1 PART V the ORB or The thing

1 PART V – the ORB or: The thing which does the job. 25/12/2021 Marc Conrad - University of Luton 1

2 The Common Object Request Broker Architecture 25/12/2021 Marc Conrad - University of Luton 2

3 The ORB – A Pseudo Object n n n 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. 25/12/2021 Marc Conrad - University of Luton 3

4 Pseudo IDL n n 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. n 25/12/2021 In reality, things are more difficult, e. g. a PIDL does not need to compile. . . Marc Conrad - University of Luton 4

5 Example n The pseudo IDL definition of the object_to_string() operation: n n n 25/12/2021 interface ORB { // PIDL //. . . string object_to_string ( in Object obj ); Object string_to_object (in string str ); //. . . }; Marc Conrad - University of Luton 5

6 Example n The pseudo IDL definition of the object_to_string() operation: n n n 25/12/2021 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. Marc Conrad - University of Luton 6

7 The ORB Interface The ORB provides the following tasks: n Initialisation. n n Converting object references into strings and vice versa. n n (already seen in the example) Obtaining a reference to a POA n 25/12/2021 (see next slide) Marc Conrad - University of Luton 7

8 The POA n n n 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. 25/12/2021 Marc Conrad - University of Luton 8

9 POA Example Santa Claus as a CORBA Object n The client side: n n n 25/12/2021 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 25 th of December). Marc Conrad - University of Luton 9

10 POA Example Santa Claus as a CORBA Object n The server side: n n n 25/12/2021 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. Marc Conrad - University of Luton 10

11 n POA Example Santa Claus as a CORBA Object What we learn: n n n Client and server may have different viewpoints of the object implementation. Client and server may have different points of view of the objects lifetime. Dynamic object implementation allows serving millions of clients (children) by one single object (Santa Claus), therefore featuring scalability. 25/12/2021 Marc Conrad - University of Luton 11

12 Summary n n n 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. 25/12/2021 Marc Conrad - University of Luton 12