Interactive Storytelling - lecture slides 2012

Interactive Storytelling

© 2008–2012 Jouni Smed

Jouni Smed
jouni.smed@utu.ﬁ
http://www.iki.ﬁ/smed

Course syllabus
• objective:

• credits: 5 cp.


‣ to present the key concepts behind interactive
storytelling
‣ to review the proposed and existing interactive
storytelling systems

Lectures
• lecture times

‣ Tuesdays 10–12 a.m., lecture room λ (C1027)
‣ Wednesdays 10–12 a.m., lecture room β (B1032)
‣ no lectures: November 6, November 7,
November 27, November 28


• October 30 – December 5, 2012

Assessment
• assessment is based on both
‣ writing an essay and
‣ taking an examination


• you cannot pass the course without both!

Examinations
• electronic examination

‣ opens December 10, 2012
‣ closes March 31, 2013

• you can take the examination at most three
• for instructions and examination time
reservations, see https://tenttis.utu.ﬁ/


(3) times

Essay
• an essay of 10–15 pages on a chosen topic
(in English or in Finnish)

‣ topics and material are available in the course’s
moodle page
‣ the essay has to follow the given style standard
‣ deadline: December 13, 2012 (Thursday) 2 p.m.
‣ papers returned after the deadline will not be
graded!


• the essay is returned as a PDF ﬁle

Essay (cont’d)
• grades and possible teacher’s comments
are announced privately through the
course’s moodle page

• all returned essays will be published in the
‣ grades or teacher’s comments are not made
public


course’s moodle page in December 2012

Quick walkthrough

3. Return the PDF version of the essay before
December 13, 2012, 2 p.m. using the essay
return page.
4. Check your essay grade in the course’s
moodle page.
5. Schedule and take an electronic examination.


1. Pick topics that interest you from the list of
topics.
2. Write the essay.

Grading
• grading is based on 20 points

‣ the examination gives at maximum 10 points
‣ the essay gives at maximum 10 points

• to pass the course you need more than 10
‣ you cannot pass the course without both taking
the examination and writing an essay!


points

Grading (cont’d)
• ﬁnal grade:

grade: 1

‣ points: (12, 14]

grade: 2

‣ points: (14, 16]

grade: 3

‣ points: (16, 18]

grade: 4

‣ points: (18, 20]

grade: 5


‣ points: (10, 12]

Course homepage


http://bit.ly/intstory2012

Contents
1. Introduction to interactive storytelling
2. Analysis of storytelling
3. Strategies for interactive storytelling
4. Characters
5. End-user
7. Systems
8. Discussion and conclusion


6. Author


Introduction to
interactive storytelling

Interaction
• “Reciprocal action; action or inﬂuence of

persons or things on each other.” (Oxford
English Dictionary)
active agents in which each agent
alternately listens, thinks and
speaks” (Crawford, 2005)


• “a cyclic process between two or more

Storytelling is about…
• the reasons for actions (not actions)
• people


(Spierling, 2002)

Linear psychological
narrative
• psychological buy-in by the audience
• willing suspension of disbelief


(Perlin, 2005)

Typical features of
storytelling
• contingency: story time/space vs. real time/
space

• narrative representation: the way of
presentation

generation process

(Aylett & Louchart, 2003)


• presence: viewer sharing story time/space
• interactivity: participation in story

Comparison of different
narrative forms
Cinema

Theatre

Literature

Virtual reality

Contingency

low

medium

low

strong

Narrative
representation

visual

visual

mental

visual

not physical

physical

Interactivity

no

no/yes

no

yes


Presence

not physical
not physical
but immersive

Models of user
engagement
•

actual roles that users play in relation to the
narrative experience (Aylett & Louchart, 2007)
Examples

none

conventional audience

non-participant control

conventional authoring; ﬁlm

non-participant inﬂuence

Forum Theatre; The Sims

participant control points

branching narrative

freely participating characters

LARP, emergent narrative


Degree of interactivity

Examples of interactive
storytelling
• inventing and telling a story to an audience
(e.g. children)

• (live action) role-playing games
• improvisational theatre (e.g. Forum
• tour guiding
• teaching


Theatre)

Interactive digital
storytelling
• interactive digital storytelling application is


“designed for users (interactors) to take
part in a concrete interactive experience,
structured as a story represented in a
computer” (Peinado & Gervás, 2007)

Three partakers
Author

Interactive
storytelling
system

End-user

Characters

Forms of interactive
entertainment
computer games
interactive ﬁction
hypertext ﬁction
digital storytelling
scriptwriting software
role-playing games (RPGs)
simulators
narrative intelligence

