1. 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

2. 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.

3. TSIMMIS – The Solution The Stanford-IBM Manager of Multiple Information Sources (TSIMMIS) Offers: A flexible data model A common query language Other supporting tools

4. TSIMMIS – Components OEM (Object-Exchange Model) MSL (Mediator Specification Language) Wrappers LOREL (Lightweight Object REpository Language)

5. 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

6. TSIMMIS – OEM OID:label typevalue Object Identifier Human Understandable “set” or “string” A set or a string

7. TSIMMIS – OEM libraryset bookset authorstring titlestring Aho Compilers…

8. TSIMMIS – OEM First order predicate logic authorstringAho123 title( T, “Aho” ) This would return the object IDs of all objects with a label “title” and value “Aho”.

9. TSIMMIS – MSL Mediator Specification Language Allows declarative specification of mediators Object oriented, logical query language Targeted to OEM

10. TSIMMIS – MSL What is a mediator? Query Mediator Wrapper Source

11. TSIMMIS – MSL An MSL Example :- } > } > @s1 libraryset bookset authorstring titlestring Aho Compilers…

12. TSIMMIS – Wrappers What is a wrapper?

13. TSIMMIS – Wrappers Query Mediator Wrapper Source Wrappers are similar to database drivers Wrappers are written with MSL

14. TSIMMIS – Wrappers Wrappers have the form: MSL template // action // Example: :- }> }>@s1 // sprintf(lookup-query, “find author %s”, $AU) //

15. TSIMMIS – Wrappers Query Normalization Uses logical deduction to enhance the capabilities of the wrapper or mediator Examples:  Changing the order “AND”ed subconditions  Transitive closure

16. TSIMMIS – LOREL Lightweight Object REpository Language An OQL for OEM The end-user language for TSIMMIS

17. TSIMMIS – LOREL Example select library.book.title from library where library.book.author = “Aho”

18. 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

19. 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