Incremental maintenance for materialized views over semistructured data
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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. Outline. Introduction Incremental Maintenance Approach

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Incremental Maintenance for Materialized Views over Semistructured Data

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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


Outline

  • Introduction

  • Incremental Maintenance Approach

  • Definitions

  • Incremental Maintenance Algorithm

  • Evaluation

  • Conclusion

Presented by: Galit Fridman


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


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


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


The Algorithm is Based on:

  • OEM - Object Exchange Model

  • Lorel Query Language

Presented by: Galit Fridman


OEM - Object Exchange Model

Presented by: Galit Fridman


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


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


View Specification Statements

  • Identify objects within a graph.

  • Import arbitrary subgraphs.

  • Add or remove objects appearing in the view.

Presented by: Galit Fridman


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


Materialized Views

  • Primary objects- objects that are bound to e.

  • adjunct objects - subobjects discovered by the with clause.

Presented by: Galit Fridman


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


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


Incremental Maintenance algorithm

Basic Structure:

Presented by: Galit Fridman


Base Cost For Update Operations

Presented by: Galit Fridman


Database Size

Presented by: Galit Fridman


Number of label occurrences

Presented by: Galit Fridman


Length of the form clause

Presented by: Galit Fridman


Bound Variable Position

Presented by: Galit Fridman


Selectivity of the where clause

Presented by: Galit Fridman


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


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