A Survey on Story Generation Techniques for Authoring Computational Narratives <s> 4) Case-Based Reasoning: <s> Telling a story is a difficult task that requires a variety of knowledge and cognitive processes: knowledge about themes, writing techniques, the story world, and presentation; processes such as planning, problem-solving, recall and creativity. This dissertation presents a model of the storytelling process which incorporates theories of creativity, memory and author-level planning. This model has been implemented in a computer program called MINSTREL which tells short, theme-based stories about King Arthur and his Knights of the Round Table. ::: MINSTREL's creativity process is based upon creativity heuristics called Transform-Recall-Adapt Methods (TRAMs). Each TRAM integrates a simple problem transformation which searches the problem-space for new knowledge to apply to a problem with a corresponding adaptation which can adapt any discovered knowledge to the original problem. By using TRAMs to augment the problem-solving process, MINSTREL is able to invent useful new problem solutions. By incorporating creativity into the recall process, MINSTREL makes creativity available to any cognitive process, and permits the use of multiple TRAMs to make creative "leaps". ::: MINSTREL's storytelling process is based upon a model of author-level problem-solving. In addition to a process model of author-level problem-solving, MINSTREL implements four important classes of author-level goals and plans: (1) Thematic, (2) Dramatic, (3) Consistency, and (4) Presentation. MINSTREL uses these goals and plans to tell a number of short stories in the King Arthur domain. ::: MINSTREL is a computational model of the cognitive processes of storytelling and creativity. MINSTREL (1) describes a process model of storytelling, (2) identifies important storytelling goals and plans, (3) identifies fundamental storytelling processes, (4) describes a process model of creativity, (5) explains how a problem-solver can find and adapt old knowledge to create new solutions, (6) identifies useful creativity heuristics, (7) explains creative "leaps", (8) explains the relation of creativity to problem-solving, (9) describes the relationship between memory and creativity, and (10) integrates creativity into a larger cognitive model. <s> BIB001 </s> A Survey on Story Generation Techniques for Authoring Computational Narratives <s> 4) Case-Based Reasoning: <s> MEXICA is a computer model that produces frameworks for short stories based on the engagement-reflection cognitive account of writing. During engagement MEXICA generates material guided by content and rhetorical constraints, avoiding the use of explicit goals or story-structure information. During reflection the system breaks impasses, evaluates the novelty and interestingness of the story in progress and verifies that coherence requirements are satisfied. In this way, MEXICA complements and extends those models of computerised story-telling based on traditional problem-solving techniques where explicit goals drive the generation of stories. This paper describes the engagement-reflection account of writing, the general characteristics of MEXICA and reports an evaluation of the program. <s> BIB002 </s> A Survey on Story Generation Techniques for Authoring Computational Narratives <s> 4) Case-Based Reasoning: <s> In this paper we present a system for automatic story generation that reuses existing stories to produce a new story that matches a given user query. The plot structure is obtained by a case-based reasoning (CBR) process over a case base of tales and an ontology of explicitly declared relevant knowledge. The resulting story is generated as a sketch of a plot described in natural language by means of natural language generation (NLG) techniques. <s> BIB003 </s> A Survey on Story Generation Techniques for Authoring Computational Narratives <s> 4) Case-Based Reasoning: <s> We discuss the design of the Hybrid Evolutionary-Fuzzy Time-based Interactive (HEFTI) storytelling engine. HEFTI uses genetic algorithms at its core to recombine and evaluate story components generated from a set of story templates. The system allows authors to rely on HEFTI to perform recombination, mutation and selection operations that generate logically congruent variants of the original story via traversal, generation and deletion of (links in) the story elements. <s> BIB004
Gervás et al. generated plots using case-based reasoning with authorial constraints BIB003 . Their work once again makes use of Propp's grammar, and the author's only role is to declare which functions need to appear in the final plot, and the initial state of the space and their roles. The system then adapts pieces of similar plots, ensuring that all functions are included in the new plot and that all the conditions of the functions are met. The final plot is, therefore, a mixture of several similar story plots, with the roles filled by the space provided by the author. MINSTREL BIB001 is a complex plot generator which aimed at modeling creativity and even modeled a form of author intent by providing each story with a moral message, which must be conveyed through the generated plot. The stories created in MINSTREL were limited to singular stories which were about half a page in length. MINSTREL was again dependent on a large volume of manual authoring in terms of the space of the story. The system did, however, use a detailed model of individual character goals, beliefs, and desires in conjunction with its authorial intent, so that the resulting plots make sense with respect to their emotional and physical effects on the characters in the story space. Furthermore, new events could be created by recalling and modifying past events used in the generation process. MEXICA BIB002 uses a cognitive model of creativity to formulate a story by piecing together a number of plot fragments, which are constrained by a set of pre-and postconditions. The system makes use of previous stories, taking them as input to evaluate and reflect upon the current story being generated. In MEXICA, characters, and specifically relations between characters, are explicitly modeled. The plot is incrementally built by examining potential new events, each event having preconditions relating to patterns that must exist inside the space. 5) Genetic Algorithms: HEFTI BIB004 uses a genetic algorithm approach to narrative generation. In this system, the author must specify a basic structure, or "story thread" which must be met by the plot. The fitness of a story is determined by the events, each of which must be rated by the author based on their like/dislike of a given event. The genetic algorithm thus attempts to achieve the best possible result according to the author's ratings while still ensuring that the requirements of the story thread are met. This genetic algorithm is also used to modify the plot if there are any interactor deviations. Although this section presented a number of different approaches to the generation of plot, each approach followed a basic principle that using constraints is a means of enforcing a certain level of quality or intent. Tighter constraints lead to a more limited set of stories, for example, the grammar-based plot generators are often restricted to creating stories in one particular genre. Looser constraints allow for more story variance and are often used to guide the generation process rather than explicitly control it. This often leads to a greater diversity of stories, and in interactive stories, this is used to encourage multiple experiences of the work. Tighter constrains, however, produce more reliable results and allow for more nuanced or subtle changes in the plot.