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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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Presented by: Galit Fridman2 Outline l Introduction l Incremental Maintenance Approach l Definitions l Incremental Maintenance Algorithm l Evaluation l Conclusion
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Presented by: Galit Fridman3 Introduction l Database views increase the flexibility of a database system. l Views are materialized to speed up querying, when the time is critical.
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Presented by: Galit Fridman4 Introduction (cont.) l 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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Presented by: Galit Fridman5 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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Presented by: Galit Fridman6 The Algorithm is Based on: l OEM - Object Exchange Model l Lorel Query Language
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Presented by: Galit Fridman7 OEM - Object Exchange Model
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Presented by: Galit Fridman8 Lorel Query Language l Uses the select..from..where clauses and additional clause with. l Provides powerful path expressions for traversing the data and rules.
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Presented by: Galit Fridman9 Standard Query l 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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Presented by: Galit Fridman10 View Specification Statements l Identify objects within a graph. l Import arbitrary subgraphs. l Add or remove objects appearing in the view.
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Presented by: Galit Fridman11 View Specification l 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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Presented by: Galit Fridman12 Materialized Views l Primary objects- objects that are bound to e. l adjunct objects - subobjects discovered by the with clause.
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Presented by: Galit Fridman13 Update Operations l Insertion and deletions of the edge. Denoted: l Change of value of the atomic object. Denoted:
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Presented by: Galit Fridman14 Incremental Maintenance Algorithm Input 1. View specification statements. 2. Update U:,, Chg,o1,Oldval,NewVal> 3. New database state DB’. 4. View instance V.
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Presented by: Galit Fridman15 Incremental Maintenance algorithm Basic Structure:
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Presented by: Galit Fridman16 Base Cost For Update Operations
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Presented by: Galit Fridman17 Database Size
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Presented by: Galit Fridman18 Number of label occurrences
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Presented by: Galit Fridman19 Length of the form clause
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Presented by: Galit Fridman20 Bound Variable Position
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Presented by: Galit Fridman21 Selectivity of the where clause
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Presented by: Galit Fridman22 Conclusion l Advantage: The algorithm outperforms recomputation of the view, even for large numbers of insert and delete edge updates. Scales well with increasing the database. l Disadvantage: can be expensive as full recomputation of the view for a single atomic value change.
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