1. April 4, 2002 Updating XML Views of Relational Data 1 Master’s Thesis Update Talk For Mukesh Mulchandani Advisor : Prof. Elke Rundensteiner Reader : Prof. George Heineman

2. April 4, 2002 Updating XML Views of Relational Data 2 Outline Motivation Background Material Rainbow System My Extension to Rainbow System Work in Literature Assumptions and Restrictions Approach Status Evaluation Related Work

3. April 4, 2002 Updating XML Views of Relational Data 3 Motivation XML is here to stay … –Universal representation of data –De facto standard for information exchange But RDBMS is mature –Mature query optimization techniques –High query performance Hence Extensive research on storing XML into RDBs and publishing XML –Florescu and Kossman, Storing and Querying XML Data Using RDBMS, In Bulletin of Technical Committee on Data Engineering, 1999 –Shanmugasundaram, He, Tufte, Zhang, DeWitt and Naughton, Relational Databases for Querying XML Documents : Limitations and Opportunities, VLDB 1999 –Zhang, Lee, Mitchell and Rundensteiner, Clock: Synchronizing Internal Relational Storage with External XML Documents, RIDE-DM 2000

4. April 4, 2002 Updating XML Views of Relational Data 4 Bridging XML & RDBs Relations RDBMS Default XML View XML Virtual View XQuery XPERANTO & Rainbow XQuery to Query Translation Query Composition Query Rewriting Computation Pushdown SQL Generation Updates ? – Not yet supported XML Documents SQL Query Executor Tuples

5. April 4, 2002 Updating XML Views of Relational Data 5 My Thesis Goals Specify updates on XML views Push updates correctly into underlying relations –Irrespective of mapping chosen between XML to RDB  Issues to be addressed: –How to specify updates ? –What kind of updates? –Meaning of updates at RDB end (Schema or Data Updates) –How to propagate ? –How to know that propagation is correct ? –How is the performance ?

6. April 4, 2002 Updating XML Views of Relational Data 6 Outline Motivation Background Material Rainbow System My Extension to Rainbow System Work in Literature Assumptions and Restrictions Approach Status Evaluation Related Work

7. April 4, 2002 Updating XML Views of Relational Data 7 Example of XML document & XQuery Michael Savitch Data Structures in C++ 2000 Peter Naughton JAVA 2 Reference 1998 User XQuery: FOR $author IN document(“authorview”)/author WHERE $author/last = “Savitch” RETURN $author/title Result : Data Structures in C++

8. April 4, 2002 Updating XML Views of Relational Data 8 XML views of Relational Data Michael Savitch 1 Peter Naughton 2 1 Data Structures in C++ 2000 2 JAVA 2 Reference 1998 FirstLastBookId MichaelSavitch1 PeterNaughton2 Author BookIdTitleYear 1Data Structures in C++2000 2JAVA 2 Reference1998 Book Default View

9. April 4, 2002 Updating XML Views of Relational Data 9 XML views of Relational Data (Contd) Michael Savitch Data Structures in C++ 2000 Peter Naughton JAVA 2 Reference 1998 Mapping View FOR $authortuple IN document(“Default.xml”)/author/row $booktuple IN document(“Default.xml”)/book/row WHERE $authortuple/bookid = $booktuple/bookid RETURN $authortuple/first $authortuple/last $booktuple/title $booktuple/year

10. April 4, 2002 Updating XML Views of Relational Data 10 Outline Motivation Background Material Rainbow System My Extension to Rainbow System Work in Literature Assumptions and Restrictions Approach Status Evaluation Related Work

11. April 4, 2002 Updating XML Views of Relational Data 11 Rainbow Query Engine View Composition SQL Generator RDBMS XAT User Query XQuery SQL Kweelt XQuery Parser XAT Executor User Query Results in XML Tuples XAT Rewrite XAT Mapping Query XAT Generator XML View Manager Parsed Tree Mapping Query Default Schema

12. April 4, 2002 Updating XML Views of Relational Data 12 What Changes Do I Need To Make ? Extend : –XQuery language to support XML Updates –XQuery Parser (Kweelt) to parse updates –“XAT Generator” to generate update nodes in XAT Add Functionality: –“View Analyzer” to extract knowledge of underlying tables and relationships among them. –“Update Decomposer” to decompose given XML update into relational updates –“Update Translator" to make correct SQL translation using semantic information about relational tables.

