Incremental Maintenance for Materialized Views over Semistructured Data

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. Outline • Introduction • Incremental Maintenance Approach • Definitions • Incremental Maintenance Algorithm • Evaluation • Conclusion Presented by: Galit Fridman

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

4. Introduction (cont.) • 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) Presented by: Galit Fridman

5. 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. Presented by: Galit Fridman

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

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

8. Lorel Query Language • Uses the select..from..whereclauses and additional clause with. • Provides powerful path expressions for traversing the data and rules. Presented by: Galit Fridman

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

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

11. View Specification • 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; Presented by: Galit Fridman

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

13. Update Operations • Insertion and deletions of the edge. Denoted: <Ins,o1,L,o2> <Del,o1,L,o2> • Change of value of the atomic object. Denoted: <Chg,o1,OldVal,NewVal> Presented by: Galit Fridman

14. Incremental Maintenance Algorithm Input 1. View specification statements. 2. Update U: <Ins,o1,L,o2>, <Del,o1,L,o2>, Chg,o1,Oldval,NewVal> 3. New database state DB’. 4. View instance V. Presented by: Galit Fridman

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

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

17. Database Size Presented by: Galit Fridman

18. Number of label occurrences Presented by: Galit Fridman

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

20. Bound Variable Position Presented by: Galit Fridman

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

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