(Crawford, 2005)


•
•
•
•
•
•
•
•

Uses for interactive
storytelling systems
• art
• entertainment

‣ computer games

• education
‣ children

‣ information kiosks
‣ tour guides


• guidance

Narrative thinking
• fundamental structuring of the human
experience

• autobiographical memory holds stories
about the self



Narrative immersion
• spatial: a sense of place and pleasure taken
in exploring the story-world

• temporal: a desire to know what will

happen next (curiosity, surprise, suspense)

• emotional: affective reactions to the story

(Ryan, 2008)


and to the characters

Conventional narrative
constructed story

presented story

spectator

experienced story

author

Interactive narrative
user

experienced story

characters

external events
author


generated story

Narrative loop
EVENTS

cause

Affective
changes

World
state
changes

cause

cause
ACTIONS

(Aylett et al., 2011)


cause

Degree of interactivity
1. speed
‣ fast turnaround

2. depth
‣ human-likeness
‣ functional signiﬁcance
‣ perceived completeness

(Crawford, 2005)


3. choice

How to interact with
stories?
1. what would change?
2. what would stay the same?
3. how do we make such a thing?

(Perlin, 2005)


4. where is the artist/author located wrt. the
observer/reader

Problems for interactive
drama
1. temporal management of actions:
interesting narrative from the choices?
2. multimodal representation of character’s
actions in a real-time 3D environment
4. authorability: artists should be able to
express themselves
(Szilas et al., 2007)


3. interpreting player’s actions

Challenges for story
generation
1. themes
‣ betrayal, yearning, love, revenge etc.

2. story control
‣ the story must remain dramatically compelling

3. strong, autonomous characters
‣ characters’ reasonable reactions and beliefs

(Bringsjord, 2001)


4. personalization

R&D challenges
1. agency
‣ primary feature offered to the players
‣ player has to be able to affect the plot directly

2. generation

3. interface
‣ expressive, multi-modal interface


‣ real-time generation of content
‣ building blocks

R&D challenges (cont’d)
4. connecting generation and interface
‣ planning and drama management

5. terminology

(Stern, 2008)


‣ young ﬁeld still lacks proper terms
‣ e.g., ‘storytelling’ or ‘storymaking’

Narrative paradox
• “pre-authored plot structure conﬂicts with
the freedom of action and interaction
characteristics of the medium of real-time
interactive graphical environment”




Analysis of storytelling

Sources
• Aristotle: Poetics (ca.
• Vladimir Propp:

• A.J. Greimas
• Roland Barthes
• Claude Bremond
• Brenda Laurel:

• Joseph Campbell: The

• Janet Murray: Hamlet

• Russian formalism
(1916–1930s)

Morphology of the
Folktale (1928)
Hero with a Thousand
Faces (1949)

Computers as Theatre
(1991)
on the Holodeck
(1997)


335 BCE)

Aristotle: Poetics

Thought
Language
Pattern
Enactment


Material cause

Character

Inferred formal cause

Action

Aristotle: Narrative forms
‣ events represented
through verbal
narration (diegesis)
‣ focus on the exploits
of a solitary hero
‣ story can be endlessly
expanded
‣ motivations of the
hero remain fairly
simple

• dramatic
‣ events represented
through the imitation
of action (mimesis)
‣ focus on the evolving
networks of human
relations
‣ action is mental rather
than physical
‣ the dramatic arc


• epic

a) exposition
b) inciting incident
c) rising action
d) crisis
e) climax
f) falling action
g) dénouement

complication

e
d
c
a

b

f

g
time


The dramatic arc

Third narrative form:
Epistemic narrative
• emerged in the 19th century
• superposition of two stories

‣ events that took place in the past
‣ an investigation that leads to their discovery

• driven by the desire to know (e.g. mystery
(Ryan, 2008)


story)

Interactivity and narrative
forms
‣ accomplishement of a
mission
‣ used in many games

• epistemic

‣ player as a detective
‣ author-defined story –
variable story
‣ elucidation of the
mystery until the
solution is found

• dramatic

‣ most difficult to
implement
‣ goals of characters
evolve together with
their relations
‣ requires constant
redefinition
‣ simulation of human
reasoning

(Ryan, 2008)


• epic

Russian formalism:
Model of narrative
1. Fabula
‣ logically and chronologically related series of events
caused/experienced by the characters in the
storyworld

