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- The blackboard structure is highly structured.
- The blackboard prescribes the organisation of domain knowledge and all
the input, intermediate and partial solutions needed to solve problems.
- The solution space is organised into one or more application-dependent
hierarchies.
- Information at each level of the hierarchy represents partial solutions.
- Domain knowledge is partitioned into individual knowledge sources.
- Transformation in the blackboard hierarchy performed using algorithmic or
heuristic procedure by interrogating knowledge modules under the control
system.
Consider a group of people assembling a jigsaw with a blackboard:
- Volunteers look at their pieces and select most promising pieces
and place then on the board.
- Each member would then look at his/her pieces and see if any fit those
already on the board. Those with such pieces evolve the solution.
- The new solutions causes other pieces to fall into place and so on.
For the solution to be a blackboard solution:
- No direct communication is allowed to take place. The jigsaw could
be assembled in total silence with no real problems.
- It would not matter who held what pieces.
- All communication is visual on the board.
- Each person is self-activating -- knowing when his/her pieces fit.
- No a priori order is established -- cooperation is mediated by state of
solution on the blackboard.
- The solution is being assembled incrementally and
opportunistically -- both important attributes of AI blackboard systems.
To illustrate the importance of the control systems consider one
constrain in the above problem:
The blackboard lies in a narrow corridor so that only one person
can view the board at a single instance.
- We now need some monitor to control how the board is viewed and the
puzzle assembled.
- This can be quite simple or could involve a lot of complex strategies,
such as viewing everybody's pieces and deciding which piece fits ``best''.
- Care will be needed so as not to compromise the one essential
characteristic of a blackboard system, opportunistic problem solving.
- Computer implementations of blackboards often face similar problems.
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dave@cs.cf.ac.uk