The CommonKADS Design Model

1
The CommonKADS Design Model

• Introduction to CommonKADS
• CommonKADS Design Model
• Worked Example
• Conclusion

2
Introduction to CommonKADS

• Problem faced by Knowledge Engineers
• --designing good KBS relies on knowledge
  engineer abilities
• Approach to the problem--CommonKADS
• --represent the expert knowledge and design
  specification in form of text or diagrams
• Important components of CommonKADS
• --Expertise Model domain knowledge,inference
  knowledge, task knowledge
• --Design Model

3
The CommonKADS Design Model

• Intends to support knowledge engineers in
  choosing knowledge representations and
  programming techniques
• Three-stage transformation process
• --Application design
• --Architectural design
• --Platform design

4
Application Design

• Purpose is to decompose the knowledge into
  manageable chunks
• Three approaches
• --Functional decomposition
• --Object-oriented decomposition
• --AI paradigms

5
Functional Decomposition

• Treat each inference step from the Expertise
  Model as a chunk of functionality
• Benefits
• --replicate expert problem solving process
• --canonical inference has its expected
  functionality already defined
• --preserve task structure

6
Object-oriented Decomposition

• Treat each concept from the domain model as a
  chunk of data--an object class
• Preserve the structure of the domain models in
  the expertise model
• inference and task structure may be maintained
• Have difficulty in assigning production rules
  because they refer to more than one objects

7
AI Paradigm

• Include blackboard system, constraint-based
  programming, qualitative simulation, or
  model-based reasoning
• chunkof knowledge may be constraints, knowledge
  sources, or whatever appropriate for the chosen
  approach
• little of the structure of the expertise model
  will be maintained

8
Architectural command

• Characterize the contents of each chunkafter
  decomposition to specify further design
  requirements
• A function name that describe the action which
  the function performs
• --e.g. an inference step of type select-subset
  can be implemented by a subset command
• Help validate the Expertise Model

9
Architectural Design

• Task is to define a computational infrastructure
  capable of implementing the architecture commands
  defined in the application design
• Emphasis is on choosing ideal techniques
• Experience of knowledge engineer can play an
  important role

10
Platform Design

• Consider how the ideal knowledge representation
  and inference techniques should be implemented in
  chosen software
• Knowledge representation is not a problem
• Some programming techniques may be awkward to
  implement

11
Worked Example I IMPRESS

• Diagnose faults in machine
• Application design functional decomposition
• Architectural design
• --knowledge representation objects
• --inference step production rules,
  object-based operations
• Platform design KAPPA-PC on Compaq 386
• Flow of control based on task structure from the
  Expertise Model

12
Worked Example II X-MATE

• Assess the ability of mortgage applicants
• Application design functional decomposition
• Architecture design select data source, use
  production rules, choose rule set, use arithmetic
  functions
• Platform design KAPPA-PC 1.1 on HP Vectra 386 PC
• Flow of control repeat running through the whole
  inference structure

13
Conclusion

• CommonKADS provides useful documentation of
  system design process
• Encourage greater modularity and reusability of
  designs
• Help to validate the Expertise Model
• Weakness
• --lack of guidance on selection of techniques
• --lack of a defined set of architectural
  commands