Journal of Robotics, Networking and Artificial Life, Vol. 1, No. 2 (September 2014), 164-168

Integrating the Event Generation Mechanism in the Propp-based Story
Generation Mechanism into the Integrated Narrative Generation System
Shohei Imabuchi

Edogawa-ku, Tokyo, Japan
E-mail: ye66ow@gmail.com
Takashi Ogata

Iwate Prefectural University, Takizawa, Iwate, Japan
E-mail: t-ogata@iwate-pu.ac.jp

Abstract
In the Propp-based story generation mechanisms and the integrated narrative generation system which we havebeen developing, the former functions is a module in the latter. These systems have used respective event
generation mechanisms to generated events which are the most important units in a narrative structuralrepresentation. A common event generation mechanism needs to be used in these two systems towards the complete
blending. This paper will present the first tentative attempt as a prototype to be revised in the future.
Keywords: Narrative generation; Story generation; Integrated narrative generation system; Propp-based story
generation mechanism; Event generation mechanism.

1. Introduction
One of the current major goals in our study is developing
an integrated narrative generation system based on
artificial intelligence, cognitive science and literary
theories. The system aims to organically combine avariety of mechanisms or modules grounded on ourprevious fundamental and individual research results into
one organic mechanism. We have described its ultimate
philosophy and overall design1, and introduced thecurrent status of its actual implementation2. A significant
characteristic of this system’s research is the point that it
adopts an interdisciplinary principle with such literary
theories and narratology as Genette3, Jauss3 and intertextuality. Propp’s theory on “morphology of thefolktales” 4 to be described in this paper is also equal toone of the literary theories relevant to some significant
functions for the narrative generation. We have been
considering the following two types of approaches for theliterary theory by Propp: the first is developing a story
generation mechanism using Propp’s theory ascomprehensively as possible (“Propp-based story

generation mechanism”) and the second approach is its
introduction as one of the modules into the integrated
narrative generation system5.
As described above, the Propp-based story generation
mechanism can function independently to generate stories
with mainly the structural style of a Russian fairy talewhich is the material of Propp’s theory. On the other hand,
we have been addressing the issue of its use as one
module of the integrated narrative generation system6.
For example, we have introduced the Propp-based
mechanism into the integrated system as a set oftechniques to generate macro structures of stories, anddefined a story content grammar relating to theconceptual dictionaries based on our original
interpretation and formalization of an essential part ofPropp’s theory. The event generation mechanism in the
Propp-based mechanism, however, has not beenconnected fully organically to the integrated narrative
generation system. An event means one of the mostfundamental elements in each of the narrative structures
to be generated by the Propp-based mechanism and theintegrated narrative generation system.

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Shohei Imabuchi and Takashi Ogata

