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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.

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The ODMG Standard 2.0 Focusing On The ODMG Object Model

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  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

  2. 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.

  3. 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

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

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

  6. 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. Modelling State Type diagram of object type definition

  7. 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

  8. 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 employee’s name as the getName function is part of the employee class. Modelling State EmployeeMetaData = William->getClass( ) EmployeeName = EmployeeMetaData ->getName( )

  9. 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 Modelling Behaviour

  10. 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.

  11. 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.

  12. 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’

  13. 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).

  14. 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…’

  15. 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

  16. 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

  17. The New ODMG 3.0 Standard • What's new in the ODMG 3.0 Standard • Object Model

  18. 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

  19. 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.

  20. End Of Presentation The ODMG Standard 2.0Focusing On The ODMG Object Model Group Members: Christopher Parrott, Christopher Sinclair, David Tucker & Andrew Wan Presentation Presented By: Christopher Parrott & Christopher Sinclair • Any Questions?

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