The Generic/Actual Argument Model

Introduction

The GAAM has been used to model reasoning in copyright law by Stranieri and Zeleznikow (2000a), predict judicial decisions regarding a property split following divorce by Stranieri and Zeleznikow (1998b), support refugee status decision makers by Yearwood and Stranieri (1999), facilitate interactive e-commerce by Yearwood and Avery (Yearwood, Stranieri, & Avery, 2001), implement multi-agent negotiation by Avery and Yearwood (Avery, Yearwood, & Stranieri, 2001), and in determining eligibility for government funded legal aid by Stranieri (Stranieri & Zeleznikow, 2001). Two shell programs that implement GAAM ideas are described in Stranieri and Zeleznikow (2001) and Yearwood and Stanieri (2002).

The GAAM was developed as a framework for modelling discretionary reasoning and has been used to develop practical decision support systems over the last five years. The objective of this chapter is to provide a description of the GAAM in terms of:

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  Identifying the basic set of propositions it supports and how they are combined

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  Identifying the elements that formally control or represent the structure of reasoning

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  Its inference mechanisms and how propositions are derived

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  The extent to which derived propositions are valid and accepted.

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  The way in which it supports discretionary decision making

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  Setting out its capabilities as a non-dialectical model upon which a dialectical model can be built.

The remainder of this chapter is organised as follows: Section 2 sets out how the elements of the GAAM relate to Toulmin argument structures and discusses inferences and the separation of inference from the structure of reasoning. Section 3 presents the GAAM more formally and in detail. Section 4 discusses some of the characteristics of the model, exploring deducibility and possible notions of argument strength and validity. Section 5 compares the model with other approaches.

Argumentation has been used in knowledge engineering in two distinct ways; with a focus on the use of argumentation to structure reasoning (a non-dialectical emphasis) and with a focus on the use of argumentation to model discourse (a dialectical emphasis—See Chapter 5). In contrast, many uses of argumentation for knowledge engineering applications do not model discourse and this corresponds more closely to a non-dialectical perspective.

A non-dialectical representation facilitated the organisation of complex legal knowledge for information retrieval by Dick (1987) and Dick (1991). She illustrates how relevant cases for an information retrieval query can be retrieved despite sharing no surface features if the arguments used in case judgments are represented as Toulmin structures. Marshall (1989), Ball (1994), and Loui, Norman, Altepeter, Pinkard, Craven, Lindsay, and Foltz (1997) have built hypertext based computer implementations that draw on knowledge organised as Toulmin arguments. Hypertext links connect an argument’s assertions with the warrants, backing, and data of the same argument and also link the data of one argument with the assertion of other arguments. In this way, complex reasoning can be represented succinctly enabling convenient search and retrieval of relevant information.