12-10-2013_09-24-50 / [Simon_Kendal,_Malcolm_Creen]_Introduction_to_Know(BookFi.org)

Procedures, and the Constraint Dependency Relations to compute the Constraint Results.

The SELECT VIOLATED CONSTRAINT chooses one violated constraint to be revised. The inference uses the Constraint Results and the Fix Dependency Relations to generate one Selected Violated Constraint.

The REVISE inference remedies a violated constraint. The inference uses the Selected Violated Constraint, Fixes and Fix Procedures to repair the constraint violation, and to propose new Parameter Values (Coelho and Lapalme, 1996).

As implemented in the SALT software (SALT—a knowledge-acquisition tool for propose-and-revise using a role-limiting approach) there are three types of knowledge roles:

procedures to assign a value to a parameter, which would result in a design extension

constraints that could be violated in a design extension

fixes for a constraint violation.

The user can enter one of the three types of knowledge: PROCEDURE, CONSTRAINT and FIX. For each type of knowledge, a fixed menu (or schema) is presented to the user (in SALT’s case a domain expert) to be filled out.

An example of the information provided by a user for a constraint is as follows (from [Marcus and McDermott, 1989]):

Reusing PSMs and Reusing Domain Knowledge

Problem-solving methods can be reused on other similar problems in different domains. For example, the general process of designing a car may be very similar to the general process employed when designing a house. Thus the PSM may be reused for other design tasks.

Furthermore, different PSMs for different problems can potentially use some of the same domain knowledge. For example, a knowledge of electronics and electrical components within TVs can be used by a PSM to fix faults in current TVs. This

domain knowledge can be used by another PSM to design new TVs. Thus domain knowledge can be reused for different applications.

Activity 6

This activity will help you extend your understanding of the concept of reuse in relation to PSMs.

Visit the Internet Reasoning Service at: http://kmi.open.ac.uk/projects/irs/

Produce a set of brief notes on the types of reuse described there.

Feedback 6

Your notes should clearly distinguish:

direct reuse

parameterised reuse

generic plug and play.

Genericity or Ease of Use?

To enable reuse we need to develop a library of PSMs. However, these are often difficult to classify, as we need to specify the:

genericity, i.e., the task independence

formality

granularity, i.e., the scale of the PSMs contained within the library.

Furthermore, there is a usability/reusability trade off to consider.

Activity 7

Consider the following scenario. You have at your disposal two very successful professional designers.

Person A has successfully designed a wide range of things: houses, bridges, gardens and even a railway station but they have never designed any electrical device.

Person B has successfully designed: HiFi, MP3 payers, digital cameras and computers but all they have ever designed is electrical equipment.

Which person would you choose to design a new plasma screen TV?

Which person would you choose to design a museum?

Feedback 7

When it comes to choosing the best person for the job you have to consider which one has the most appropriate knowledge.

For the task of designing the plasma screen TV you presumably choose person B. Even though they have never designed a TV before they clearly have a detailed knowledge of electrical systems, having already designed a range of electrical devices.

For the task of designing a museum you presumably choose person A. Person B is a very successful designer however they have never designed anything except electrical equipment. Person A has had a very varied design career. Even if they know nothing about museums they can draw on a wide range of experience. Presumably before designing the museum they will need to find out about museums and they may need to expand their design knowledge slightly. For example, they may need to learn how to design crowd control spaces.

This scenario demonstrates an important concept: the issue of generic knowledge verses ease of reuse. Person A has a generic design knowledge that can be reused in a wide range of situations, however before it is reused it may need adapting/updating. Person B can easily reuse their knowledge, without the need for adaptation, however this knowledge is more focused, i.e., less generic, and therefore can only be reused in a limited range of situations.

Task-independent PSMs will require refinement and adaptation before they can be used but can be reused in a wide range of situations.

Task-dependent PSM may require little or no adaptation but can only be reused in some circumstances.

