Incremental Maintenance for Materialized Views over Semistructured Data Written By: Serge Abiteboul...
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Transcript of Incremental Maintenance for Materialized Views over Semistructured Data Written By: Serge Abiteboul...
Incremental Maintenance for Materialized Views
over Semistructured Data
Written By: Serge Abiteboul Jason McHuge
Michael Rys Vasilis VassalosJanet L. Wiener
presented By: Galit Fridman
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 8
Lorel Query Language
Uses the select..from..where
clauses and additional clause with. Provides powerful path expressions
for traversing the data and rules.
Presented by: Galit Fridman 9
Standard Query
Example 1select efrom Guide.Restaurant r, r.Entree ewhere 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 2define view FavoriteEntrees as Entrees = select efrom Guide.Restaurant r, r.Entree ewhere 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 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.