The Blackboard is a common resource which is used to allow the various KS to communicate with each other. It holds the data gathered so far, and also the current set of partial solutions which are being pursued simultaneously. In order to improve control and increase data abstraction the Blackboard can be organised into a series of levels or hierarchies and KS are associated with specific levels. Often KS may read data from one level and post updated data to a higher level. This supports the ability to represent the solution, as well as the domain knowledge, in forms which best suit the various levels of solutions.
Further differentiations of the Blackboard can be achieved by incorporating several distinct panels which are used to display alternative representations of solutions, to show data read in, data inferred, levels of uncertainty and so forth.
The Control Mechanism.
In the same way that classical KBS have to oversome the problem of conflict resolution Blackboard systems also need a way of resolving situations where more than one KS indicates that it could add something to the solutions. This is done in BB through the control mechanism which co-ordinates the KS. The control mechanism looks at the current state of the BB and checks the possible things which KS indicate they can add to that state. It then decides which KS is to execute next on the basis of the current focus of attention - this shows what has just occurred on the BB and helps to inform the control mechanism of the next most appropriate type of action or object to fire. Focus of attention candidates are:
- Particular KS which can be activated next.
- Particular BB objects which should be examined next.
- A combination of KS and BB object.
Note that as the control mechanism selects a focus of attention irrespective of what it does then any form of inferencing can be performed and this is how opportunistic reasoning is an integral part of BB.
The answer is B