CMU CS 15-675 Architectures for Software Systems Spring 1998
Blackboard Systems
with answers
Garlan & Kazman Questions on Readings for Lecture 20 Due: Wed Mar 30, 1998
The papers:
[SG95]: Shaw & Garlan: Software Architectures book, Sections 2.6-2.7, 3.5
[Nii86]: Blackboard Systems, Parts 1 and 2
Hints:
Section 2.6 and 2.7 introduce two more architectural styles. Section 3.5 uses the model of 2.7 to explain Nii's elaboration of 2.6.
Read the Nii paper first and foremost to understand the blackboard model and the kinds of problems for which it is appropriate. Study Hearsay and Hasp to see how the model is realized in two rather different settings, but don't get embroiled in fine details. Look at the other examples to see the range of variability available within the basic framework. Concentrate on the computational relations between the knowledge sources and the blackboard data structures. Notice the differences in control strategies, but -- again -- don't get bogged down in the details.
Questions:
1) In a few lines, describe the components of the blackboard model.
Blackboard has three major components: knowledge sources, blackboard data structure, and control.
Knowledge sources partition domain knowledge; they contribute independently to solving the problem, can be represented in many ways, interact only via the blackboard, and encode their conditions of applicability.
Blackboard data structures provide highly-structured hierarchical representation for objects that are intermediate and final results
Control provides opportunistic processing by monitoring blackboard changes.
2) What are major differences between the Hearsay-I and Hearsay-II systems?
Domain
: Hearsay-I was restricted to chess. Hearsay-II was domain independent.Control strategy: In Hearsay-I knowledge sources are invoked "in lock step" (a built-in problem solving strategy) via the overlord. In Hearsay-II they are invoked opportunistically via a blackboard monitor and scheduler.
Knowledge source structure: Hearsay-I had only a single level of representation (the word level). Hearsay-II had 6-8 levels, ranging from acoustic/phonetic to phrases/sentences.
Modified: 5/21/98