2. Sjužet

3. Media/text
‣ the surface of the story expressed in language signs


‣ the ﬁnished arrangement (i.e. the plot, сюжет) of the
narrated events as they are presented to the reader

Vladimir Propp:
Morphology of the Folktale

‣ “act of a character deﬁned from the point-ofview of its signiﬁcance for the course of action”
‣ independent from the character who performs it


• analysis of Russian folktales
• 31 narrative units (i.e. narratemes)
• character function

Narratemes and spheres
• introduction
‣ βγδεζηθ

• the body of the story
‣ ABC↑

• the donor sequence
• the hero’s return

‣ ↓PrRsoLMNQExTUW


‣ DEFGHJIK

α – initial situation

↑ – departure

↓ – return

β – absentation

D – the first function
of the donor

Pr – pursuit, chase

E – hero’s reaction

o – unrecognized
arrival

δ – violation
ε – reconnaissance
ζ – delivery
η – trickery
θ – complicity
A – villainy

F – provision or
receipt of a magical
agent
G – spatial
transference between
two kingdoms,
guidance

B – mediation, the
connective incident

H – struggle

C – beginning
counteraction

I – victory

J – branding, marking
K – resolution

Rs – rescue

L – unfounded claims
M – difficult task
N – solution
Q – recognition
Ex – exposure
T – transfiguration
U – punishment
W – wedding


γ – interdiction

Example sequences
‣ δηθ – the villain succeeds in deceiving the victim
‣ DE – the hero is tested to get a magical agent
‣ HJ – the hero ﬁghts and gets injured

‣ ↓oLQEx – the hero returns but a false hero has
taken his place; the hero is recognized and the
false hero is exposed


‣ ↓oMNQ – the hero returns but is not
recognized until he passes a test

Example tale
• A tsar, three daughters (α). The daughters

• αβδABC↑H-IK↓W


go walking (β), overstay in the garden (δ). A
dragon kidnaps them (A). A call for aid (B).
Quest of three heroes (C↑). Three battles
with the dragon (H-I), rescue of the
maidens (K). Return (↓), reward (W)

• Villain
• Donor
• Helper
• Princess (and her father)
• Dispatcher
• Hero
• False hero


Character roles

Moves
• list of functions that make a subsection of

‣ one move follows directly another
‣ new move begins before the end of old move
‣ second move is interrupted by a third move
‣ two villainies occur at once
‣ two moves have a common ending
‣ two protagonists part at a road marker with an
exchange of signalling objects


the story (usually ending on F, K, Rs or W)

Joseph Campbell: The Hero
with a Thousand Faces
• monomyth (i.e. the hero’s journey)

‣ common pattern with strong reference symbols

• symbolic representation of the passage
‣ departure
‣ initiation
‣ return


from childhood to adulthood

Separation

Innocent world
of childhood

Freedom to live
Master of two worlds
Rescue

Call to adventure

Magic flight

Refusal of call

Refusal of return

Supernatural aid
Crossing the
first threshold
Belly of the whale

The Hero’s
Journey

Return
The ultimate boon

Apotheosis

Road of trials
Tests and ordeals
Dragon battle

Nadir
Crucifixion
Symbolic death/dismemberment
Sparagmos

Meeting with
the Goddess

Atonement to
recognition by
Father

Initiation

A.J. Greimas: Actant model
• first role-based analysis of narrative

‣ background: semantics and structuralist stance

• formalization of Propp’s roles

‣ not for what they are but for what they do

• the actant model can be instantiated by a
(Cavazza & Pizzi, 2006)


specific semantic field

Generic actant model
Object

Sought-for person

Helper

Subject

Antagonist

Dispatcher

Roland Barthes:
Interpretative codes
• ACT (action)

‣ generalization of narrative function
‣ action sequences
‣ background knowledge required for
interpretation
‣ contextual knowledge


• REF (reference)

Interpretative codes
(cont’d)
• SYM (symbolic)

‣ major cultural objects that symbolic (e.g., money)

• SEM (semantic)

‣ choice of words to narrative events
‣ items that should trigger interpretation
‣ cues for future events
‣ elements of mystery relevant to the story


• HER (hermeneutic)

Claude Bremond: Agent
and patient
• agent is responsible for the changes in the
narrative universe

‣ voluntary or unintended
‣ types: inﬂuencer, improver, protector, frustrator

• patient is inﬂuenced by the narrative actions
• transient status: characters can alternate
between the roles


‣ awareness of the situation
‣ the situation itself

Brenda Laurel:
Computers as Theatre
• “When we look toward what is known

about the nature of interaction, why not
turn to those who manage it best – to
those from the world of drama, of the
stage, of the theatre?” (Laurel, 1991)
‣ designing an interface is the real problem
‣ creating a representational world that leaves the
feeling of the interface behind


• invisibility of the computer

Material for action

Material cause

Thought
Language
Pattern
Enactment

User interaction

Character

Inferred formal cause

Action


Neo-Aristotelian theory
of interactive drama

The ﬂying wedge of
possibilities
Potential
Probable
Potential
t


Possible

Necessary

Janet Murray: Hamlet on the
Holodeck
• can a computer provide the basis for an
expressive narrative form?

