Generic Tasks

by

Ihab M. Amer

Graduate Student

Computer Science Dept.

AUC, Cairo, Egypt

Agenda

• Introduction

• Generic Tasks

› Definition

› Main Concept

› Some GTs and their Specs

› Generic Task Tools

› GTs as Building Blocks

• Conclusion

Introduction

• Weakness of the (Rule, Frame, and Logic) Level

› It assumed that there is something called domain knowledge that needs to be acquired quite independent of the problems one might wish to solve, , so it did not distinguish between different types of knowledge-based reasoning.

› This contradicts the interaction problem.

The Interaction Problem

“representing knowledge for the purpose of solving some problem is strongly affected by the nature of the problem and by the inference strategy to be applied to the knowledge.”

• It States that

The shortage in these systems encouraged scientists to present a higher level methodology in KBS named as Generic Tasks (GT). The relationship of the constructs at the generic task level to the rule-frame-logic level is analogous to that between high-level programming languages and assembly languages in computer science.

Introduction (cont’d)

Generic Tasks

• Definition

› Generic tasks are simply, basic combinations of knowledge structures and inference strategies that are powerful for dealing with certain kinds of problems.

Main Concept

• Notice here why we used the term “Type”.

• The appearance of generic tasks is considered to be a good step in satisfying the interaction problem, since each problem type has a distinct strategy type that uses a distinct knowledge type to solve it.

Main Concept• The appearance of generic

tasks is considered to be a good step in satisfying the interaction problem, since each problem type has a distinct strategy type that uses a distinct knowledge type to solve it.

• Notice here why we used the term “Type”.

• This may be clear in the opposite figure:

Some GTs and there Specs

There are several types of generic tasks. They are developed for problems that may frequently appear and need solution. Here, we briefly describe some of them in order to recognize the importance of the GT concept.

Hierarchical Classification

• Input: Given a situation description in terms of features.

• Output: Classify it as specifically as possible, in a classification hierarchy, determining what categories or hypotheses apply to the situation.

• Inference & Control: The establish-refine strategy specifies that when a hypotheses is confirmed or likely (the establish part), its subhypotheses (children of the node) should

be considered (the refine part). If a hypotheses is rejected, its subhypotheses are also ruled-out.

• Example Use: Medical diagnosis can be often viewed partly as a classification problem.

GT Hypothesis Matching • Input: Given a concept (a hypothesis) and a set of data (features) that describe the

problem state.

• Output: Decide how well the concept matches the situation.

The task is a form of recognition. • Inference & Control: At each level, a degree of confidence

in the presence of a feature is computed from the features that constitute evidence for it, and this is performed recursively until a degree of confidence for the concept is computed. The basic theory is that recognition of a complex concept is performed by hierarchically computing intermediate abstractions from

raw data. • Example Use: Recognition can be performed by

means of this strategy. e.g. the concept may be a disease and the data may be the patient data relevant to the disease, and we wish to know what the likelihood of the disease is.

GT Abductive Hypothesis Assembly

• Input: Given a situation description and a set of hypotheses each explaining some aspects of the situation and each with some

plausibility value.

• Output: Construct a composite hypothesis that is the best explanation of the situation.

• Inference & Control: Assembly and criticism alternate. At each stage during assembly the problem solving is driven by an attempt to explain the most significant datum remaining unexplained.

• Example Use: This Task is a diagnostic subtask in diagnostic reasoning as well as in theory formation in science.

Generic Task Tools• Of course researchers needed tools to watch the effect of

using GTs in problem solving. This has pushed them to release some versions for different GT tools. Here we are

going to mention some of them. • CSRL (Conceptual Structures Representation Language) (Bylander & Mittal in 1986) for

hierarchical classification.

• HYPER (HYPothethes matchER)

(Johnson in 1986) for hypotheses matching.

• PEIRCE (named after C. B. Peirce, who first described the form of inference known as abduction.

(Punch, Tanner and Josephson in 1986 ) for GT Abductive Hypothesis Assembly.

GTs as Building Blocks

• Integration between different types of GTs happens in order to solve complex problems.

• If a certain GT needs information which can be available by another one, then it may call it and use its results in a process similar to what happens in modular programming where we find functions calling each other.

• This pushed scientists to develop what we call toolsets, which helps one to build expert systems by using higher level building blocks. Fafner is a release of an integrated toolset, which is available for research use.

•Diagnosis is a problem of finding a cause or set of causes that “best explain” a set of observations of a system, some of them indicating behavioral abnormality.

GTs as Building Blocks (cont’d)

•Diagnosis is a problem of finding a cause or set of causes that “best explain” a set of observations of a system, some of them indicating behavioral abnormality.

GTs as Building Blocks (cont’d)

• The following figure illustrates how integration between various GTs can solve a diagnosis problem.

Conclusion• After the discovery of GTs, solution to different kinds of problems became

much easier.

› For example, to solve a problem, a knowledge engineer needs only choose a GT that is best suited for performing a particular function, or can use different GTs for performing the same function, or can use a combination of them.

› GT facilitates knowledge acquisition because once the KE selects the GT that he will use, his orientation while collecting knowledge will be close to that of the GT (GT proposes a methodology that helps in analysis, design, and construction of a practical knowledge system).

THANK YOU

Ihab M. AmerIhab M. Amer