incremental maintenance for materialized views over semistructured data

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


Introduction

Database views increase the flexibility of a database system.

Views are materialized to speed up querying, when the time is critical .


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)


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.


The Algorithm is Based on:

OEM - Object Exchange Model

Lorel Query Language


OEM - Object Exchange Model


Lorel Query Language

Uses the select..from..where

clauses and additional clause with. Provides powerful path expressions

for traversing the data and rules.


Standard Query

Example 1select efrom Guide.Restaurant r, r.Entree ewhere r.Name = “Baghdad Cafe”and e.Ingredient = “Mushroom”

The answer is: {&9}


View Specification Statements

Identify objects within a graph.

Import arbitrary subgraphs.

Add or remove objects appearing in the view.


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;


Materialized Views

Primary objects- objects that are bound to e.

adjunct objects - subobjects discovered by the with clause.


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>


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.


Incremental Maintenance algorithm

Basic Structure:


Base Cost For Update Operations


Database Size


Number of label occurrences


Length of the form clause


Bound Variable Position


Selectivity of the where clause


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.

incremental maintenance for materialized views over semistructured data

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