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 • “chunk”of 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 “chunk”after 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