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

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Outline

• Introduction
• Incremental Maintenance Approach
• Definitions
• Incremental Maintenance Algorithm
• Evaluation
• Conclusion

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Introduction

• Database views increase the flexibility of a
  database system.
• Views are materialized to speed up querying, when
  the time is critical .

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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)

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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.

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The Algorithm is Based on

• OEM - Object Exchange Model
• Lorel Query Language

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OEM - Object Exchange Model
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Lorel Query Language

• Uses the select..from..where clauses and
  additional clause with.
• Provides powerful path expressions for traversing
  the data and rules.

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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

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View Specification Statements

• Identify objects within a graph.
• Import arbitrary subgraphs.
• Add or remove objects appearing in the view.

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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

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Materialized Views

• Primary objects- objects that are bound to e.
• adjunct objects - subobjects discovered by the
  with clause.

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Update Operations

• Insertion and deletions of the edge.
  Denoted ltIns,o1,L,o2gt
• ltDel,o1,L,o2gt
• Change of value of the atomic object.
• Denoted
• ltChg,o1,OldVal,NewValgt

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Incremental Maintenance Algorithm Input

• 1. View specification statements.
• 2. Update U ltIns,o1,L,o2gt,
• ltDel,o1,L,o2gt, Chg,o1,Oldval,NewValgt
• 3. New database state DB.
• 4. View instance V.

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Incremental Maintenance algorithm

• Basic Structure

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Base Cost For Update Operations
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Database Size
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Number of label occurrences
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Length of the form clause
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Bound Variable Position
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Selectivity of the where clause
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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.