• Star Trek’s holodeck as an ideal model of

interactive narrative

Representational strategies

(Murray, 1997)

• navigable space
• encyclopedic capacity
• participation
• procedurality

Phenomenal categories

(Murray, 1997)

• immersion
• agency
• transformation

Lessons from the
holodeck: goals to pursue

(Ryan, 2008)


• natural interface
• integration of user actions within the story
• frequent interaction
• dynamic creation of the story
• ability to create narrative immersion

Mapping and recapping the
theoretical background 1(4)
Aristotle’s Poetics
Laurel: Computers as Theatre

Mateas & Stern: Façade
(Koenitz, 2010)


Carnagie Mellon: OZ project

Derrida, Foucault, Barthes, Eco, Baudilard
Storyspace platform

Joyce: Afternoon
Jackson: Patchwork Girl

(Koenitz, 2010)


hyperﬁction

non-literary, non-western tradition
(e.g., oral narratives)

(Koenitz, 2010)


Jennings: the book of ruins and desire
Harrell: Griot system

Barthes, Bremond, Prince, Genette, Chapman
narratology

(Koenitz, 2010)


interactive ﬁction (IF)


Strategies for

Strategies
• author-centric

‣ explicit authoring

• character-centric


‣ emergent narrative
‣ implicit creation

Measures
• plot coherence

‣ the perception that the main events of a story
are causally relevant to the outcome of the story

• character believability

(Riedl, 2004)


‣ the perception that the events of a story are
reasonably motivated by the beliefs, desires, and
goals of the characters

Author-centric
• models the creative process of a human
author

• explicit authoring: predeﬁned template to
• strong plot coherence
• not so strong character believability


follow runtime

Example: The Oz Project’s
Interactive Drama Engine
Presentation

Drama manager

World
Character
Character


Player

Character

Drama manager
techniques
• branching narrative
• universal plan

‣ beats (i.e. action–reaction pairs)
‣ interactive plan trees (e.g. HTN)
‣ anticipation of every possible action
‣ combinatorial explosion

(Louchart & Aylett, 2005)


• problems

Drama managers ways to
inﬂuence

(Crawford, 2005)


• environmental manipulation
• goal injection
• shifting personality
• ticking clock of doom
• dropping the fourth wall

Character-centric strategy
• autonomous characters: models the mental
factors that affect how characters act

• the story emerges from the characters’
decisions and interaction

• implicit creation: narrative planted
• strong character believability
• not so strong plot coherence


beforehand

Emergent narrative
• term introduced by Aylett (1999)
• story emerges bottom up based on

characters described top down by the
author

• exhibits perpetual novelty

Example: Reality TV
• emergent narrative as a source for a story
• participant
‣ motivated by money, fame etc.
‣ subjected to entertain the spectators
‣ gets entertainment
‣ lacks inﬂuence on the narrative


• spectator

Example: Reality TV
(cont’d)
• programme production team
‣ pre-production selections

- choice and deﬁnition of the main protagonists
- designing the world environment to foster emotions
‣ performance time control



- tasks, eliminations etc.
- compiling a broadcast to the spectators

Storyworld
recepient

designer

Narrative interpretation

Emergent system

storyworld = mental model

storyworld = model, rules

world state → mental state

world state → world state

states, actions, events

generating from
the rules
states, actions, events


reconstruct storyworld
by inference

(Spierling, 2007)

Gardening metaphor
• author-centric

‣ explicit authoring is like creating a paper ﬂower

• character-centric

‣ implicit creation is like planting a ﬂower

(Spierling, 2007)


Characters

Features of believable
agents
• personality

‣ unique and speciﬁc, not general

• emotion

‣ exhibit and respond personally-speciﬁcally

• self-motivation
• change

‣ growth and change with time (wrt. personality)


‣ internal drives and desires

Features of believable
agents (cont’d)
• social relationship

‣ interaction with others changes the relationships

• illusion of life

(Mateas, 2002)


‣ multiple goals
‣ broad capabilities
‣ quick reactions

Character behaviour
1. low level (e.g. collision detection)
2. social interaction (e.g. introducing oneself)
3. idle behaviour
4. targeted behaviour (i.e. go for the goal!)