The event description forms in the two systems arebasically same, but mechanisms for the respective event
generation mechanisms are not unified formally since thePropp-based event generation mechanism has somespecial techniques to generate stories with the style of a
Russian folk tales and is comparatively simplified. The
Propp-based event generation mechanism, for example,
has a function to set seven types of characters including
hero, villain, victim, helper, dispatcher, donor and false
hero in the Russian fairy tales into an agent in an event,while the event generation mechanism in the integrated
system does not have the function. This paper considers
the two event generation mechanisms in detail tosynthesize them.
Gervás7 describes that many of story generation
systems using Propp’s theory aim at general story
generation mechanisms beyond the description of Proppeven though the most important and essential part in story
generation study using Propp’s theory should be
conducted on the basis of the valuable insight inaccordance with the corpus of Propp. We have also been
insisting that most of the systems using Propp’ theory
focus on only the element of the “function” to bementioned below, but the theory includes many
productive and theoretical ideas to contribute to story
generation in various sides. One of our goals of thePropp-based
story
generation
mechanismisimplementing a story generation system introducing avariety of elements of Propp’s theory as comprehensively
as possible, while another goal is integrating this special
approach into the framework of a more generalizedarchitecture of the integrated narrative generation system.
We simultaneously pursue specialty and generality.
2. An Overview of the Integrated Narrative
Generation System
The integrated narrative generation system consists of thefollowing three types of generation phases: story,
discourse and expression. The system architecture, on theother hand, has the following parts from the type ofprocessing: narrative techniques, knowledge bases, andconceptual dictionaries. For the conceptual dictionaries8,
we have been developing systems for verb concepts,
noun concepts, adjective concepts and adjective verb
concepts with the respective hierarchical structures fromhigher concepts to lower concepts according to a “is-a”
relation. We differentiate a word’s meaning or conceptfrom the word itself as the fundamental policy ofdeveloping the conceptual dictionaries. In particular, one
or more meanings related to a noun are described in thenoun conceptual dictionaries as one or more noun
concepts, and the word to be used normally and thenotations for these concepts are described in anotherlinguistic dictionary. The noun conceptual dictionary
contains 115765 terminal concepts and 5808 intermediateconcepts in the current version. The verb conceptual
dictionary similarly has 12174 terminal concepts and 36
intermediate concepts. A terminal verb concept in thehierarchical structure has the following information: abasic sentence pattern for natural language generation,
one or more case structures and constraints for each of
the cases. A case structure defines several cases for nouns
required in the verb. In addition, knowledge for managing
relations among events and mutual relationships between
events & states are composed on the basis of theconceptual dictionaries for verb and noun concepts. The
input information by a user to the first story generation
phase is several parameters including length, unreality
and repetition. The system selects one or more adequate
story techniques according to the parameters in order toexpand a story tree structure.
Although the Propp-based story generation
mechanism can be used as an independent story
generation system, its integration into the story generation
phase in the integrated narrative generation system
contributes to increase the diversity and flexibility instory generation. A story is described, in the story
generation phase, as a conceptual representation form
including a temporal sequence of events at the bottom
level in a hierarchical tree structure with several types ofrelations as the intermediate nodes. Each of the events is
described as a specific case structure which has a verb
concept and the necessary instantiated noun concepts
linked to the conceptual dictionaries. Fig. 1 shows a story
structure and a case structure of an event within the story
structure. The story generation mechanism generates
story structures having a sequence of events according tostructural operation techniques using the dictionaries andthe other narrative knowledge. We call a procedure for
expanding the tree structure of a story using the story
knowledge base, which stores concrete narrativefragments or structures corresponded to the material for
narrative generation for such various types of narrative
relations as scripts and causal relations, a narrativetechnique for story generation or directly a story

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Integrating the Event Generation

technique. The input to a story technique is an event, thewhole of a story structure or a sub-structure in a story
structure and the output is chiefly the expanded story
structure that is one of the possible various structures.
They can treat from micro story structures to macro ones.
(event Steal(type action)(ID 1)(time (time1 time2))(agent age%Man#1)(counter-agent nil)(location loc%Forest#1)(object obj%Apple#1)(instrument nil)(from age%Boy#1)(to nil))

Conceptual representation of an event“age%Man#1 steals obj%Apple#1 from
age%Boy#1 at loc%Forest#1.”

Relation

E1(t1→t2)

t1

Event

E2
(t2→t3)

t2

t3

State

E3
(t3→t4)t4Conceptual structure of a story

Fig. 1. Structures of a story and an event

3. Propp-based Story Generation System
3.1. The overview
Propp’s theory proposed the concept of a “function”,
which means an action seen from the result and theprinciple of the sequential arrangement of thirty one“functions” as the most important theoretical idea. The“function” of “villainy”, for example, means that acharacter causes the damage of a different character
through a concrete action. However, there is a variety of
specific actions to actualize it since the “function” meansa collective definition to abstractly define many concrete
and real actions. We call more specified actions for
actualizing each of the “functions” “sub-functions” on thebasic of hierarchical concept. Propp described a variety ofexamples corresponded to the level of sub-functions. The“Propp-based story content grammar” based on theframework of Propp’s theory with “functions” and subfunctions is the central part in our Propp-based story
generation mechanism.
We describe the Propp-based story generation
mechanism. A story as the output information isequivalent to a sequence of events bound hierarchicallyusing “story relations” including “causal relation”,“continuation relation”, etc. The form of an event as oneof the basic components in a story takes a frame
representation, which is formed by a verb concept and thecorresponding case elements for such noun concepts asagent, object and location. The verb concepts and noun
concepts are associated with each of the corresponding

