Implementation issues

The above example illustrates some problems that may arise when implementing a blackboard system. In this section we consider some general considerations needed when implementing and designing a blackboard framework.

Knowledge sources

• Domain knowledge should be divided up so that sources are kept separate and independent.
• Each knowledge source is responsible for knowing the conditions under which it can contribute a solution:
  • A set of preconditions are specified that must be satisfied before the source can be activated.
• Knowledge sources are represented as sets of rules, procedures or logic assertions.
• Knowledge sources only modify blackboard or control data structures. And only knowledge sources modify the blackboard (Fig 23).

Blackboard data structure

• Knowledge sources produce changes to this structure that lead incrementally to a solution.
• The data structure consists of objects from the solution space:
  • input data,
  • partial solutions,
  • alternatives,
  • final solutions,
  • control data.
• Final form of structure is problem dependent although objects are hierarchically organised tree/graph type structure.
• multiple hierarchies or blackboard panels are permitted.

Control

• Knowledge sources respond opportunistically to changes on the blackboard.
• A set of control modules monitor the changes on the blackboard and a scheduler decides what actions to take next.
• Various kinds of information are made globally available to the control modules and are stored either
  • on the blackboard, or
  • separately in control structures

  Their purpose is to focus attention.

• The focus of attention can either be:
  • blackboard structures, or
  • knowledge sources, or
  • both.
• Solutions built up on step at a time. Many kinds of reasoning (e.g. data driven, goal driven, expectation driven) have been applied.