1. 1 Maintaining Semantics in the Design of Valid and Reversible SemiStructured Views Yabing Chen, Tok Wang Ling, Mong Li Lee Department of Computer Science National University of Singapore

2. 2 Outline Introduction Motivating Example Design Rules for Swap Operators Conclusion

3. 3 Introduction XML  The dominant standard for exchanging data on the Internet XML Views  Exploit the potential of XML  Secure the source data  Provide an application-specific view

4. 4 Related Work XML Views on Relational Database  SilkRoute [1] [2] Two different language to define and query the views over relational data  XPERANTO [3] [4] uses a canonical mapping to create a default XML view from relational data  ROLEX [14] Uses XSLT to define XML views. XML Views on XML Data  Xyleme [15] Define XML views using DTD  ActiveView [16] Define views with active features [1]M. Fernandez, W. Tan, D. Suciu, “Efficient Evaluation of XML Middleware Queries”, ACM SIGMOD, pp. 103-114, 2001. [2] M. Fernandez, W. Tan, D. Suciu, “SilkRoute: Trading Between Relations and XML”, World Wide Web Conference, 1999. [3] M. Carey, J. Kiernan, J. hanmugasundaram, et. al., “XPERANTO: A Middleware for Publishing Object-Relational Data as XML Documents”, VLDB, pp. 646-648, 2000. [4] M. Carey, D. Florescu, Z. Ives, et. al., “XPERANTO: Publishing Object-Relational Data as XML”, WebDB Workshop, 2000. [15] Sophie Cluet, Pieanglo Veltri, Dan Vodislav, Views in a large scale xml repository, VLDB 2001, pp. 271-280. [16] Serge Abiteboul, Sophie Cluet, Laurent Mignet, et. Al. Active views for electronic commerce, VLDB 1999, pp.138-149.

5. 5 Weakness of related work Disadvantage of the main related work  Ignore semantic information in source data For example, ignore the difference between object class, attribute and relationship in schema  Cannot check the validity of designed views  Difficult to use query languages to define views Proprietary language or XQuery

6. 6 Our approach Our approach for XML views  Our previous work Design valid XML Views [9]  Based on a semantically rich model - ORA-SS [18]  Use query operators, such as selection, drop, swap, join, etc.  Our current work (this paper) A complete set of rules for swap operators & reversible views Maintain participation constraints for relationship types in the views. [9] Ya Bing. Chen, Tok Wang Ling, Mong Li Lee, “Designing Valid XML Views”, ER Conference, 2002 [18] Gillian Dobbie, Xiao Ying Wu, Tok Wang Ling, Mong Li Lee, ORA-SS: An Object-Relationship-Attribute Model for SemiStructured Data, Technical Report TR21/00, School of Computing, National University of Singapore, 2000.

7. 7 Motivating Example ORA-SS data model  Object class – Rectangle  Attribute – circle  Relationship type – label on the connection between object classes Difference between ORA-SS and ER diagram  ORA-SS is hierarchical structure  ER is flat structure Difference between ORA-SS and other XML models  More semantics expressed. i.e. differentiate object class and attribute, differentiate the relationship attributes and object class attributes

8. 8 Motivating Example (cont.) Invalid view may be created by swapping course & student incorrectly  Relationship attribute grade relocated wrongly.  Relationship type cl disappears. Swap course & student Source Schema Invalid view Schema

9. 9 Motivating Example (cont.) Fortunately, valid view can be created based on our developed rules.  Relationship attribute grade relocated correctly.  Relationship type cl is kept in the view correctly. Swap course & student Source Schema Valid view Schema

10. 10 Swap Operators Our previous work  Select, join and drop operator.  Simple rules for swap operator Our current work  Detailed and complete rules for swap operator  Reversible views A view is reversible if its source schema can be produced back by applying swap operator on the view

11. 11 Swap Operator (cont.) Rule Swap_1: move attributes of O i and O j with O i and O j Swap O i & O j Reversible by applying the same rule

12. 12 Swap Operator (cont.) Relationship types affected: The path from Oj up to Oi and its ascendants The path involving Oi and its branch object class The path involving Oj and its descendants

13. 13 Swap Operator (cont.) Rule Swap_2: handles the first category of relationship types  Attach attributes of R at the lowest object class  Reason: keep the relationship attributes meaningful in the view Property of first category of relationship types:  The path from O j up to O i and its ascendants Swap O i & O j Reversible by applying the same rule

14. 14 Swap Operator (cont.) Rule Swap_3: handles the second category of relationship types  Attach sub trees of O i or O a to O i  Reason: keep the relationship meaningful in the view Property of the second category of relationship types:  The path involving O i and its branch object classes Swap O i & O j Reversible by applying the Rule Swap_4

15. 15 Swap Operator (cont.) Rule Swap_4: handle the third category of relationship types  Move sub trees of O j accordingly  Reason: keep the relationship meaningful in the view Property of the third category of relationship types:  The path involving O j and its descendants Swap O i & O j Reversible by applying the Rule Swap_3 & 4

16. 16 Conclusion An approach to maintaining semantics in designing views  A complete set of rules for the swap operator  Keep the relationship types correct in the views  Maintain the view reversibility The first work to maintain semantics (i.e. relationship types) Provide for a more robust view mechanism to guarantee the valid views design

17. 17 Thanks!

18. 18 References 1. Serge. Abiteboul, S. Cluet, L. Mignet, et. al., “Active views for electronic commerce”, VLDB, pp.138-149, 1999. 2. Chaitanya. Baru, A. Gupta, B. Ludaescher, et. al., “XML-Based Information Mediation with MIX”, ACM SIGMOD Demo, 1999. 3. Michael. Carey, J. Kiernan, J. hanmugasundaram, et. al., “XPERANTO: A Middleware for Publishing Object- Relational Data as XML Documents”, VLDB, pp. 646-648, 2000. 4. Michael. Carey, D. Florescu, Z. Ives, et. al., “XPERANTO: Publishing Object-Relational Data as XML”, WebDB Workshop, 2000. 5. Ya Bing. Chen, Tok Wang Ling, Mong Li Lee, “Designing Valid XML Views”, ER Conference, 2002 6. Ya Bing Chen, Tok Wang Ling, Mong Li Lee, “Automatic Generation of SQLX Definitions from ORA-SS Views”, DASFAA, 2004. 7. Sophie. Cluet, P. Veltri, D. Vodislav, “Views in a large scale xml repository”, VLDB, pp. 271-280, 2001. 8. Gillian. Dobbie, X.Y Wu, T.W Ling, M.L Lee, “ORA-SS: An Object-Relationship-Attribute Model for SemiStructured Data”, Technical Report TR21/00, School of Computing, National University of Singapore, 2000. 9. Mary. Fernandez, W. Tan, D. Suciu, “Efficient Evaluation of XML Middleware Queries”, ACM SIGMOD, pp. 103-114, 2001. 10. Mary. Fernandez, W. Tan, D. Suciu, “SilkRoute: Trading Between Relations and XML”, World Wide Web Conference, 1999. 11. Philip. Bohannon, H. Korth, P. Narayan, S. Ganguly, and P. Shenoy. Optimizing view queries in ROLEX to support navigable tree results. VLDB, 2002. 12. Alin. Deutsch and V. Tannen. MARS: A System for Publishing XML from Mixed and Redundant Storage. VLDB, 2003.