TSIMMIS MSL

• Mediator Specification Language
• Allows declarative specification of mediators
• Object oriented, logical query language
• Targeted to OEM

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TSIMMIS MSL
Query
Mediator
What is a mediator?
Mediator
Wrapper
Wrapper
Source
Source
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TSIMMIS MSL
An MSL Example
library
set
book
set
author
string
Aho
title
string
Compilers
ltbooktitle Xgt - ltlibrary ltbook lttitle Xgt
ltauthor Ahogt gt gt _at_s1
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TSIMMIS Wrappers

• What is a wrapper?

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TSIMMIS Wrappers
Query

• Wrappers are similar to database drivers
• Wrappers are written with MSL

Mediator
Mediator
Wrapper
Wrapper
Source
Source
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TSIMMIS Wrappers

• Wrappers have the form

MSL template // action //

• Example

ltbooks Xgt - ltlibrary Xltbook lttitle Xgt
ltauthor AUgtgt gt_at_s1 // sprintf(lookup-query,
find author s, AU) //
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TSIMMIS Wrappers

• Query Normalization
• Uses logical deduction to enhance the
  capabilities of the wrapper or mediator
• Examples
• Changing the order ANDed subconditions
• Transitive closure

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TSIMMIS LOREL

• Lightweight Object REpository Language
• An OQL for OEM
• The end-user language for TSIMMIS

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TSIMMIS LOREL

• Example

select library.book.title from library where
library.book.author Aho
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TSIMMIS LOREL

• Partial Match Semantics

select R.A from R, S, T where R.A S.A or R.A
T.A

• This would fail to return anything in SQL if
  either S or T were empty.
• Because of partial match semantics this does not
  fail in LOREL

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TSIMMIS Summary

• OEM is a flexible OO data model
• MSL can specify both mediators and wrappers
• Query normalization increases the power of
  mediators and wrappers
• LOREL is flexible and powerful