13. April 4, 2002 Updating XML Views of Relational Data 13 XAT Rewrite View Composer Update Manager within Rainbow RDBMS User Update Tuples View Analyzer Update Decomposer XAT Update Translator Single Table Updates Table Relationships Multiple SQL updates SQL Node Generation User Query SQL XAT Executor User Query Results in XML XAT Generator SI Kweelt XQuery Parser Mapping Query Default Schema Mapping Query XML View Manager Update Parser XAT Parsed Tree

14. April 4, 2002 Updating XML Views of Relational Data 14 Outline Motivation Background Material Rainbow System My Extension to Rainbow System Work in Literature Assumptions and Restrictions Approach Status Evaluation Related Work

15. April 4, 2002 Updating XML Views of Relational Data 15 Relational View Update Scenario FirstLastBookId MichaelSavitch1 PeterNaughton2 Author BookIdTitleYear 1Data Structures in C++2000 2JAVA 2 Reference1998 Book FirstLastTitleYear MichaelSavitchData Structures in C++2000 PeterNaughtonJAVA 2 Reference1998 AuthorView Root Table Ownership or Subset Relationships Reference Relationships

16. April 4, 2002 Updating XML Views of Relational Data 16 Work appeared in Literature On the updatability of relational views –Dayal and Bernstein – IEEE transaction 1978 A Relational Database View Update Translation Mechanism –Yoshifumi Masunaga – VLDB 1984 Algorithms for translating view updates to database updates for view involving selections, projections, and joins. –A. M. Keller ACM SIGACT-SIGMOD 1985 Updating Relational Databases through Object-Based Views –A. M. Keller, Barsalou, Siambela and Wiederhold – SIGMOD 1991

17. April 4, 2002 Updating XML Views of Relational Data 17 Root Relation –A relational table under the view –Key of the view elements is same as the key of this relation Term Definitions (Keller – SIGMOD 1991) Michael Savitch Data Structures in C++ 2000 Peter Naughton JAVA 2 Reference 1998 FirstLastBookId MichaelSavitch1 PeterNaughton2 Author (Key : (First,Last)) BookIdTitleYear 1Data Structures in C++2000 2JAVA 2 Reference1998 Book (Key : Bookid) Root

18. April 4, 2002 Updating XML Views of Relational Data 18 1SavitchMichael 2NaughtonPeter BookIdLastFirst Author (Key : (First,Last)) 2000Data Structures in C++1 JAVA 2 Reference Title 19982 YearBookId Book (Key : Bookid) Term Definitions (Contd.) Ownership Connection (R2 is owned by R1) –Foreign key (also part of key) of R2, not unique, referring to key of R1 (1 : n) Subset Connection (R2 is subset of R1) –Foreign key (also key) of R2, unique, referring to key of R1 (1:1) Reference Connection (R2 References R1) –Foreign key of R2, null allowed, not unique, referring to key of R1.

19. April 4, 2002 Updating XML Views of Relational Data 19 Term Definitions (Contd.) Dependency island of view –Maximal sub-tree of the tree of projections such that Root of sub-tree is root relation All directed paths beginning at root relation contain exclusively ownership and subset connections Referencing Peninsula –Is a relation directly connected to any relation of dependency island Via reference connection

20. April 4, 2002 Updating XML Views of Relational Data 20 Outline Motivation Background Material Rainbow System My Extension to Rainbow System Work in Literature Assumptions and Restrictions Approach Status Evaluation Related Work

21. April 4, 2002 Updating XML Views of Relational Data 21 Restrictions on views View should be in SPJ form –Only select, project and joins are allowed in view definition View has at least one root relation –Key of table is also key of XML elements in view No Aggregation in view definition –No aggregate columns such as max( ), count( ) etc No explicit external dependencies –No element value computed from values of other elements

22. April 4, 2002 Updating XML Views of Relational Data 22 Assumptions for type of updates Only data updates are performed Only complete valid updates are issued Michael Savitch Data Structures in C++ 2000 Peter Naughton JAVA 2 Reference 1998 FOR $root IN document(“authorview.xml”) $author IN $root/author[first = “Michael”][last = “Savitch”] UPDATE $root{ DELETE $author } FOR $root IN document(“authorview.xml”) UPDATE $root{ INSERT Joe Smith First Book 2002 }

23. April 4, 2002 Updating XML Views of Relational Data 23 Outline Motivation Background Material Rainbow System My Extension to Rainbow System Work in Literature Assumptions and Restrictions Approach Status Evaluation Related Work

