Transcript The ODMG Standard 2.0 Focusing On The ODMG Object Model

The ODMG Standard 2.0
Focusing On The ODMG Object Model
Group Members: Christopher Parrott, Christopher Sinclair,
David Tucker & Andrew Wan
Presentation Presenters: Christopher Parrott & Christopher Sinclair
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:
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Object Model (OM)
Object Definition Language (ODL)
Object Query Language (OQL)
C++, Java & Smalltalk Bindings.
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.
U
se
r
Interface
Us
er
visible to the users of the type
not visible to the users of the type
Implementation
Class
Us
Us
er
Type Specification
er
Objects
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Object Identifiers
Object Lifetime
Collections
Collection Objects
Set Objects
Bag Objects
List Objects
Array Objects
Dictionary Objects
Objects
• Literal Values.
 ODMG model supports several literal types:
• Atomic
• Collection
• Structured
• Object Hierarchy
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.
Person
-Class Properties
Person_name
Person_bloodtype
-Class Operations
Employee Extends
Person
+returnName()
+getBloodtype()
Company
-Class Properties
-Class Properties
Employee_number
Employee_dob
Employee_salary
Company_Name
Company_Address
theEmployees
-Class Operations
+getName()
+getDOB()
+iSalary(aAmount)
-Class Operations
Work_For
+getName()
+printEmployees()
+employ(aEmploye
e)
Type diagram of object type definition
Modelling State
• Attributes &
Relationships
 One To One
 One To Many
 Many To Many
Employee
Company
WorksFor
One To One Relationship
Company
Employee
theEmployees
N
One To Many Relationship
Departments
Manager
N
theManagers
theDepartments
N
Many To Many Relationship
Examples Of Relationships
• Names
Employee
Employee
jeff
Representation of how object
names can be used
to represent entities
with shared components
bob
Name = jeff
Dept_employ=
It_support
Name = bob
Dept_employ=
It_support
Department
It_support
Name = It_support
Employees = jeff, bob….
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.
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.
Modelling Behaviour
• 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)
-Operation salaryIncrease defined in Employee
class increases the salary property with the
specified amount entered as a parameter. The
operation does that return anything.
Company
Void
+employ(aEmployee)
Employee
Date
+dateOfBirth()
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:
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Delete
Move
Copy
Backup
Restore all of which to keep database in ‘Good Order’
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).
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…’
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
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
The New ODMG 3.0 Standard
• What's new in the ODMG 3.0 Standard
• Object Model
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
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.
End Of Presentation
The ODMG Standard 2.0
Focusing On The ODMG Object Model
Group Members: Christopher Parrott, Christopher Sinclair,
David Tucker & Andrew Wan
Presentation Presented By: Christopher Parrott & Christopher Sinclair
• Any Questions?