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Object-Oriented Standards

Object-Oriented Standards. OMG OMDG. Overview. Object Management Group (OMG). International non profit-making consortium founded in 1989 to address object standards. Primary aims of OMG are: Promotion of object-oriented approach.

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Object-Oriented Standards

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  1. Object-Oriented Standards OMG OMDG

  2. Overview

  3. Object Management Group (OMG) • International non profit-making consortium founded in 1989 to address object standards. • Primary aims of OMG are: • Promotion of object-oriented approach. • Development of standards in which location, environment, language, and other characteristics of objects are transparent. • Not recognized standards group but aims to develop de facto standards.

  4. Object Management Architecture Object Model (OM) - Design-portable abstract model for communicating with OMG-compliant object-oriented systems. Object Request Broker (ORB) - Handle distribution of messages between application objects in a highly interoperable manner. Object Services - Provide main functions for realizing basic object functionality.. Common Facilities - Comprise a set of tasks that many applications must perform but are traditionally duplicated within each one.

  5. Object Model

  6. Common Object Request Broker Architecture (CORBA) • Defines architecture of ORB-based environments. • Some elements of CORBA are: • Interface Definition Language (IDL). • Type model. • Interface Repository. • Methods for getting interfaces/specifications of objects. • Provides static and dynamic mechanism for clients to issue request to objects.

  7. CORBA ORB Architecture

  8. Object Data Management Group • Established by vendors of OODBMSs to define standards. • Have produced an Object Model that specifies a standard model for the semantics of database objects. • Design of class libraries and applications using these semantics should be portable across various OODBMSs.

  9. Object Data Management Group • Major components of ODMG architecture for an OODBMS are: • Object Model (OM) • Object Definition Language (ODL) • Object Query Language (OQL) • C++, Smalltalk, and Java Language Binding.

  10. ODMG OM – Basic Modeling Primitives • Basic modeling primitives are object/literal. • Objects/literals can be categorized into types. • All objects of given type exhibit common behavior and state. A type is itself an object. • Behavior defined by set of operations that can be performed on or by object. • State defined byvalues objects carry for a set of properties.

  11. ODMG Object Model - Objects • Object types decomposed as atomic, collections, or structured types. • Objects created using new() of corresponding factory interface provided by language binding. • Each object has a unique identity, the object identifier, which does not change and is not reused when the object is deleted. • May be given one or more names by user.

  12. ODL Interface for Objects

  13. ODMG Object Model – Built-in Collections • Contains arbitrary number of unnamed homogeneous elements; each can be instance of atomic type, another collection, or a literal type. • Only collection objects have identity. • Use iterator to iterate over collection. • There are ordered and unordered collections: • ordered collections traversed first to last, or vice versa; • unordered collections have no fixed order of iteration.

  14. ODMG Object Model – Built-in Collections Set: unordered collections without duplicates. Bag: unordered collections that do allow duplicates. List: ordered collections that allow duplicates. Array: 1D array of dynamically varying length. Dictionary: unordered sequence of key-value pairs with no duplicate keys.

  15. ODMG Object Model - Relationships • Only binary relationships supported. • Traversal paths are defined for each direction of traversal. class Branch { relationship set <Staff>Has inverse Staff::WorksAt } class Staff { relationship Branch WorksAt inverse Branch::Has }

  16. Object Definition Language (ODL) module DreamHome Class Branch (extent branchOffices key branchNo) { attribute string branchNo; …. relationship Manager ManagedBy inverse Manager::Manages; void takeOnPropertyForRent(in string propertyNo) raises(propertyAlreadyForRent);}

  17. Object Query Language (OQL) • An OQL query is a function that delivers an object whose type may be inferred from operator contributing to query expression. • Query definition expressions is of form: DEFINE Q as e • Defines query with name Q given query expression e.

  18. Example 26.2 OQL: Extents & Traversal Paths (1) Get set of all staff (with identity): staff (2) Get set of all branch managers (with identity): branchOffices.ManagedBy

  19. Example 26.2 OQL: Extents & Traversal Paths (3) Find all branches in London: SELECT b.branchNo FROM b IN branchOffices WHERE b.address.city = "London“; This returns a literal of type bag<string>.

  20. Example 26.3 – OQL: Use of DEFINE Get set of all staff who work in London (without identity): DEFINE Londoners AS SELECT s FROM s IN salesStaff WHERE s.WorksAt.address.city = "London“; SELECT s.name.lName FROM s IN Londoners; This returns a literal of type set<string>.

  21. Example 26.4 OQL: Use of structures (1) Get structured set (without identity) containing name, sex, and age for all staff who live in London: SELECT struct (lName:s.name.lName, sex:s.sex, age:s.age) FROM s IN Staff WHERE s.WorksAt.address.city = "London” This returns a literal of type set<struct>.

  22. Example 26.4 OQL: Use of structures (2) Get structured set (with identity) with name, sex, and age of all deputy managers over 60: class Deputy {attribute string lName; attribute sexType sex; attribute integer age;}; Typedef bag<Deputy>Deputies; Deputies (SELECT Deputy (lName:s.name.lName, sex:s.sex, age:x.age) FROM s IN salesStaff WHERE position = "Deputy“ AND s.getAge > 60) This returns an object of type deputies.

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