24. April 4, 2002 Updating XML Views of Relational Data 24 XQuery Update Grammar FOR $binding1 IN Xpath-expr,….. LET $binding := Xpath-expr,… WHERE predicate1,….. updateOp,…… Where updateOp is defined as : UPDATE $binding {subOp {, subOp}* } and subOp is : DELETE $child | RENAME $child To new_name | INSERT ( $bind [BEFORE | AFTER $child] | new_attribute(name, value) | new_ref(name, value) | content [BEFORE | AFTER $child] ) | REPLACE $child WITH ( new_attribute(name, value) | new_ref(name, value) | content ) | FOR $sub_binding IN Xpath-subexpr,….. WHERE predicate1,………. updateOp. A FLWU Expression

25. April 4, 2002 Updating XML Views of Relational Data 25 FOR $authortuple IN document(“Default.xml”)/author/row $booktuple IN document(“Default.xml”)/book/row WHERE $authortuple/bookid = $booktuple/bookid RETURN $authortuple/first $authortuple/last $booktuple/title $booktuple/year Running Example Michael Savitch Data Structures in C++ 2000 Peter Naughton JAVA 2 Reference 1998 FOR $root IN document(“authorview.xml”) $author IN $root/author[first = “Michael”][last = “Savitch”] UPDATE $root{ DELETE $author } Mapping View User Update Expected Effect Peter Naughton JAVA 2 Reference 1998 Mapping Query

26. April 4, 2002 Updating XML Views of Relational Data 26 My Approach Analyze mapping query XAT to find –underlying relations –root relation for the view –relationship of other relations with root relation Generate XAT for user update on mapping view Massage composed tree to decompose update into updates against individual relations Use semantic information for correct translation of updates Generate SQL updates executed in the relational engine.

27. April 4, 2002 Updating XML Views of Relational Data 27 Step 1 : Analysis of mapping query XAT S(“Default.xml”):S1  (S1, /author/row):$authortuple  ($authortuple, bookid):$col1 S(“Default.xml”):S1  (S2, /book/row):$booktuple  ($bookuple, bookid):$col2  ($col1=$col2)  ($authortuple, first):$col3  ($authortuple, last):$col4  ($booktuple, title):$col5  ($booktuple, year):$col6 T ( [$col3], [$col4], [$col5], [$col6] ):col7 T( [col7] ):col8 Agg()  Root Relation : Author Dependency Island : Author Referencing Peninsulas : None ……… ……. …… …….. Relations : Author, Book Database Catalog Author : First, Last Book : Bookid FOR $authortuple IN document(“Default.xml”)/author/row $booktuple IN document(“Default.xml”)/book/row WHERE $authortuple/bookid = $booktuple/bookid RETURN $authortuple/first $authortuple/last $booktuple/title $booktuple/year

28. April 4, 2002 Updating XML Views of Relational Data 28 Step 2 : Generation of XAT for user update FOR $root IN document(“authorview.xml”) $author IN $root/author[first = “Michael”][last = “Savitch”] UPDATE $root{ DELETE $author } S(“authorview.xml”):S1  (S1, ):$root  ($col1=“ Michael”)  ($root, author):$author  ($author, first):$col1  ($author, last):$col2  ($col2=“ Savitch”):$author Delete($root, $author)

29. April 4, 2002 Updating XML Views of Relational Data 29 Composing two XATs S(“Default.xml”):S1  (S1, /author/row):$authortuple  ($authortuple, bookid):$col1 S(“Default.xml”):S2  (S2, /book/row):$booktuple  ($bookuple, bookid):$col2  ($col1=$col2)  ($authortuple, first):$col3  ($authortuple, last):$col4  ($booktuple, title):$col5  ($booktuple, year):$col6 T ( [$col3], [$col4], [$col5], [$col6] ):col7 T( [col7] ):col8 Agg()  S(“authorview.xml”):S1  (S1, ):$root  ($col1=“ Michael”)  ($root, author):$author  ($author, first):$col1  ($author, last):$col2  ($col2=“ Savitch”):$author Delete($root, $author)

30. April 4, 2002 Updating XML Views of Relational Data 30 Composed Algebra Tree  ($col3=“ Michael”)  ($author, first):$col3  ($author, last):$col4  ($col4=“ Savitch”):$author Delete($root, $author) S(“Default.xml”):S1  (S1, /author/row):$authortuple  ($authortuple, bookid):$col1 S(“Default.xml”):S2  (S2, /book/row):$booktuple  ($bookuple, bookid):$col2  ($col1=$col2):$root 

