PART V

1
PART V the ORB

• or
• The thing which does the job.

2
The Common Object Request Broker Architecture
3
The ORB A Pseudo Object

• CORBA is primarily a specification for accessing
  remote objects.
• However, we can as well use the IDL for the
  specification of local objects.
• These objects (as e.g. the ORB) are called pseudo
  objects.

4
Pseudo IDL

• Pseudo objects use Pseudo IDL (also called PIDL)
  to describe their interfaces.
• The PIDL is essentially identical to the IDL,
  except the intention is that the object of a PIDL
  interface is not associated with an Object
  Reference for the purposes of remote access.
• In reality, things are more difficult, e.g. a
  PIDL does not need to compile...

5
Example

• The pseudo IDL definition of the
  object_to_string() operation
• interface ORB // PIDL
• // ...
• string object_to_string ( in Object obj )
• Object string_to_object (in string str )
• // ...

6
Example

• The pseudo IDL definition of the
  object_to_string() operation
• interface ORB // PIDL
• // ...
• string object_to_string ( in Object obj )
• Object string_to_object (in string str )
• // ...

Object is also defined in pseudo IDL somewhere
else.
7
The ORB Interface

• The ORB provides the following tasks
• Initialisation.
• (already seen in the example)
• Converting object references into strings and
  vice versa.
• (already seen in the example)
• Obtaining a reference to a POA
• (see next slide)

8
The POA

• The Portable Object Adapter (POA) allows dynamic,
  scalable handling of object references on the
  server side.
• It is a more sophisticated and flexible version
  than the simple connect() method seen in the
  example.
• POA systems allow different lifetimes for the
  object reference and the servant.

9
POA ExampleSanta Claus as a CORBA Object

• The client side
• The client (usually a young child) sends a
  request to Santa Claus asking for special gifts
  under the Christmas tree.
• The client goes to bed.
• The client finds the requested presents under the
  tree (if it is 25th of December).

10
POA ExampleSanta Claus as a CORBA Object

• The server side
• The server (usually the parents) buys the
  requested presents (or not).
• The presents are wrapped.
• The wrapped presents are strategically located
  under the Christmas tree.

11
POA ExampleSanta Claus as a CORBA Object

• What we learn
• Client and server may have different viewpoints
  of the object implementation.
• Client and server may have different points of
  view of the the objects lifetime.
• Dynamic object implementation allows serving
  millions of clients (children) by one single
  object (Santa Claus), therefore featuring
  scalability.

12
Summary

• The ORB is defined by the PIDL.
• The PIDL is an IDL for local objects.
• Santa Claus does exist.
• But Santa Claus implementation is different from
  how he is perceived by the children (the
  clients).
• Similarly, the POA facilitates a flexible and
  scalable implementation of objects behaviour.