1. Incremental Maintenance for Materialized Views over Semistructured Data Written By: Serge Abiteboul Jason McHuge Michael Rys Vasilis Vassalos Janet L. Wiener presented By: Galit Fridman

2. Presented by: Galit Fridman2 Outline l Introduction l Incremental Maintenance Approach l Definitions l Incremental Maintenance Algorithm l Evaluation l Conclusion

3. Presented by: Galit Fridman3 Introduction l Database views increase the flexibility of a database system. l Views are materialized to speed up querying, when the time is critical.

4. Presented by: Galit Fridman4 Introduction (cont.) l The view contents must be maintained in order to preserve consistency with the base data. Two ways: Recomputing the view contents from the database. Computing the incremental updates to the view, based on the updates to the database. (used by the new algorithm)

5. Presented by: Galit Fridman5 Incremental Maintenance Approach For nearly all types of database updates. It is more efficient to apply this algorithm to the view than recompute the view from the database.

6. Presented by: Galit Fridman6 The Algorithm is Based on: l OEM - Object Exchange Model l Lorel Query Language

7. Presented by: Galit Fridman7 OEM - Object Exchange Model

8. Presented by: Galit Fridman8 Lorel Query Language l Uses the select..from..where clauses and additional clause with. l Provides powerful path expressions for traversing the data and rules.

9. Presented by: Galit Fridman9 Standard Query l Example 1 select e from Guide.Restaurant r, r.Entree e where r.Name = “Baghdad Cafe” and e.Ingredient = “Mushroom” The answer is: {&9}

10. Presented by: Galit Fridman10 View Specification Statements l Identify objects within a graph. l Import arbitrary subgraphs. l Add or remove objects appearing in the view.

11. Presented by: Galit Fridman11 View Specification l Example 2 define view FavoriteEntrees as Entrees = select e from Guide.Restaurant r, r.Entree e where exists x in r.Name = “Baghdad Cafe” and exists y in e.Ingredient = “Mushroom” with e.Name n,e.Ingredient I;

12. Presented by: Galit Fridman12 Materialized Views l Primary objects- objects that are bound to e. l adjunct objects - subobjects discovered by the with clause.

13. Presented by: Galit Fridman13 Update Operations l Insertion and deletions of the edge. Denoted: l Change of value of the atomic object. Denoted:

14. Presented by: Galit Fridman14 Incremental Maintenance Algorithm Input 1. View specification statements. 2. Update U:,, Chg,o1,Oldval,NewVal> 3. New database state DB’. 4. View instance V.

15. Presented by: Galit Fridman15 Incremental Maintenance algorithm Basic Structure:

16. Presented by: Galit Fridman16 Base Cost For Update Operations

17. Presented by: Galit Fridman17 Database Size

18. Presented by: Galit Fridman18 Number of label occurrences

19. Presented by: Galit Fridman19 Length of the form clause

20. Presented by: Galit Fridman20 Bound Variable Position

21. Presented by: Galit Fridman21 Selectivity of the where clause

22. Presented by: Galit Fridman22 Conclusion l Advantage: The algorithm outperforms recomputation of the view, even for large numbers of insert and delete edge updates. Scales well with increasing the database. l Disadvantage: can be expensive as full recomputation of the view for a single atomic value change.