(Fairclough & Cunningham, 2002)

Expressiveness
• independent from visual realism
• origins of expressive behaviour:
‣ agent itself
‣ human creator


(Szilas, 2007)

Flashback: Crawford on
interaction…
• “a cyclic process between two or more

active agents in which each agent
alternately listens, thinks and speaks”

Character’s interaction
• listen

‣ perception of the world

• think

• speak

‣ acting in the world


‣ coloured by the character’s personality
‣ associated with and stored to the character’s
memory

The perception system in
VIBES
1. acquisition sensors: abstract description of
the world
2. perception ﬁlters: simulation of the physical
sensors

(Sanchez et al., 2004)


3. cognitive ﬁlters: support for the decisionmaking

Crawford’s personality
model 1(2)
Accordance

Relationship

Integrity

“gullibility”

“trust”

Virtue

“willingness to see
good”

“virtue perceived”

Power

“timidity”

“fear of power”

Intelligence

“judging others wise”

“respect”

“vanity”

“attractiveness
perceived”

Attractiveness


Intrinsic

Crawford’s personality
model 2(2)
Volatility

Anger/Fear

Adrenaline

Joy/Sadness

Manic/Depressive

Arousal/Disgust

Sensuality
(Crawford, 2005)


Mood

Event-appraisal theory
• OCC-model (Ortony, Clore and Collins)
• emotional state
‣ positive/negative
‣ intensity

objects varies according to their emotional
state
(Theune et al., 2004)


• agents reaction to events, actions and

OCC-model
Directed to other agents

hope – fear

admiration – reproach

joy – distress

hope – fear

pride – shame

love – hate


Directed to agent itself

Autobiographical memory
types
• type 0: agent is always telling the same
story

• type I: agent has a variety of stories but not
within the conversational context
context best


• type II: agent selects a story that ﬁts the

Autobiographical memory
types (cont’d)
• type III: agent tells and listens stories (i.e.

interprets the meaning and has a response)

• type IV: a living, autonomous agent (i.e.
personality)


(Ibanez et al., 2003)

Memory in VIBES
• stores information (i.e. percept objects)
acquired about the world

‣ actor’s representation of the world
‣ knowledge the actor has acquired

• records consecutive internal states of the
(Sanchez et al., 2004)


actor (e.g. wants, emotions)

Memory in SAGA
• narrative memory stores a temporal
sequence of episodes

‣ cause-and-effect links between episodes
‣ crisis
‣ climax
‣ resolution

(Machado et al., 2004)


• episode comprises

Episodic memory
• personal history of an entity
‣ places and moments
‣ subjective feelings and goals

• requires: persistent world and multiple
actors
scope

(Brom et al., 2007)


• autobiographic memory: longer, lifetime

Requirements for a full
episodic memory
1. storing complex hierarchical tasks
2. storing and reconstructing personal
situations


‣ what, with which and why?
‣ who saw and what did he do?

Full episodic memory
(cont’d)
3. all available information is not stored
‣ perceivability
‣ importance
‣ attractiveness (or salience)

5. coherence: trust in the stored data
(Brom et al., 2007)


4. large time scale: the importance of
forgetting (details reduced, events merged)

Late commitment
• character agent’s decisions
‣ in-character (IC)
‣ out-of-character (OOC)

• improvisational theatre: no agreed upon
‣ implicit OOC communication (e.g. “Hello,
daughter.”)

(Swartjes et al., 2008)


storyworld but framing as the actors go
along

Late commitment (cont’d)
• explicit OOC communication
‣ framing operators

• late commitment



‣ goal management: goals from OOC if no other
goals exist
‣ action selection: agents can create OOC plans
for their goals

Late commitment:
observations
• IC actions should not be selected to satisfy
the preconditions of framing operators

• an action contradicting a framing operator
has to be ordered after the framing
operator

• all characters must unconditionally accept


all framing operators

Problem of believability:
The uncanny valley
• Masahiro Mori (1970):

• the uncanny valley: the area of repulsion

between “barely human” and “fully human”


‣ the more human-like the robot, the more
positive the emotional response
‣ at some point the response becomes quickly a
strong repulsion
‣ as the appearance and motion improve,
emotional response becomes positive again

The uncanny valley:
Movement and appearance
healthy
person

response

+

android/
gynoid
industrial
robot

corpse/
zombie

bunraku
puppet

prosthetic
hand

–
0%

human-likeness

100%


End-user

Affordance
• interface design: opportunities for action
made available by an object or interface

• interface “cries out” for the action to be
taken


(Mateas, 2002)

Choice problem
• how to choose from a large amount of
possible actions?


