Object-Oriented Standards

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Object-Oriented Standards

• OMG
• OMDG

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Overview
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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.

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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.

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Object Model
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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.

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CORBA ORB Architecture
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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.

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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.

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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.

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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.

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ODL Interface for Objects
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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.

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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.

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ODMG Object Model - Relationships

• Only binary relationships supported.
• Traversal paths are defined for each direction of
  traversal.
• class Branch
• relationship set ltStaffgtHas inverse
  StaffWorksAt
• class Staff
• relationship Branch WorksAt inverse BranchHas
  

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Object Definition Language (ODL)

• module DreamHome
• Class Branch
• (extent branchOffices key branchNo)
• attribute string branchNo
• .
• relationship Manager ManagedBy inverse
  ManagerManages
• void takeOnPropertyForRent(in string propertyNo)
• raises(propertyAlreadyForRent)

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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.

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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

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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 bagltstringgt.

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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 setltstringgt.

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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 (lNames.name.lName, sexs.sex,
• ages.age)
• FROM s IN Staff
• WHERE s.WorksAt.address.city "London
• This returns a literal of type setltstructgt.

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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 bagltDeputygtDeputies
• Deputies (SELECT Deputy (lNames.name.lName,
• sexs.sex, agex.age)
• FROM s IN salesStaff
• WHERE position "Deputy AND s.getAge gt 60)
• This returns an object of type deputies.