The ODMG Standard 2.0 Focusing On The ODMG Object Model

1
The ODMG Standard 2.0Focusing On The ODMG Object
Model

• Group Members Christopher Parrott, Christopher
  Sinclair, David Tucker Andrew Wan

Presentation Presenters Christopher Parrott
Christopher Sinclair
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Introduction

• ODMG (Object Data Management Group) formed in
  1991.
• Independent organisation to standardise Object
  Oriented Database Management Systems.
• Corporate members includes Sun, Poet Computer
  Associates.
• ODMG covers following key areas
• Object Model (OM)
• Object Definition Language (ODL)
• Object Query Language (OQL)
• C, Java Smalltalk Bindings.

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The Object Model

• About ODMG Object Model
• Database Types
• Specifications Implementations
• Object type definition consists of two
  components, they are Interface one or more
  Implementations.

Type Specification
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Objects

• Object Identifiers
• Object Lifetime
• Collections
• Collection Objects
• Set Objects
• Bag Objects
• List Objects
• Array Objects
• Dictionary Objects

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Objects

• Literal Values.
• ODMG model supports several literal types
• Atomic
• Collection
• Structured
• Object Hierarchy

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Modelling State

• Introduction
• Provides description of data structure relates
  interfaces to a set of object types in a type
  hierarchy.
• Object Type Interfaces
• Describes how data can be stored relations to
  other types of data.

Type diagram of object type definition
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Modelling State

• Attributes Relationships
• One To One
• One To Many
• Many To Many
• Names

Examples Of Relationships
Representation of how object names can be used
to represent entities with shared components
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Modelling State

• Metadata
• Descriptive information about persistent objects
  that defines the schema.
• Used by ODBMS to define structure .
• Metadata is stored in an ODL Schema Repository.
• Considered important for object oriented database
  systems.
• Example of a operation that returns the class of
  an object.
• Above operation will store description of
  employee class.
• EmployeeMetaData is used to print the employees
  name as the getName function is part of the
  employee class.

EmployeeMetaData William-gtgetClass( )
EmployeeName EmployeeMetaData -gtgetName( )
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Modelling Behaviour

• Introduction
• Objects behaviour is defined by its set of
  operations.
• Operation has its specific type defined.
• Operations
• Described as a piece of code fragment.
• Manipulates the properties and data of object.
• Exceptions

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Concurrency Transaction Control

• ODMG view on locking Concurrency Control
• Locking Control
• Types of locks
• Read Locks
• Write Locks
• Upgrade Locks
• Prevention against form of deadlock when two
  processes both obtain read locks on object then
  attempt to obtain a write lock on the same
  object.
• Deadlock avoided initially by obtaining upgrade
  lock instead of read locks for all objects user
  intends to modify.
• Avoids potential conflicts when write lock is
  later obtained.

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Concurrency Transaction Control

• Lock Duration
• Concurrency Control
• Transactions
• All programs that implements persistent objects
  must be organised into transactions.
• Once transaction commits, ODBMS guarantees
  changes made by transaction are never lost.
• ODMG data supports traditional ACID (Atomicity,
  Consistency, Integrity Durability).
• Transactions are started with begin command,
  similar to new command when creating objects.
• Transactions can be initiated started
  explicitly.

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Concurrency Transaction Control

• Event Management
• Managing Logical Databases
• ODBMS can manage one or more logical databases.
  All of these logical databases are instances of
  type database.
• Instances of type database created using
  DatabaseFactory interface.
• Query identifies part of data explicitly by
  naming or by specifying conditions.
• Database type also supports operations designed
  to aid the administration of the whole system.
  Such operations include
• Delete
• Move
• Copy
• Backup
• Restore all of which to keep database in Good
  Order

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Object Specification Languages

• About Object Specification Languages
• Used in representation of ODMG compliant object
  database management systems.
• Composed of independent languages used in the
  definition of schemas.
• Objectives of these independent languages are
• Provide portability of databases across ODMG
  compliant implementations.
• Interoperability of OODMS from different
  multiple vendors.
• One of main OSL languages is ODL (Object
  Definition Language), there is also OIF (Object
  Interchange Format).

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Object Query Language

• About Object Query Languages
• Developed by ODMG for use with ODMG databases.
• Language Provides mechanism by which user can
  request a subset of data from a database, such
  requests referred to as ad hoc.
• Object Query Language (OQL) is part of the SQL
  family of languages.
• Contains query syntax from SQL such as
• Select From Where

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Bindings

• The idea of Bindings
• Binding creates association between run-time
  system of programming language the persistent
  store of database system.
• Usually takes the form of library functions which
  access the DBMS functionality.
• ODMG standard implements bindings based on one
  fundamental principle
• The programmer should perceive the binding as a
  single language for expressing both database
  programming operations, not two separate
  languages with arbitrary boundaries between
  them. ODMG 2.0, 1997

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Literature Review

• Alagic, Suad
• 1996/1997
• The ODMG Object Model Does it Make Sense?
• OOPSLA (ACM Conference on Object-Oriented
  Programming, Systems, Languages, and
  Applications) USA
• Chaudhri, Akmal B.
• 1997
• Experiences Using Object Data Management In the
  Real World
• OOPSLA 1997 Workshop

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The New ODMG 3.0 Standard

• What's new in the ODMG 3.0 Standard
• Object Model

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Conclusions

• The ODMG standard Its Real World Application.
• Conclusions Criticisms of the ODMG Object
  Model.
• ODMG model requires careful examination before it
  is accepted.
• Not yet industry standard.
• Type checking system in ODMG model is not
  perfect.
• Dynamic type checking used, but will always be in
  situations where it fails.
• Means that run-time checks will have to be used.
• Reduces Efficiency Reliability of overall
  system.
• Parametric types not supported in current issue
  of the object model.
• Except in C Bindings

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Conclusions

• Lack of self type.
• Complaints towards ODMG model relate to the fact
  that it is not a formal, mathematical model.
• ODGM model does have problems, but the model
  itself is still work in progress.
• Most likely to be adjusted to solve some of the
  major weaknesses in current version.

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The ODMG Standard 2.0Focusing On The ODMG Object
Model
End Of Presentation

• Group Members Christopher Parrott, Christopher
  Sinclair, David Tucker Andrew Wan

Presentation Presented By Christopher Parrott
Christopher Sinclair

• Any Questions?