Understanding Repetition in Natural Language Instructions - The Semantics of Extent

Introduction Natural language instructions, though prevalent in many spheres of communication, have only recently begun to receive attention within computational linguistics[5]. Instructions are often accompanied by language intended to signal repetition of the action that they instruct. In order to develop a system that is able to understand instructions, with the goal of executing them, it is necessary to investigate what is meant by various types of repetition, and the different ways in which repetition can be expressed. We focus on sentences that are instructing that some action is to be performed and that this action is to be performed more than once 1. There are two aspects to consider-scope (what part of the action that is instructed in the dialogue is to be repeated) and extent (how much repetition is to be done). This is illustrated by examples (1) and (2). Place a chunk of rhubarb into each tart. (1) Continue to layer in this way until all the (2) fruit is used. The repetition in (1) has scope on place a chunk of rhubarb (into a tart) and extent across all tarts. (2) has scope over layer in this way and extent until all the fruit used. Within this framework of scope and extent that I have described only informally, I discuss the issue of extent in more detail s. Karlin [3], presents a semantic analysis of verbal modifiers in the domain of cooking tasks. Much of this is pertinent to an examination of extent, in par-tieular the relation of different modifiers to the as-peetual category of an event (according to Moens & Steedman [4]). This has formed an important starting point for my work in understanding instructions for repetition. However, there are aspects where a different approach to Karlin's is required, and some of these are discussed in the rest of this paper.