(Szilas, 2004)

Interface mapping function
• P: physically possible
actions

f

L

• L: logically (in the
story) possible
actions

‣ real affordances

P

‣ perceived affordances

Interface mapping function
(cont’d)
• total

‣ non-surjective: ﬁltering
interface
‣ non-injective: redundant
interface
‣ bijective: direct interface
‣ free interface: free
interface


• partial

Anticipation of an action
• author’s activity: plan the user’s inferences
• stability: P and L should remain stable
• surprise: counters stability
‣ new possibility should remain in the selection
‣ addition in slow pace
‣ freeze or ﬁll in the time
‣ semi-autonomy
‣ ellipsis


• duration of interaction

User-centred actions
• ethical consistency
• motivational consistency
• relevance (history)
• cognitive load (opens/closes narrative
processes)
conﬂict)



• conﬂict (exhibits or pushes towards a

Inferring player states
• inferring player’s knowledge
• inferring player’s preferences
• inferring player’s goals


(Thue et al., 2008)

The role of the end-user?
• users probably do not want to be tragic or
comic heroes

• many users do not even want to be actors
but marginally involved observers or
conﬁdantes

(Ryan, 2008)


‣ a peripheral character affecting the world and
observing the outcome (i.e. agent and spectator)

Robin Laws: Seven player
types
1. power gamer: new abilities and equipment
2. butt-kicker: ﬁght!
3. tactician: thinking ahead
4. specialist: sticks with his favourite character

6. storyteller: plot threads
7. casual gamer: in the background


5. method actor: want to test his personal
traits


Author

Author
• authoring = delivering content for
somebody else’s experience

• author deﬁnes

(Spierling, 2009; Spierling & Szilas, 2009)


‣ actions
‣ states
‣ events

A contract with the author
• there is a reason why the author is leading
you through the story

• how does that work in an interactive story?


(Perlin, 2005)

Narrative paradox and
authoring

• the author cannot expect the user to make

the right decision at the right moment or in
the right place

• author’s role is to write interesting

characters and rely on their ability to
interact with one another
user’s inner state



• author must be extremely attentive to the

Second person insight
• the ability to think in terms how the
expression will be perceived by the
audience


(Crawford, 2005)

Authoring challenges
• authored content depends on the run-time
system architecture

• the increase in the amount of content
• not a single author task


(Aylett et al., 2011)

Problems
• ﬁnding IS authors

‣ reluctance to reduce human affairs into logical
models

• abstraction

‣ writing must be at the level of story-related
abstract structures
‣ e.g., XML, Excel

• algorithm-centered story design


• formatted and constrained writing

Problems (cont’d)
• the potential of engines underused

‣ reduction to linear or branching structure
‣ no inspiring examples, lack of prototypes

• authoring and programming intersecting
(Spierling, 2009; Spierling & Szilas, 2009)


‣ storyworld and engine have a blurry line
‣ immaturity of the medium

Boundaries of authoring
end-user

interaction

author

storyworld

IS
artefact

IS
experience

developer

(Spierling & Szilas, 2009)


runtime engine

Principles of design
• main characters

‣ limit the number
‣ give clear relationships to one another within a
dramatic situation

• character deﬁnitions
• parallel characters

‣ draw clear contrasts (e.g., rivals, friends, enemies)


‣ along the spectrum based on the value system
central to the story

Principles of design
(cont’d)
• characters as foils for one another
‣ emphasize similarities and differences

• narrative events

(Murray, 2011)


‣ combine functions of an overarching frame story
‣ create coherent nested sequences

Potential inﬂuence
abstract
storyworld

action selection

action and
behaviour
models
(Spierling, 2009)


staging /
shape of
events
(representation)

narrative discourse / sequence of events

Models of actions, states
and events
1.possibility for action
2.actualization
3.result of the action

• von Wright: logic of

3.state without the
action

• AI planning
1.pre-condition
2.action
3.post-condition

(Spierling, 2009)

action

1.intial state
2.end state after action


•

Bremond:
elementary
sequence

Creative process of the
author
• debugging

‣ altering and adapting the story content to match
the authorial intent

• co-creation

(Swartjes & Theune, 2009)


‣ embracing the possible stories and letting it
change the original authorial intent

Authoring types
• content authoring

‣ which instances of story elements are in the
domain?
‣ which actions, goals etc. may occur?

