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Formalizing TV Crime Series: Application and Evaluation of the Doxastic Preference Framework Kevin M. van Andel 5686199 Bachelor thesis Credits: 9 EC Bachelor Opleiding Kunstmatige Intelligentie University of Amsterdam Faculty of Science Science Park 904 1098 XH Amsterdam Supervisor Prof. dr. Benedikt Löwe Institute for Logic, Language and Computation (ILLC) Faculty of Science University of Amsterdam Science Park 904 1098 XH Amsterdam June 25th, 2010 Abstract We aim at capturing the human notion of story understanding in a formal system. We apply a formal system, the Doxastic Preference Framework (DPF), to seven narratives from four episodes of CSI: Crime Scene In- vestigationTM. From an analysis of the formalizations we reach similar conclusions as in previous work. That is, all the formalizations of this commercial TV crime series consist of a small number of specific struc- tures called building blocks, and we identify a number of deficiencies and missing features in DPF. To illustrate the difficulty of proposing an experimental setup for human story understanding, we present a small experiment to verify whether two stories that are different in their formal structure, are also perceived as different by human subjects. Ideally, we want to know how well DPF captures the notion of human story under- standing. For this we refer to an existing proposal for an empirical eval- uation on the basis of comparison of two formal frameworks. Finally, we discuss future work on this subject. Keywords — formal frameworks, formalization, isomorphism, logic, story understanding ii Contents 1 Introduction1 1.1 Motivation...................................1 1.2 Related work.................................1 1.3 Overview...................................2 2 Formalization of narratives3 2.1 Methodology.................................4 3 The formal frameworks5 3.1 The Plot Units Framework..........................5 3.2 The Doxastic Preference Framework.....................7 4 Formalization of narratives from CSI episodes in DPF 10 4.1 CSI: Crime Scene InvestigationTM ...................... 10 4.2 Formalizations and analysis.......................... 10 4.2.1 Trick roll............................... 10 4.2.2 The killed house guest........................ 11 4.2.3 Winning a fortune.......................... 12 4.2.4 Faked kidnapping........................... 12 4.2.5 Hit and run.............................. 14 4.2.6 Pledging gone wrong......................... 15 4.2.7 The severed leg............................ 15 4.3 Identifying deficiencies in DPF........................ 16 5 Evaluating formal frameworks 17 5.1 An experiment on human story understanding................ 17 5.1.1 Experimental setup.......................... 17 5.1.2 Results................................ 18 5.2 Methods to compare formal frameworks................... 18 6 Conclusion and discussion 18 6.1 Discussion................................... 19 6.1.1 Improving DPF............................ 19 6.2 Future work.................................. 20 A Timeline of narratives from CSI episodes 22 A.1 Episode 1: Pilot................................ 22 A.1.1 Trick roll............................... 22 A.1.2 The killed house guest........................ 22 A.2 Episode 2: Cool Change........................... 23 A.2.1 Winning a fortune.......................... 23 A.3 Episode 3: Crate ’n Burial.......................... 24 A.3.1 Faked kidnapping........................... 24 A.3.2 Hit and run.............................. 24 A.4 Episode 4: Pledging Mr. Johnson....................... 25 A.4.1 Pledging gone wrong......................... 25 A.4.2 The severed leg............................ 26 iii 1 Introduction 1.1 Motivation Humans are generally good at understanding stories. So far we have not been able to capture the human notion of story understanding in a formal representation. So what we are inter- ested in is to capture this notion and to represent it formally. If we know how to tackle this problem, we might be able to empirically identify the structures of a narrative that may be suited in particular genres or even interesting for a specific public. From a more global per- spective, we are interested in the question whether two stories are identical in structure with respect to a fixed formal framework, and whether this formal notion of identity corresponds to the informal human notion of identity of stories. While capturing the human notion of story understanding is what we actually want to do, it is a topic beyond the scope of this thesis. We do not have a formal framework that captures this notion, let alone an algorithm that automatically produces formalizations in this framework. We discuss a variety of other applications and topics that are beyond the scope of this thesis in Section 6.2. What we will discuss in this thesis with respect to story understanding, is the application and evaluation of a formal framework called the Doxastic Preference Framework (DPF) (Löwe and Pacuit(2008), Löwe et al.