Transcript Common Object Request Broker Architecture (CORBA)

Common Object Request
Broker Architecture
(CORBA)
By:
Sunil Gopinath
David Watkins
Introduction
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What is the purpose / goals of CORBA?
How to meet goals?
Example
Conclusion
What is the purpose / goals of CORBA?
• Enable the building of plug and play
component software environment
• Enable the development of portable, object
oriented, interoperable code that is
hardware, operating system, network, and
programming language independent
How to meet goals?
• Interface Definition Language (IDL)
• Object Request Broker (ORB)
Interface Definition Language (IDL)
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Language Independence
Defines Object Interfaces
Hides underlying object implementation
Language mappings exist for C, C++, Java,
Cobol, Smalltalk, and Ada
Interface Definition Language (IDL)
module <identifier>
{
interface <identifier> [:inheritance]
{
<type declarations>;
<constant declarations>;
<exception declarations>;
<attribute declarations>;
[<op_type>] <identifier>(<parameters>)
[raises exception][context];
}
}
Defines a container
(namespace)
Defines a
CORBA object
Defines a
method
IDL Compiler
IDL
Definitions
1.
2.
IDL
Compiler
Stubs
3.
Define objects using
IDL
Run IDL file through
IDL compiler
Compiler uses language
mappings to generate
programming language
specific stubs and
skeletons
Skeletons
Object Request Broker (ORB)
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What is it?
Architecture
Request Handling
Scenario
CORBA Services
CORBA Facilities
What is it?
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Implementation of CORBA specification
Middleware product
Conceptual Software Bus
Hides location and
Application
implementation details
Middleware
about objects
OS
Hardware
Drivers
Client / Object Interaction
Client
Obj Impl
Client
Obj Impl
IDL
IDL
IDL
IDL
Network
IPX
ATM
OSI
TCP/IP
IPX
ATM
ORB
OSI
TCP/IP
ORB
ORB Architecture
Interface
Repository
Client
IDL
Stub
IDL
Compiler
Implementation
Repository
Object (servant)
OBJ
Ref
DII
GIOP/IOOP
ORB
Interface
IDL
Skeleton
ORB Core
DSI
Object Adapter
Interface Repository
Interface
Repository
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Database of object definitions
Contains metadata about each object
Allows for introspection
Allows clients to discover interfaces at run-time
Used in support of dynamic invocations
Object Adapter
IDL Compiler
IDL
Compiler
• Compiles IDL definition into stubs and
skeletons
• Uses OMG specified language mappings
to translate IDL into a language specific
implementation
Object Adapter
Implementation Repository
Implementation
Repository
• Contains information that allows the ORB
to locate and activate object
implementations
• Provides information about the classes a
server supports, the objects that are
instantiated, and their IDs
Object Adapter
ORB Core
• Provides mechanism for transparently
communicating client requests to target
object implementations
• Makes client requests appear to be local
procedure calls
• GIOP – General Inter-ORB Protocol
• IIOP – Internet Inter-ORB Protocol
Object Adapter
GIOP/IOOP
ORB Core
ORB Interface
Client
Object (servant)
ORB
Interface
• Provides helper functions
• Converting object
references to strings
Object Adapter
• Creating
argument
lists for requests made
through DII
IDL Stub
Client
IDL
Stub
• Static invocation
interface (SII)
• Marshals application
data into a common
packet-level
representation
– Network byte order
(little-endian or bigendian)
– Size of data types
IDL Skeleton
• Demarshals the
packet-level
representation back
into typed data that is
meaningful to an
application
– Network byte order
(little-endian or bigendian)
– Size of data types
Object (servant)
IDL
Skeleton
Dynamic Invocation Interface
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Client
Dynamically issue requests to objects
without requiring IDL stubs to be
linked in
Clients discover interfaces at runtime and learn how to call them
Steps:
DII
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Obtain interface name
Obtain method description (from
interface repository)
Object
Create argument
list Adapter
Create request
Invoke request
Dynamic Skeleton Interface
• Server side analogue to DII
• Allows an ORB to deliver
requests to an object
implementation that does
not have compile-time
knowledge of the type of
object it is implementing
Object (servant)
DSI
Object Adapter
Object Adapter
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Accept requests for service on behalf
of the server’s objects
Demultiplexes requests to the correct
servant
Dispatches the appropriate operation
upcall on the servant
Registers classes it supports and their
run-time instances with the
implementation repository
Portable Object Adapter (POA)
• policies control object behavior
(ie. LifespanPolicy)
Instance of the adapter design pattern
Object (servant)
IDL
Skeleton
DSI
Object Adapter
Object Reference
Client
OBJ
Ref
Object (servant)
• Interoperable Object Reference (IOR)
• Uniquely identifies each object
• Contents
• Type Name (repository ID) Object Adapter
• Protocol and Address Details
• Object Key (object adaptor name, object name)
Request Handling
Server Application
POA
Incoming
Request
ORB
POA
POA
Servants
Scenario
Interface
Repository
Client
IDL
Stub
IDL
Compiler
Implementation
Repository
Object (servant)
OBJ
Ref
DII
GIOP/IOOP
ORB
Interface
IDL
Skeleton
ORB Core
DSI
Object Adapter
CORBA Services
• Provide basic infrastructure functionality
• Currently there are 15 defined services
– Naming - maps human names to object references
(White Pages)
– Event - provides both a push and pull event model
– Object Trader - discover objects based on the services
they provide (Yellow Pages)
– Transactions – allows distributed objects to participate
in atomic transactions
CORBA Facilities
• Provide higher-level functionality at the
application level
• Provide standard components that can be used
“off-the-shelf”
• Two Categories
– Horizontal – user interface, information management,
systems management, and task management
– Vertical – domain based, telecommunications, financial
services
Example
Conclusion
• Distributed object, component architecture
• Real world examples of design patterns
– TAO – freeware ORB
• Adapter, Factory, Reactor, Strategy
• Plugable Transports
• CORBA Beans
References
• www.omg.org
• www.cs.wustl.edu/~schmidt/corba.html
• http://www.infosys.tuwien.ac.at/Research/Corba/
OMG/arch2.htm
• Communications of the ACM, October 1998
• Jeri Edwards, Dan Harkey, and Robert Orfali.
Instant CORBA. New York: Wiley Computer
Publishing, 1997.