elements in the conceptual dictionaries. The structure
generation mechanism and the event concept generation
mechanism are respectively corresponded to generative
mechanisms, while the Propp-based story content
grammar and the conceptual dictionaries are equivalent to
the knowledge parts to be referred by the generative
mechanisms. Since these generative parts and the parts tobe referred by them are mutually independent, theredundancy of processing lessens.
3.2. Propp-based Story Content Grammar
The story content grammar5, 6 that is a new style of thereorganization of Propp’s theory, which gradually
generates a macro story with the structure of the style of a
Russian fairy tale from the highest level to the lowest
level, consists of the following five hierarchical levels.
The actual description by Common Lisp is shown in Fig.
2. The elements including “reserve portion”, “beginning”,
etc. in the level 1 and 2 are defined based on thedescription of structures of Russian fairy tales in Propp4.
The levels of “functions” and sub-functions were
faithfully defined from the description of the analysis of
100 tales. The role of these hierarchical levels is to makethe structural part of a story which is a tree structure withrelations as the intermediate nodes. Events in the level 5,on the other hand, are generated by the event generation
mechanism associating with the above structure
generation mechanism. An event particularly forms acase structure including a verb concept and thecorresponding noun concepts as noted above. We havedefined by hand patterns of these case structures based on
examples corresponded to sub-functions in Propp4. For
example, we have formally defined a case structure of“(interdict 1 (agent human) (object outgo@out)(to !hero))” based on an example in the sub-functions
under “interdiction (γl)” as “If Baba Jaga comes, don’t
you say anything, and be silent.” There is a asset of “Pairof sub-functions” as another significant elements. Thiswas defined according to the description on mutual
relations between two sub-functions in Propp’s theory.

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Shohei Imabuchi and Takashi Ogata(setq *Propp-level1-list*‘ ((Russian folktale(00_Preliminary-part P-Problem P-Trial P-Solution))))(setq *Propp-level2-list*‘ ((P-Problem (Reserve-portion Beginning))(P-Trial (OR (Reserve-trial Battle-and-victory)(Reserve-trial Task-and-solution))) …))(setq *Propp-level3-list*‘ ((Reserve-portion (OR (01_Absentation 02_Interdiction
03_Violation) …))(setq *Propp-level4-list*‘ ((01_Absentation (OR bet-1_Going-out1 bet-2_Deathbet-3_Going-out2))(02_Interdiction (OR gam-1_Interdiction
gam-2_Command-or-proposal)) …))(setq *Propp-level5-list*‘ ((alp-1_Preliminary-part ((Preliminary-part (1))))(bet-1_Going-out1 ((Go-out (agent Parents)(object Business))))(bet-2_Death ((Dead (agent Parents)))) …))

Fig. 2. A part of the description of the Propp-based story
content grammar

4.

Combining the Event Generation Mechanismwith the Integrated Narrative Generation
System

