1. Lecture 3 From process-oriented to agent-oriented programming.
Distributed object systems.
Bond objects.
Communication.
Asynchronous communication.
Event handling.
Semantic understanding of messages. Probes.

3. Bond basics Distributed-object system.
Message passing distributed object system.
Why?
Other systems, e.g. Jini are based upon Java RMI.

4. Bond objects A Bond object extends the standard Java object with:
Unique identifier.
Communication support.
Serialization and cloning.
Dynamic properties.
Multiple inheritance.
Visual Editor.
Light-weight objects (e.g. messages, shadows)

5. Bond resident Container Object.
Directory. Each object is registered at the time of creation.
Aliases.
Communication Engine – runs at a known port on a system with a given BondIPAddress

6. Communication engine

7. Local shadow of a remote object
We wish to communicate with a remote object as if it were local. To do so we need a local representative of the remote object.
Proxy in Voyager
Stub in RMI
Stubs are used to create VONs
Shadows are used to crfeate a local copy of a remote object.

8. Communication with remote objects -bond shadows

9. Virtual Object Networks, VONs

10. Object mobility

11. Message composition
The system supports messages in KQML and XML format.
Message composition – putting all pieces together:
The contents of the message.
The source.
The destination.
The sub-protocol – we’ll talk about them later. For now think of a subprotocol as a dialect that two objects understand…..

12. KQML performatives Categories of performatives: Queries: ask;
Responses: tell;
Informational:
Generative:
Capability:
Networking:

15. Asynchronous communication using reply-waiting slots

16. Event handling
Java objects use listeners abstractions to capture events.
Corba uses an event service.
Bond uses event waiting slots.

18. The subscribe-notify model. Event waiting slots.

19. Subprotocols Dialects.
Closed sets of messages required for a “conversation”.
Each message is stamped with the subprotocol it belongs to.
Each bond object:
has a property called subprotocols implemented that lists all the subprotocols it understands.
Implements the bondAccessSubprotocol

21. Subprotocol inheritance
Static inheritance
Dynamic inheritance. Probes extend an object and allow it to speak a new protocol.
Probes are dynamic properties.