(2009), Löwe(2010)) and to propose a number of suggestions on how to improve this formal framework. Before we specifically discuss this, we will give an overview of the work that is related to the topic of story understanding. 1.2 Related work The available literature on story understanding is vast. We attempt to focus on literature that devotes itself to the topic of formalizing texts. Some of the research done in the field of story understanding is creating computer algorithms that are able to perform an analysis of stories automatically, given a narrative in a natural language, or more specifically produce formal representations of such narratives. Correira(1980) discussed the task of parsing narrative texts. He emphasized on the difficulty of this task, from parsing single sentences to paragraphs or longer texts, where knowledge that goes beyond the narrative is required in order to understand it. Kazantseva and Szpakowicz(2010) presented an approach by which summaries can be automatically created from short literary stories. Story grammars, which fall in the same category as the formal frameworks that are dis- cussed in this thesis, base their formalizations on rewrite rules. Black and Wilensky(1979) proposed an evaluation of story grammars, and argued that they are not useful for story understanding. Rumelhart(1980) countered their arguments by bringing to light their mis- understandings on story grammars and their failure to stress the true problems that underly story grammars. Following this paper, Frisch and Perlis(1981) suggested a proper method to analyze and evaluate story grammars. While proposing a computer algorithms for narrative formalization is beyond the scope of this thesis, a formal framework has to be defined first, that adequately captures the rel- evant structures of a narrative, that correspond to the notion of how humans understand stories. On a similar note, we are also interested in finding the relevant structures of a narra- tive for a specific genre or audience. In a paper on story understanding by van Dijk(1980), he discusses the role of psychology in narrative theory and particular important results in that field or research. Experiments on story understanding were done by Bower(1976), focusing specifically on how humans represent stories in memory. Automated story synthesis engines could use the relevant structures to synthesize stories interactively in computer games. For example, Young(2007) proposes a basic approach to modeling narratives in interactive virtual worlds. Intelligent agents in computer games could employ their reasoning based on their beliefs about the preferences about other agents, 1 including human agents. Agents may change their beliefs about other agents or even their preferences as the story progresses. An example of a story synthesis engine is Mexica, which was proposed by Pérez y Pérez and Sharples(2001). However, Mexica does require human guidance to produce stories. Their model is based on the engagement-reflection style of writing. That is, according to Pérez y Pérez and Sharples(2001), creative writing is a cycle of engagement and reflection. Narratives are composed of two main features: story and discourse. As in the model from Young(2007), both these features are distinctive parts of a narrative. With respect to the central topic of this thesis, we have to distinguish story and discourse as well during the formalization process. We particularly focus on the storyline in order to create formaliza- tions in DPF. Lehnert(1981) proposed a formal framework for the conceptualization of narratives based on how humans summarize them, i.e. how humans represent such summaries inter- nally in memory. We can refer to this framework as the Plot Units Framework (PUF) and it is part of the discussion in this thesis. More recent developments in formal framework research comes from (Löwe and Pacuit, 2008), who proposed DPF. They pursued the goal of “formalizing and understanding rea- soning processes in multi-agent situations with imperfect information”. They particularly focused on the actual behavior of agents. Because DPF is the central topic of this thesis, we leave further discussion to the remainder of this paper. Humans are able to analyze narratives and make judgements about the beliefs and pref- erences of characters in a narrative quite easily (Löwe, Pacuit and Saraf, 2009). More of the motivation from the previous subsection can be found in that paper as well. From Section 4 of (Löwe, Pacuit and Saraf, 2009) we partly reused

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