In the Propp-based story generation mechanism, when the
structure generation mechanism reaches to the lowest
level in the story content grammar, the event generation
mechanism is executed to make the event structure basedon the format of the case structure described in the story
content grammar. On the other hand, in a story generation
mechanism in the integrated narrative generation system,
when a story technique refers to the corresponding unit in
the story content knowledge base, the generation
mechanism is executed to make the event structure basedon the format of the case structure described in the story
content knowledge base. The story knowledge base in the
integrated narrative generation system stores concreteknowledge for story generation, in particular a variety ofsequences of events described in the form of casestructure corresponded to the types of relations such as“cause-effect” and “script”. The story content grammar in
the Propp-based story generation mechanism will be alsoa part of the story knowledge base in the future. Twotypes of event generation mechanism have been
independently prepared for the Propp-based mechanism
and the integrated system since both of the description
forms are different each other. To develop a common
event generation mechanism is the goal for incorporating
the Propp-based mechanism into the integrated systemcompletely. We will describe previous four types ofprocedures according to the different types of casestructure’s description in the Propp-based mechanism andthe tentative revision in the integrated narrative
generation system.
When the generation of a story structure according to
the story content grammar in the Propp-based story
generation mechanism reaches to the level of event
generation, the event generation mechanism is executed
to make the case structure. The mechanism inserts
specified instances into each of the cases based on the
difference of the second term in each element of the casestructure. Fig.3 shows an original case structure and atransformed instance by the following techniques in theevent generation mechanism.
Case structure(tell(agent demon_and_ghost)(counter-agent !hero)(object “event 1”)(location !loc1))

Generated event(event tell(agent age%vampire#1) (2)(counter-agent age%Ivan#1) (1)(object (event soak(agent age%Ivan#1) (3)(object obj%steam_bath#1”)))(location loc%house#1)) (4)Insertion of an instance or an event

Fig. 3. The correspondence between a case structure and theactgually generated event(1) When one of the seven types of roles of actors is
described in the second term of a case such as “!hero”,
the event generation mechanism sets the instance of theactor, we call “agent” in the system, based on thepredefined or inputted correspondence knowledge suchas “Ivan: hero”, “Baba-Yaga: donar”, etc. For
incorporating it into the integrated narrative generation
system, when an agent as a Propp-based agent including
hero, heroin etc. appears in a story generation process, thesystem describes the label such as “hero” in the attribute
frame. An attribute frame is a data set associated with anoun concept and the noun concept is embodied byinserting instances or the other various labels into it.
(2) When the value of a case in an event is a name ofa noun concept in which a specified instance of an agent,
an object or a location should be inserted, the event
generation mechanism sets an instance made from a noun
concept in the noun conceptual dictionary selected within
the range of the constraint. The name of the noun concept
specifies the constraint in the current design. For example,
if the name is “demon_and_ghost”, the values to beinserted is selected in the range under the name in thenoun conceptual dictionary. On the other hand, when thename is described in the style such as “horse@beast”, itwill be used as the value directly.

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Integrating the Event Generation(3) When an event concept itself should be the valueof a case (object case in particular) in an event recursively,
the event generation mechanism expands the description
such as “event 1” to a case structure different from thecase structure in which the expanded event is included.
The previous mechanism has used predefined sets of casestructures to be inserted in the position based on
examples described by Propp’s theory. The examples
have not three or more nests. The integrated narrative
generation system uses a recursive function for dealing
with this type of processing based on a predefined list ofnested events. To achieve more general recursive
processing will be a future issue.
(4) When one or more events have a mutualdependence relation, the mechanism processes a special
operation. In particular, when the value of the agent,
object or location in a case structure must be equal to thevalue of the other case structure for the consistency
among events, the mechanism uses a same value for theone or more elements and designates the range which thevalues can take in the noun conceptual dictionary. This isrelated to the “pairs of sub-functions”. The integrated
narrative generation system prepares a procedure for treat
this processing with reference to the story knowledge
base in section II. Each of many data stored in the story
knowledge base is a set with two or more events and theelements in the events need to have a mutual-dependence
relation. One of the issues is that the number in the
Propp-based mechanism is not many, while the numberin the story knowledge base will be very many.

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5. Conclusion
This paper described both of the overviews of our Proppbased story generation system and an integrated narrative
generation system, and presented ways for incorporating
the Propp-based system in the level of event generation
mechanism into the integrated system towards thecomplete blending. The basic policy was that weincorporate the special mechanisms in the Propp-based
system into more generalized mechanisms in the
integrated system, however a part of the mechanisms
such as actors’ roles in the Propp-based system will beconsidered to be arranged in the integrated system too.
References
1. T. Ogata and A. Kanai (2010), An Introduction to
Informatics of Narratology (in Japanese). Gakubunsha.

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