5. Discussions and Conclusion

The PVM is a system for distributed processing implementations that offers tools for communication between tasks, like point to point messages and broadcasts, and tools to control the spawning of tasks. It was chosen due to the simplicity it allows in the implementation of message exchanges between the agents, and because it allows the definition of which workstation a process must run. Besides that, it is widely used in the academic community, which means better support for developers, having available an Internet newsgroup where assistance can be found. Finally, we present an example that shows, in a LISP like manner, the messages that are exchanged when an object moves in the workspace during an assembly. First, the Collision-Avoider agent requests the control of the manipulator to avoid the possible collisions; the Assembler agent agrees with the requisition and transfers the control to the Collision-Avoider; when the danger of a possible collision ceases, Collision-Avoider releases the control of the resource, which is requested by Assembler; the request is accepted by Collision-Avoider and Assembler gets the control and returns to its job. comment: the control is with the Assembler.