Seminarium on Component-based Software Engineering

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Seminarium onComponent-based Software
Engineering
CORBA

• Jan Willem Klinkenberg

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Object Management Group (OMG)

• Consortium of Computing Industry
• Founded in 1989
• Non profit
• around 800 members
• Goal standardization of whatever it takes to
  achieve interoperability on all levels of an open
  market for objects

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OMG

• Original effort fix wiring problem
• How can distributed object-oriented systems
  implemented in different languages and running on
  different platforms interact?
• Incompatibility between compilers
• Differences in object models
• Differences in platforms
• Solution CORBA

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CORBA

• Common Object Request Broker Architecture.
• Open standard
• 1991 version 1.0
• Initial version.
• 1995 version 2.0
• IIOP
• OMA
• More languages support
• 2002 version 3.0
• Corba Component Model (CCM)
• Scripting languages support

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CORBA

• CORBA - Common Object Request Broker Architecture.

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IDL

• Interface Definition Language
• Defines all object interfaces in a common
  language
• Bindings are available for C, C, Java, Python,
  Smalltalk, Cobol, etc
• An IDL compiler generates stubs and skeletons.
• Stubs
• Looks like local object
• Marhals arguments
• Forwards all invocations through ORB to target
  object
• Skeletons
• Receives invocations from ORB
• Unmarshals arguments
• Invokes target methods
• Sends back return value

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IDL example

• module Example
• struct Date
• unsigned short Day
• unsigned short Month
• unsigned short Year
• interface Ufo
• readonly attribute unsigned long ID
• readonly attribute string Name
• readonly attribute Date FirstContact
• unsigned long Contacts()
• void RegisterContact(out Date dateOfContact)

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IDL types

• IDL distinguishes between basic and constructed
  type and CORBA object references.
• Before CORBA 2.3, only references
• Since CORBA 2.3, call by value is supported -gt
  standard mapping by XML

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DII and DSI

• Sometimes binding can be too static
• DII Dynamic invocation interface
• DSI Dynamic skeleton interface (since Corba 2.0)
• These interfaces allow for dynamic selection of
  methods at client side or server side

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ORB

• Object Request Broker
• Routes the method invocations
• Interface repository
• Implementation repository
• Can load and start object servants
• Can communicate with other ORBs using IIOP

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CORBA and OMG IDL
IDL source
Applications Programs
IDL compiler
Object servants
Dynamic invocation interface
IDL stubs
ORB interface
Object Adapter
IDL Skeletons
Dynamic Skeleton interface
Object Request Broker (ORB)
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Object Adapter

• Object servants register with ORB via the object
  adapter.
• Servants are loaded and started by ORB via
  adapter.
• BOA Basic Object Adapter
• Under specified, deprecated in 1998
• POA Portable Object Adapter
• Replaced the BOA
• Essential for several CCM features
• Creates object references
• Several possible policies for object creation

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Server, client or both

• Separation of client and called object does not
  impose an asymetric architecture.
• The same process can issue and receive calls.
• Pure application programs do not require
  registration with ORB

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CORBA v.1 - Problems

• An ORB is essentially an remote incovation
  service
• Replaces sockets and remote procedure calls in
  distributed applications with a cleaner model
• So whats the problem?
• Applictions still have to share many conventions
  to interoperate
• OMG had to broaden its focus.

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OMA - Object Management Architecure

• Since CORBA 2.0
• Adds new areas of standardization
• CORBAservices
• Common object services e.g. naming, trader
  event, security
• CORBAfacilities defines a specific component
  framework than can be used to integrate
  components.
• Horizontal domain independent, focus on specific
  application models e.g. printing facilities
• Vertical domain specific e.g. healtcare, finance
• Application object specifications (currently
  void)
• CCM - CORBA Component Model (since 3.0)

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CORBA Services supporting enterprise distributed
computing

• Naming service
• White pages
• Trader service
• Yellow pages
• Event service
• Send event objects from event suppliers to event
  consumers.
• Notification service
• Add QoS, filtering, etc. to Event service
• Object transaction service
• Security Service
• Encryption, authentication

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CORBA Services supporting architecture using
fine-grained objects

• Concurrency control service
• Lock and release resources
• Licensing service
• For non-freeware objects
• Lifecycle service
• Creation, copying, moving and deletion of objects
• Relationship service
• Not used or implemented
• Persistant state service
• Allows storing and retrieving of objects

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CORBA Services continued

• Externalization service
• Mapping of object into stream and back
• Properties service
• Add/delete and retrieve arbitrary properties to
  objects
• Object query service (not implemented)
• Locate object instance by attributes
• Object collections service (not implemented)
• Provides collection types like sets, trees,
  queues or lists.
• Time service
• Provides a universal time for the distributed
  system

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CCM - Corba Component Model

• Introduced with CORBA 3.0 in 2002
• Logical extension of Enterprise JavaBeans
• Is an architecture for defining components and
  their interactions
• Provides a packaging technology
• Provides a container implementation framework
  (CIF)

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CCM Component
Component interface
My Business Component
Facets
Receptacles
OFFERED
REQUIRED
Event sinks
Event sources
Attributes
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CCM Components features

• Ports
• Facet provided interface
• Receptacle required interface
• Event sources
• Event sinks
• Primary keys
• Instance identification for client
• Attributes
• Home interfaces
• Provides factory functionality

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CCM packaging
CCM Assembly
CCM Component
CCM Component
Segments
Deployment configuration
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CCM Containers

• Component instances are placed inside containers

Home interface
Home for C
Component C
Callbacks
Services
Container
Components interact with POA as well as
transaction, security, persistence and
notification services via interfaces on their
container
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Components types

• There are different types of components
• Service
• Session
• Entity
• Process

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CIF

• Component Implementation Framework
• Described in CIDL, Component implementation
  Definition Language
• Creates programming skeletons that automate many
  of the basic behaviors of components, including
  navigation, identity inquiries, activation, state
  management, lifecycle management, and so on.

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Questions?

• ?