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OBJECT ORIENTED QUERY LANGUAGES. Object Oriented Database Seminar Omar Alasam Julien Aubry Julien Fontaine Bénédicte Gruss School of Computing Beng CNDS 4 Napier University. PLAN. Background Requirements Specifications Divergence from SQL Current Situation Query optimisation

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object oriented query languages

OBJECT ORIENTED QUERY LANGUAGES

Object Oriented Database Seminar

Omar Alasam

Julien Aubry

Julien Fontaine

Bénédicte Gruss

School of Computing

Beng CNDS 4 Napier University

slide2
PLAN
  • Background
  • Requirements
  • Specifications
  • Divergence from SQL
  • Current Situation
  • Query optimisation
  • Future Direction
background
Object-Oriented Databases Concepts

Objects and Identity

Complex objects

Encapsulation

Classes

Inheritance

Overloading, Overriding and late binding

BACKGROUND
background 2
BACKGROUND 2

Query Languages

  • SQL took 15 years to become the standard of RDBMS
  • Programming languages were first used to query OODB
  • Users demand on a SQL-like query facility for OODB.
  • No standard yet accepted
  • Today, each OODBMS has its own query language implemented.
ooql requirements
OOQL Requirements
  • The Object-Oriented Database System Manifesto, 1989
    • High level language
    • Efficient
    • Application independent
  • Used to interactively query the database on-line.
oql requirements
OQL requirements
  • An OQL should provide:
    • Descriptiveness
    • Closure
    • Completeness
    • Expressive power
    • Extensibility
    • orthogonality
query language issues
Query Language issues
  • Should the query language be integreted in the programming language?
  • How to access the data:
    • Simple data
    • Complex data
  • What is a result to a query ?
query language issues 2
Query language issues 2
  • Possibility to make join request
  • Management of sets of objects
  • Equal access to attributes and methods
  • Consequences of class hierarchy
sql versus oql
SQL versus OQL
  • New concepts have to be added to SQL:
    • Object IDs
    • Members
    • Methods
    • Derived data
    • Hierarchy
    • Recursion
o2 query
O2 Query
  • Query language used by O2 DBMS
  • 2 Modes:interactive & programming
  • When interactive, can violate encapsulation
  • High-level SQL-like language
  • Generic methods already defined
lifoo
LIFOO
  • Used by O2
  • Pure interrogation language
    • Quantification, aggregation and Ordering OK
    • Does not support recursive queries
  • Functional language (handles functional syntax ; min, max..)
gemstone
Gemstone
  • Result of a query: set of class identical as the queried class
  • Queries: Boolean operations combined to path expression:

Tasks select: {:t | (t.man_years > 20 & (t.leader.specialization = ‘DB’)}

slide13
OSQL
  • Used by IRIS
  • Very close to SQL
    • Syntax
    • Use of recursive cursor
  • Result of a query is an existing object
  • Aggregation and Ordering not supported
    • Foreign functions can be used
    • Data Model is Multi-Model
sql 3
SQL 3
  • Object-Oriented version of the famous QL
  • Use of ADT so as to describe classes
  • Encapsulation assured thanks to flags
  • Use of constructors, destructors and actors
  • Compatibility with SQL 92

ADT:Abstract Data Type

slide15
OQL
  • Defined by ODMG
  • OQL adopts the type system of the application
  • Functional Query Language
  • Orthogonal Query Language
query optimisation
Query Optimisation
  • Introduction: Difficulties of OODBMS Queries.
  • Optimisation Issues
    • Additional Data Types: definition of new types and classes through inheritance can both assist and prevent optimisation of queries
    • Complex Objects: The path expressions and query closure of OODBMS query languages complicate the processing of queries in several ways
    •  Methods and Encapsulation: creation of new objects, object identities (OIDs).
    • Cost Determination of evaluating methods.
optimisation issues cont
Optimisation Issues Cont.
  • Algebras and Calculi Optimisation:
    • The lack of a standard,
    • Algebra is variable based.
    • Algebraic optimisation has the advantage that a query can be transformed using well-defined operators.
  • Extensible Optimisers:
    • Ability to change with time through ``Optimiser Generators'': builds optimisers based on information on the data model, query language, algebra, calculi and cost model. 
scope of future work
Scope of Future Work
  • A Standard Extensible Optimiser Framework.
  • Better Cost Models.
  • Better Algebras and Rewrite Systems.
  • Eliminating Method Evaluation.
  • Indexing of Path Expressions.
  • Pre-computation and Caching.
solutions and evaluation
Solutions and Evaluation:
  • Simple evaluation, dynamic programming methods, Evolutionary Algorithms and randomised search.
  • Final words on Query Optimisation:
    • It is hard to provide a scheme for evaluating the success of a research into query optimisation, the only real criterion being faster average execution time of queries.
ooql future directions
OOQL Future Directions
  • Innovation in the area of OODBMS query languages !
  •  Research in OOQL:
    • Super OODBMS Query Language:
    • Polishing ODMG-93 OQL
    • Connection to Rule Systems
    • End-users Queries
    • Graphical Query Construction
ooql future directions 2
OOQL Future Directions 2
  • Future Work Scope and Expectations from:
    • ODMG-93 OQL and Rule Systems.
    • Implementation before evaluation.
    • Good end-user OODBMS query mechanism driven by strong industrial backing.
conclusion
Conclusion
  • ODMG defined a standard with OQL
  • OQL is competing with SQL 3
  • Vendors also have their own OOQL
  • The popularity of OODB depends a lot on the query language that will be adopted.