Group Members: Christopher Parrott, Christopher Sinclair,
David Tucker & Andrew Wan
Presentation Presenters: Christopher Parrott & Christopher Sinclair

• 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.

• About ODMG Object Model
• Database Types
 Specifications & Implementations
•
Object type definition consists of two components, they are
Interface & one or more Implementations.
U se r
Interface
U se r visible to the users of the type
not visible to the users of the type
Implementation
Class
Us er
U se r
Type Specification

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

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

• 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.
Employee Extends
Person
-Class Properties
Employee_number
Employee_dob
Employee_salary
-Class Operations
+getName()
+getDOB()
+iSalary(aAmount)
Person
-Class Properties
Person_name
Person_bloodtype
-Class Operations
+returnName()
+getBloodtype()
Work_For
Company
-Class Properties
Company_Name
Company_Address theEmployees
-Class Operations
+getName()
+printEmployees()
+employ(aEmploye e)
Type diagram of object type definition

• Attributes &
Relationships
 One To One
 One To Many
 Many To Many
Employee
WorksFor
One To One Relationship
Company theEmployees
N
One To Many Relationship
Company
Employee
Departments theManagers
N
Many To Many Relationship
N theDepartments
Manager
Examples Of Relationships
• Names
Employee
Representation of how object names can be used to represent entities with shared components jeff
Name = jeff
Dept_employ=
It_support
It_support
Employee bob
Name = bob
Dept_employ=
It_support
Department
Name = It_support
Employees = jeff, bob….

• 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.
EmployeeMetaData = William->getClass( )
• Above operation will store description of employee class.
EmployeeName = EmployeeMetaData ->getName( )
• EmployeeMetaData is used to print the employee’s name as the getName function is part of the employee class.

• Introduction
 Object’s 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
Employee
Void
+salaryIncrease(aAmount)
Company
Void
+employ(aEmployee)
Employee
Date
+dateOfBirth()
-Operation salaryIncrease defined in Employee class increases the salary property with the specified amount entered as a parameter. The operation does that return anything.
Employee theEmployees
-Operation employ defined in Company class sets a employee instance into theEmployees.
Thus adding a employee to the company. The employee instance is passed as a parameter to the operation. The operation does not return anything.
-Operation dateOfBirth returns the employee’s date of birth after calculation. The operation accepts no parameters and returns a date type.

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.

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.

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’

• 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).

• 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…’

• 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

• 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

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

• 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

 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.

Group Members: Christopher Parrott, Christopher Sinclair,
David Tucker & Andrew Wan
Presentation Presented By: Christopher Parrott & Christopher Sinclair