• process authoring



‣ how do the element connect causally?
‣ when do the elements occur?

Iterative authoring
1. idea generation
‣ get inspired
‣ ﬁnd ﬂaws

‣ feel out the
storyscape
‣ detect surprising
behaviour

2. implementation
‣ add new content
and processes
‣ constrain the
domain


3. simulation

Principles of delayed
authoring

• AI in an IDS system is a decision-making
proxy for the interactive story’s authors

• delay story decisions made online:

maximize the chance of new player
information
authoring process: it is better informed by
inferred player information?
(Thue et al., 2008)


• a story decision arising during the

Authoring in emergent
narrative
• interactive story

‣ who tells?
‣ to whom?
‣ what is the story?

(Louchart et al., 2008)


• sender, receiver, message

Sender and message
• sender

‣ narratorship shared between the system and the
interactor

• message


‣ the interactor can construct their own message

Receiver
• the notion of agency
• not necessary to predict the consequences
of an action

• interactor can make choices they would

• willingness to play within the role and its
constraints


not do in real life (even if they know the
consequences)

Landscape of possible
stories
• point: possible state
• climbing hill: moving towards dramatic
necessity (i.e., ﬂying wedge)

• valley: offers potential mountains



Design suggestions (1)3
• justify the existing boundaries


‣ spatial
‣ contextual
‣ interaction

• critical mass for emergence

‣ density: how well the authored content serves to
create different paths
‣ added content


- new possibilities
- widens the boundaries and reduces density

• dead ends

‣ narrative end = lack of content
‣ continuing process involving ﬁnding dead ends
and resolving by adding new content



Process of authoring
• modelling a dramatic abstraction of reality

‣ how the characters behave (not how people are
behaving in reality)

• modelling implies complexity reduction
‣ too much generalization can lead to
uninteresting stories

plot



• author should not think in the terms of

• Improv: scripts
• Hap/ABL: hierarchy of goals
• FSMs/hierarchical FSMs
• Motion Factory: graphical editors
• Softimage
• Virtools: ﬂow charts
• BEcool: oriented graphs

(Szilas, 2007)


Authoring tools and
methods

What does an author
want?
• testing

‣ debugging
‣ parameter tweaking
‣ replaying

‣ but what is actually the author’s role in
interactive storytelling?


• feedback from the users
• artistic control


Systems

General scheme of an IS
software
1. reasoning (decision-making, planning)
2. behaviour
3. animation (triggered by behaviour)

(Szilas, 2007)

Four-level story engine
1. story engine (ﬂow of the story)
‣ narrative function the next scene should fulﬁl;
gets story acts

2. scene action engine (play scene using a
narrative function)

4. actor avatar engine
(Spierling et al., 2002)


3. character conversation engine (sends stage
directions)

Four-level story engine
(cont’d)
axis: predeﬁned – autonomous
1. strict – dynamically chosen scene
2. predeﬁned scripts – generated scripts
3. dialogue – intelligent agent
4. stored animations – adapted animations

•

• CrossTalk
• Façade
• Interactive Drama Engine
• Makebelieve
• SAGA
• Storytron
• Virtual Storyteller


Reviewed systems

CrossTalk
• interaction triangle: three screens
‣ virtual exhibition hostess
‣ changeable virtual exhibition visitors
‣ touch screen for the user’s choices


(Klesen et al., 2003)

Narrative structure vs.
story content
1. scene ﬂow deﬁnition
2. scene content creation


‣ author’s scripts
‣ automatic dialogue generation

SceneManager
• scene

‣ pieces of user-edited dialogue
‣ coherent and closed unit wrt. message, agent
characterization or punchline

• compound scene = linked atomic scenes
• scene group = set of equivalent atomic
• scene ﬂow: narrative structure linking the
scenes


scenes

SceneManager (cont’d)
• scene node

‣ prescribed
‣ customically created
‣ interrupt
‣ conditional
‣ probabilistic


• scene transition

SceneManager (cont’d)
• user input


‣ request and wait
‣ time-out events
‣ interrupt (seamless interaction)
‣ concurrent event handling (affect long-term
behaviour)

Dialogue strategies: plan
operators


• context: goal and precondition
• dialogue content
• characters: role & personality
• role & meta-role (trick for immersion)

