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Implementing and Using Blackboards

• Blackboards + linda stile interaction: basic but very useful means of communication and synchronization.
• Present in many systems: SICStus, BinProlog/-Prolog, &-Prolog/CIAO, ...
• Basic features:
  • out/1: write tuple
  • rd/1: read tuple
  • in/1: remove tuple
  • rd_noblock/1 and in_noblock/1
  • in/2 and rd/2 (on disjunctions)
• Possibly, have several (possibly hierarchical) blackboards - then, extra argument to primitives specifies which blackboard. Also, specification of location of blackboard, creation of clients, etc.
• Implementation approaches:
  • Blackboard is a Prolog process. Tuples maintained via assert/retract. Communication, e.g., via sockets (allows Internet-wide use of the blackboard).
  • Support blackboard internally in system (possibly, in conjunction with asserted database).
  • Mixed approach: local vs. remote blackboards.
  • Clients can be created using standard process creation primitives (e.g., ``sh'' and ``rsh''), or dedicated port servers.