31. April 4, 2002 Updating XML Views of Relational Data 31 Step 3 : Decomposing the Update  ($col3=“ Michael”)  ($author, first):$col3  ($author, last):$col4  ($col4=“ Savitch”):$author Delete($root, $author) S(“Default.xml”):S1  (S1, /author/row):$authortuple  ($authortuple, bookid):$col1 S(“Default.xml”):S2  (S2, /book/row):$booktuple  ($bookuple, bookid):$col2  ($col1=$col2):$root 

32. April 4, 2002 Updating XML Views of Relational Data 32 Decomposing the Update (Contd.) Delete(author, first = “Michael”, last = “Savitch”, Bookid = book.Bookid) Delete(book, Bookid = author.Bookid author.first = “Michael” author.last = “Savitch”) Delete($root, $author) S(“Default.xml”):S1  (S1, /author/row):$authortuple  ($authortuple, bookid):$col1 S(“Default.xml”):S2  (S2, /book/row):$booktuple  ($bookuple, bookid):$col2  Delete($root, $author) S(“Default.xml”):S1  (S1, /author/row):$authortuple  ($authortuple, bookid):$col1 S(“Default.xml”):S2  (S2, /book/row):$booktuple  ($bookuple, bookid):$col2 

33. April 4, 2002 Updating XML Views of Relational Data 33 Step 4 :Correct Translation of Update Delete Algorithm (A. M. Keller, SIGMOD 1991) –Isolate Dependency island –For each projection in dependency island, delete all matching tuples from underlying relation –Identify referencing peninsulas –For each peninsula, perform a replacement on the foreign key of each matching tuple Delete(author, first = “Michael”, last = “Savitch”, Bookid = book.Bookid) Delete(book, Bookid = author.Bookid author.first = “Michael” author.last = “Savitch”) Root Relation : Author Dependency Island : Author Referencing Peninsulas : None

34. April 4, 2002 Updating XML Views of Relational Data 34 Step 5 : Generation of SQL Update DELETE FROM author WHERE first = ‘Michael’ AND last = ‘Savitch’ AND bookid IN (SELECT bookid FROM book) Delete(author, first = “Michael”, last = “Savitch”, Bookid = book.Bookid)

35. April 4, 2002 Updating XML Views of Relational Data 35 Outline Motivation Background Material Rainbow System My Extension to Rainbow System Work in Literature Assumptions and Restrictions Approach Status Evaluation Related Work

36. April 4, 2002 Updating XML Views of Relational Data 36 Status XQuery to support updates on XML XQuery Parser (Kweelt) to parser updates “XAT Generator” to generate update nodes in XAT View Analyzer  Update Decomposer  Update Translator Implementation : Ongoing Evaluation : not done yet

37. April 4, 2002 Updating XML Views of Relational Data 37 Evaluation Correct propagation of the updates. –Manual check on view reconstructed from tables after update. Works irrespective of the mapping chosen to map XML documents into RDB. –Experiment with different mapping approaches. Time taken to propagate the update –using different views having different no. of underlying tables.

38. April 4, 2002 Updating XML Views of Relational Data 38 Expected Contributions XQuery support for XML updates –Work done with MQP group. Framework for correct propagation of XML updates to underlying relations. –Application of object based view updating strategy to XML views –First solution for updating XML views Implementation of the system as a proof of concept & incorporate into full working system Rainbow Experimental evaluation.

39. April 4, 2002 Updating XML Views of Relational Data 39 Related Work Querying XML views of Relational Data –J. Shanmugasundaram, Jerry Kierman, Eugene Shekita, Catalina Fan and John Funderburk – VLDB 2001 Updating XML –Tatarinov, Ives, Alon Halevy and Daniel Weld SIGMOD 2001 Updating Relational Databases through Object-Based Views –A. M. Keller, Barsalou, Siambela and Wiederhold – SIGMOD 1991 Algorithms for translating view updates to database updates for view involving selections, projections, and joins. –A. M. Keller ACM SIGACT-SIGMOD 1985 A Relational Database View Update Translation Mechanism –Yoshifumi Masunaga – VLDB 1984 On the updatability of relational views –Dayal and Bernstein – IEEE transaction 1978