A very generic design PSM, i.e., a task-independent PSM, may be used to design houses, cars and clothes. However, because it is a very generic PSM, it may need to be refined for each task before use. In contrast, a task-dependent PSM created specifically for designing electrical equipment may be used to design TVs, DVDs or computers without any adaptation but would not be appropriate for other design tasks such as designing houses or gardens.

The use of PSMs has one significant advantage over the use of blackboard architectures, namely they promote reuse. By separating control knowledge from domain knowledge reuse of both is enabled.

Activity 8

Consider the following scenario. A KBS is created for a car mechanic to diagnose faults in a range of cars. This system is created with the control and domain knowledge as separate components. Thus we have:

The process of fault finding i.e. control knowledge

Knowledge of cars i.e. domain knowledge

Identify other situations in which we can reuse the control knowledge.

Identify other situations in which we can reuse the domain knowledge.

Feedback 8

By plugging in knowledge of other equipment such as mobile phones or computers the control knowledge can be reused to make other fault-finding KBS. These could be used by other technicians.

By creating a control method to describe the process of designing equipment the domain knowledge of cars can be reused to create a KBS that designs cars.

Limitations of PSMs

The limitations of PSMs include:

To enable reuse we need to develop a library of PSMs. However, PSMs are difficult to classify. We need to specify the genericity (task independence) and granularity (size).

There are reusability—usability trade offs to consider. Task-independent PSMs will require refinement and adaptation before they can be used. They can however be reused in a range of situations. Task-dependent PSMs require little adaptation before use, but they are less easily used elsewhere.

Summary

This section has provided an introduction to how KBSs can be supported with separate libraries of PSMs.

Web Links

Generic Task Toolset http://www.cis.ohio-state.edu/lair/Projects/GTToolset/toolset.html

IBROW http://swi.psy.uva.nl/projects/IBROW3/home.html

KEML ftp://swi.psy.uva.nl/pub/keml/keml.html

Protege http://smi-web.stanford.edu/projects/protege/

Sisyphus III http://www.psyc.nott.ac.uk/research/ai/sisyphus/

VITAL http://kmi.open.ac.uk/ john/vital/vital.html

Self-Assessment Questions

Question 1

Contrast the reusability of task-dependent and task-independent PSMs.

Question 2

Describe the role of the following three inferences in the P&R PSM:

propose

check

revise.

How does the select parameter inference function?

Suggested Solutions

Answer 1

Task-independent PSMs require refinement and adaptation before they can be used but they can be reused in a range of situations.

Task-dependent PSMs require little adaptation before use but they are less easily reused elsewhere.

Answer 2

The PROPOSE inference computes the value of the selected parameter.

The CHECK inference verifies the constraints after computing parameter values. The REVISE inference remedies a violated constraint.

The SELECT PARAMETER inference chooses one parameter to have its value computed and uses the Input Parameters, the Parameter Values already computed and the Parameter Dependency Relations to obtain a Selected Parameter.

SECTION 4: KNOWLEDGE ACQUISITION DESIGN SYSTEM (KADS)

Introduction

This section provides an explanation of the KADS methodology.

Objectives

By the end of the section you will be able to:

describe KADS.

Understand how KADS is an example of a PSM.

Purpose of KADS

In general information systems development, there are many methodologies that can be used to provide an overall control of that development.

Within KBS development however, there was no overall design strategy for a considerable time.

Activity 9

This activity will draw on your knowledge of information systems development to help you anticipate the need for something significantly different in relation to methodologies for KBS development.

Considering the process of developing an information system, what factors might make it difficult to directly apply such methodologies to the development of KBSs?

Feedback 9

You should have been able to recognise that most information systems are concerned with data and KBSs are concerned with knowledge. Data is generally much more accessible—being stored in databases of one kind or another, whereas knowledge is stored in the minds of experts.

