Query processing over object views of relational data

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Query processing over object views of relational
data

• Gustav Fahl, Tore Risch
• The VLDB Journal(1997) vol 6 pp261-281

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Problem Addressed

• Mapping object views to relational database to
  handle existing relational data in a general and
  efficient way
• Direct mapping to object view, using relational
  view when relational database is not Direct
  Mappable
• Use of Domain Relational Calculus predicate to
  have relational database access by changing it to
  relational database queries
• Object Identity functions and type membership
  test enables restructuring query without
  accessing database
• Query optimization through object view with
  Object Identity and primary key mapping

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Translator

• AMOS DBMS (based on DAPLEX/IRIS) mapped type
  mapping to mapped object
• Mapped type (structure) stored in the
  translator
• Mapped object (data) stored in the RDBMS

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DM (Direct Mappable)
DM
Requires view in relational DB
DM

• Let OS be an EER/OO schema and RS the
  corresponding relational database schema. RS is
  DM to OS if
• For each type TP in OS there exists a relation
  R in RS such that there is a one-to-one mapping
  between instances of TP and tuples in R

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Object Identity generation

• Algorithmic generation - Pegasus project
• Mathematical correspondence with primary key
• Can add type information
• OID mapping table - AMOS
• Allows query generation without accessing the
  external (relational) database where the data
  stored
• Existence of OID in translator cannot guarantee
  existence of primary key in the external database
• Check validity during the query process

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Object Identity

• oid map function
• Takes object return primary key
• Requires query to relational database
• Object is object itself
• oid translate function
• Resides in translator
• Object is OID

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Type membership test

• Check objects type without accessing the
  relational database (i.e. early binding)
• ex) query for type salesman required before
  subsequent (2nd) query(the required result)
• select salary(s) for each salesman s
• -gt select salary from employee where enr
• (select enr from salesman)
• -gt 1st. X select enr from salesman
• 2nd. select salary from employee where enr
  X
• Use oid translate function

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Query optimization
oid translate function
S does not occur in any other predicate and is
not result variable
select salary from employee, salesman where
employee.enr salesman.enr
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Summary

• Purpose Making SQL query from OQL(AMOSQL)
• Each (object oriented) class is represented by
  exactly one (relational) table
• OID, OID mapping and OID function is the main
  idea
• Late binding issues
• DM relational view for ill defined relational
  database

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Question

• In OID and primary key mapping, what is the
  disadvantage of using mapping table rather than
  algorithm?
• What kind of relational table is unable to have
  Direct Mappable relational view with current
  relational view definition language?
• Why does late binding cause expensive query for
  this system?
• What is the difference between oid map function
  and oid translate function?
• What kind of strategy can be used to check
  oid/primary key mapping when deletion and add of
  data happened in relational database?