Blackboard architecture is an approach to problem solving that involves multiple knowledge sources working together on a blackboard to solve complex problems. Each knowledge source watches the blackboard for opportunities to contribute to the solution. Contributions are added to the blackboard for other knowledge sources to use. This process continues until the problem is solved. The blackboard architecture was first used in the HEARSAY-II speech understanding system, which used different knowledge sources like signal processing and semantic analysis to coordinate the complex task of speech understanding by sharing information on a blackboard.

1. Blackboard Architecture
• It is used for problem solving especially for a complex problem
which a single expert is not able to handle. Example: multilingual
translation.
• In general, problem-solving in blackboard architecture begins with
the announcement of a problem and writing initial data onto the
blackboard.
• The specialists are watching the blackboard looking for an
opportunity in order to make a contribution to solution
development.
• When a specialist finds this opportunity, they record the
contribution on the blackboard, in the hope that others will use his
contribution for final problem-solving. This process continues until
the problem is solved.

2. Components of Blackboard architecture:
• Knowledge sources: Knowledge sources (KSs) are "independent
modules that contain the knowledge needed for problem-solving" .
KSs need to focus on the progress of solving the current problem
However, it is not necessary for a KS to communicate with or even
know the existence of other KSs.
• Blackboard: Blackboard is the place where the specialists work
together to find the solution . The formal definition of the blackboard
is "a globally accessible database which is used for intermediate,
partial results of problem-solving ". Each KS can read and write the
shared blackboard.
• Controller: The controller decides "which knowledge source to
execute next in runtime for optimal problem solution“.

3. Blackboard Architecture
Controller
Knowledge
Sources
Blackboard

4. • Applicable problems:
– Complex problems where information is ambiguous
– A large problem consisting of smaller sub-problems
– A problem with many different solutions
• Resilience to change:
– When new knowledge sources are added, the other
components of the system are not affected.
– If new information is added to the problem, new knowledge
sources can easily be added.
– There are no dependencies between knowledge sources, so
they can easily be put in, taken out, or swapped.
• Negative behavior:
– The difficulty of testing: Because of the non-deterministic
nature of the blackboard architecture, the solution of each
execution may not be consistent.
– Single point of failure: If the blackboard crashes, the whole
system will stop working because none of KSs are able to
access the memory to solve the problem.

5. • The blackboard approach to organizing a large program was first
presented in the HEARSAY-II research.
• HEARSAY-II was a speech understanding program; it was initially
designed as the front end for a library database of computer
science articles.
• The user of the library would address the computer in spoken
English with queries such as, “Are any by Feigenbaum and
Feldman?” and the computer would answer the question with
information from the library database.
• Speech understanding requires that we integrate a number of
different processes like Signal processing; recognition of
phonemes, syllables, and words; syntactic parsing; and semantic
analysis.
• The blackboard architecture allowed HEARSAY-II to coordinate
the several different knowledge sources required for this
complex task.

6. • KS1 – the waveform of the acoustic signal
• KS2 – the phonemes or possible sound segment of the acoustic
signal
• KS3 - The syllables that the phonemes could produce.
• KS4 – try to generate possible word sequences
• KS5 – puts the word sequence into possible phrases