Knowledge-based systems also tend to be more complex. Information systems often perform numerical calculations which have a correct answer, e.g. a worker who works for 10 hours for £10 per hour should get paid £100. £99.99p while very close would be an incorrect answer. A KBS on the other hand simulates a human being making decisions. While decisions can be good decisions or bad decisions they cannot usually be clearly categorised as right or wrong. For example, when choosing a university course, clearly some courses are in a subject that will interest the student more than others and some will lead to qualifications that will enable a graduate to find work more easily than others. Taking these factors into account you may choose to do a degree in computing. If you are not reasonably able in mathematics doing an engineering degree may be a poor choice for you—but this decision could not be clearly categorised as a wrong decision. Thus checking the quality of the outputs from a KBS is much more difficult than checking the outputs from an information system.

The KADS is an attempt to overcome this difficulty by providing a system for knowledge engineers and ES developers to follow.

Knowledge acquisition design system aims to solve two specific problems in KBS development:

Firstly, large-scale problems could not easily be solved by one knowledge base— especially if it was restricted to one knowledge representation scheme—and which was very inefficient to run and difficult to maintain. This was overcome by the development of blackboard architectures and the same principle of segmented knowledge bases is supported by KADS.

Secondly, the benefits of explicitly separating control and the domain knowledge became clear as the modelling approach was adopted, and thus the KADS methodology was developed as a problem-solving methodology (see previous section).

Knowledge acquisition design system, and its more recent variant, CommonKADS, is the most commonly used methodology within Europe for the development of KBSs. KADS is the most prominent example of a PSM-based methodology, thus discussions in the previous section apply to KADS.

Knowledge Acquisition in KADS

The KADS approach includes the following knowledge acquisition activities:

Elicitation—eliciting the knowledge

Analysis—interpreting the knowledge

Formalisation—formalising the knowledge so that it can be used in a computer.

Before KADS, there was an approach to knowledge acquisition that consisted simply in:

acquiring domain knowledge

transferring knowledge (somehow) to a KBS.

In this approach the experts reasoning process was not modelled—it was left to the inference engine to determine if/when to apply the knowledge.

The KADS approach treats the knowledge-acquisition process as a modelling activity, i.e., the expert’s problem-solving knowledge is modelled, among other models, this leads to the efficient application of domain knowledge and allows reuse of control and domain knowledge.

Multiple Models in KADS

Based on the ideas of modelling the PSMs, KADS supports the development of various models. These include:

Process or organisation model, where the processes within the organisation are modelled in order to assess the role and impact of the KBS. This reduces the friction that may occur when trying to implement the KBS within the organisation.

Expertise model, models the problem solving or expert behaviour required of the system. Knowledge acquisition design system libraries of reusable PSMs have been created to support prediction, assessment, design, planning and schedule tasks.

Activity 10

This activity involves you in discovering the characteristics of some of the other models used in KADS.

Other models that may be used in the KADS approach include:

Application model—defines the functions of the system with respect to users

Task model—defines the tasks that the KBS must perform

Cooperation model

Conceptual model

Design model.

1.Search the Internet for documents relating to the last three of these models.

2.Make brief notes on their purpose.

Feedback 10

You should have been able to locate documents describing the models as follows:

Cooperation model—specifies how subtasks in the task model should be done if cooperation is necessary. This model would need to be applied if, for example, the solution of a problem by the system required information from the user.

Conceptual model—this is essentially a combination of the models of expertise and cooperation as these together specify the overall behaviour of the system. Such a model would be based on abstract descriptions of the objects and operations that the system needs to know about.

Design model—specifies how to implement the system in the form of descriptions of computational and representational techniques as well as hardware and software requirements.

Theses models essentially represent steps in defining the goals of the KBS development.

Some of the advantages of this multiple model approach in KADS are that those involved in the development of the KBS can more easily identify, describe and select characteristics of the targeted system as well as focus on specific aspects while ignoring—at least for the moment—other components.