Narrative Composition: Achieving the Perceived Linearity of Narrative

Pablo Gervas´ Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain [email protected]

The last few years have seen an increased in- language to the task of generation, and what was terest in narrative within the field of Natural Lan- known about language from a computational point guage Generation (Reiter et al., 2008; Elson and of view concerned simple texts. Most of the stud- McKeown, 2010; Siddharthan et al., 2012; Lester, ies on language and computation had applied sim- 2012). Narrative is generally acknowledged as a ilar simplifying assumptions. However, such re- fundamental mode of presenting and communicat- stricting assumptions are no longer necessary and ing information between humans, with different may be inhibiting progress. In terms of technol- manifestations across media but with a very signif- ogy, the field has matured significantly over the icant presence in textual form. Yet efforts in Nat- intervening years. The current state of the art pro- ural Language Generation research have generally vides a wide range of solutions that may be well side stepped the issue. Aside from the pioneer- suited to address some of the more complex phe- ing work of (Callaway, 2002) and an early attempt nomena involved in literary text. Additional ob- to bridge the gap between narratology and natu- jections may be made on the grounds that we do ral language generation (Lonneker,¨ 2005), the field not know enough about these phenomena. Such had mostly avoided narrative until recent times. objections, however valid they might have been Two possible arguments may be considered as an originally, are no longer valid either. Many of explanation of this: one based on the need to re- the phenomena that were considered beyond com- strict initial work within a field to the simpler chal- putational treatment (metaphor, emotion, tempo- lenges before tackling the difficult ones, and an- ral reasoning, dialogue...) have been the subject other based on an assumption that the peculiarities of serious and sustained study over the same time of narrative have already been covered by existing period. Many approaches to their computational work. Both arguments can be shown to be inap- modelling and treatment have become available. propriate. More to the point, the last few years have seen With respect to the first argument, the field of a rise of interest on literary text within the natu- natural language generation has for many years ral language processing community. This is ev- operated under the tacit assumption that state of idenced by the number of workshops addressing the art technology can only aspire to generating topics related to literature: Workshop on Com- texts within a limited range of domains and genres. putational Approaches to Linguistic Creativity at These have over the years been defined in different NAACL HLT 2009 and 2010, Computational Lin- ways, but in spite of changes, literary texts have guistics for Literature Workshop at NAACL HLT usually been considered to be outside the range 2012 and 2013, Computational Models of Narra- of possible candidates. From an engineering point tive events held as AAAI Fall symposium in 2010, of view, this kind of restriction made sense when as LREC workshop in 2012, and as satellite work- the field was starting, for two important reasons. shop of CogSci 2013, just to name a few. One, the technological solutions available at the With respect to the second argument, the recent time for the various tasks involved in natural lan- reappearance of narrative as a research topic for guage generation were in their infancy, and the lin- NLG should be enough to dispel the notion that guistic complexity of literary text might have been all its problems have already been solved. Narra- beyond their scope. Two, natural language gener- tive has many peculiarities that set it apart from ation arose from a desire to extend the studies that other kinds of text, and the body of work address- had been carried out for computational analysis of ing narrative as a research topic within NLG has

103 Proceedings of the 14th European Workshop on Natural Language Generation, pages 103–104, Sofia, Bulgaria, August 8-9 2013. c 2013 Association for Computational Linguistics at most uncovered and staked out a set of prob- discuss the relation of the task of narrative compo- lems and challenges that area waiting further ex- sition with a number of existing research problems ploration. Of these various open problems in the such as story generation (which could correspond treatment of narrative, my talk will focus on the to the construction of fabula but is sometimes sim- problem of narrative composition. plified down to construction of a discourse di- rectly) and creativity (which has been addressed Research on narrative is plagued by the diffi- with respect to story generation but may also con- culty of establishing a definition of the term that stitute a fundamental ingredient of the composi- is both sufficiently formal to act as foundation for tion task). scientific rigour, and sufficiently rich to cover the fundamental aspects that people associate with the Acknowledgments term. At the present stage of development, tenta- tive definition need to be established, to be later The work on which this talk is based was partially confirmed on the basis of empirical work and suc- supported by the Ministerio de Educacion´ y Cien- cesful evaluation of results. The talk will out- cia (TIN2009-14659-C03-01). line some of the possibilities that must be con- sidered (arising from established definitions in the References field of narratology) and some of the restrictions that arise from the computational nature of the Charles B. Callaway. 2002. Narrative prose genera- task. From the combination of these constraints, tion. Artificial Intelligence, 139(2):213–252. a working model of narrative structure will be out- David K. Elson and Kathleen R. McKeown. 2010. lined. However, it is clear that such a model must Tense and aspect assignment in narrative discourse. document the relation between a semantic descrip- In Proceedings of the 6th International Natural Lan- guage Generation Conference, INLG ’10, pages 47– tion of the content of the narrative (what is usually 56, Stroudsburg, PA, USA. Association for Compu- termed the fabula) and its rendition as a sequential tational Linguistics. discourse. The task of narrative composition will be specified as the task of constructing such a dis- James Lester. 2012. Expressive nlg for next- generation learning environments: language, affect, course (or discourse plan) for a given semantic de- and narrative. In Proceedings of the Seventh Inter- scription of fabula. This discourse should be sus- national Natural Language Generation Conference, ceptible of being converted into text and it should INLG ’12, pages 2–2, Stroudsburg, PA, USA. Asso- appropriately conveys the set of events in the fab- ciation for Computational Linguistics. ula in such a way that satifies a number of tra- Birte Lonneker.¨ 2005. Narratological Knowledge for ditionally accepted requirements (like having an Natural Language Generation. In Graham Wilcock, identifiable theme, a certain temporal and causal Kristiina Jokinen, Chris Mellish, and Ehud Reiter, coherence, a recognisable set of characters...). A editors, Proceedings of the 10th European Workshop on Natural Language Generation (= ENLG 2005), number of basic narratological concepts will be pages 91–100, Aberdeen, Scotland, August. described where they provide tools for breaking down the task into computationally tractable sub- Ehud Reiter, Albert Gatt, Franc¸ois Portet, and Marian van der Meulen. 2008. The importance of narra- problems. Of particular interest is the concept tive and other lessons from an evaluation of an nlg of focalization, which is used by narratologists to system that summarises clinical data. In Proceed- describe the way certain segments of a narrative ings of the Fifth International Natural Language follow a particular character, and which provides Generation Conference, INLG ’08, pages 147–156, Stroudsburg, PA, USA. Association for Computa- a useful computational representation of both the tional Linguistics. granularity and the shift in focus employed during the process of converting the semantics of the fab- Advaith Siddharthan, Matthew Green, Kees van ula into a linear discourse. Deemter, Chris Mellish, and Rene´ van der Wal. 2012. Blogging birds: generating narratives about As part of the talk, narrative composition will be reintroduced species to promote public engagement. framed in terms of the accepted task breakdown In Proceedings of the Seventh International Natural Language Generation Conference, INLG ’12, pages for natural language generation, considering that 120–124, Stroudsburg, PA, USA. Association for it may involve a combination of content determi- Computational Linguistics. nation and discourse planning that cannot be seg- regated into separate subtasks. The talk will also

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