Façade
• story set-up

‣ player takes the role of a close friend of Trip and
Grace, a couple whose relationship is in trouble
‣ events takes place at Trip’s and Grace’s home
where the player is invited to have a cocktail
‣ moving and interacting in a 3D environment
‣ typing in utterances

(Mateas, 2002; Mateas & Stern, 2004)


• player’s control

System structure
• story comprises dozen carefully scripted
interactive narrative scenelets

• time is discretized into beats

‣ the smallest unit of a value change (i.e. an action–
reaction pair)

the relatively linear set pieces


• techniques to steer the narrative towards

Broad-and-shallow
approach
• idea inherited from the Oz project

‣ broad: all necessary features have an
implementation
‣ shallow: some features could have been
performed better

necessary intelligently, in a wide range of
situations


• characters can act believably, but not

Surface-text processing

1. map surface text into discourse acts


2. map discourse acts into character
responses

Discourse acts
negative
exclamation

• express of
emotion

• unsure or
indecisive

• thank
• greet

• ally/oppose
character

• don’t

understand

• apologise
• praise/criticize
• ﬂirt
• pacify
• explain

• advice
• refer to
• ask to share
intimate
thoughts

• say goodbye
• miscellaneous
discourse act

• can’t

understand


• agree/disagree
• positive/

Interactive Drama Engine
• prototype system

‣ non-linear narrative
‣ 3D characters
‣ graphical user-interface


IDE architecture
Narrative engine
Narrative
structure

Action
generation

Action
selection

Behavioural engine

Narrative
GUI

Game engine

Player


Text
generation

Makebelieve
• virtual guide system, which uses
‣ Jess/CLIPS reasoning system
‣ OpenMind common sense data
‣ Unreal Tournament engine


(Ibanez et al., 2003)

Story element
• name
• type of event
• location
• attributes (nature of

• special environment

• basic concepts

• subject: of the fact
• object: of the fact

(deﬁned in
knowledge base)

• date

• granularity: ‘size’
• effects: caused by
this


the element)

condition

Method
1. initial situation; input
2. select a story element
3. add related story elements (causation)
4. translate according to the guide’s attitude
5. consider common sense rules
7. generate storyboard


6. extend story with common sense

SAGA
• no predeﬁned story
• users interacting with autonomous

character collaboratively play the role of
the author

• director: guide the accomplishment of a

(Machado et al., 2004)


meaningful story

SAGA system
• based on Propp’s narrative morphology
• story deﬁnition
‣ initial story situation
‣ variable story schema

goals → plan → hierarchy of goals and
actions


• function → plot point → set of generic

Director agent
1. update situation
2. conﬂict? → select a new episode
3. current plot point achieved? → select the
next plot point
5. new story element introduction needed?


4. reﬂection event needed?

Storytron
• components

‣ authoring tool SWAT
‣ storyworld library

• launched 2006; discontinued 2011
• originally developed under the name
(Crawford, 2005)


Erasmatron

Virtual Storyteller
• multi-agent framework

(Theune et al., 2004;
Swartjes & Theune, 2006)


‣ plot generation
‣ natural language generation
‣ presentation by an embodied agent

Plot generation
• select “episodic script” from a database
‣ setting: location, characters,objects
‣ goals
‣ constraints

before carrying out a plan


• character asks the director’s permission

Plot generation (cont’d)
• within episode characters are free to choose
action


‣ subjected to probabilistic emotions (OCC-model)
‣ example: 90% fear means 0.9 probability of choosing a
cowardly action

General transition model
(GTN)
‣ G – goal
‣ A – action
‣ O – outcome
‣ E – event
‣ P – perception
‣ IE – internal event

• causal relationships

‣ φ – physical
causality
‣ m – motivation
‣ ψ – psychological
causality
‣ e – enablement

• elements

GTN (cont’d)
ψ
IE

φ/e

E

φ

P

ψ

m

G

ψ

m/e
m

A

φ
φ/e

ψ

O

ψ

ψ

Decision-making in

• six general properties of story events

• cf. the six questions in journalism

‣ who? what? when? where? why? how?


‣ idea: what is the occurring action
‣ actors: who or what is acting or being acted upon
‣ time: when does the action occur
‣ place: where does the action occur
‣ actions: what changes
‣ reasons: why does the action occur

(Thue et al., 2008)

Story decisions and design
decisions
story decision

property

design decision

idea

what should happen?

result

what was decided?

actors

who should be involved?

chooser

who made the decision?

time

when should it happen

time

when was the decision made?

place

where should it happen?

—

—

actions

how should it happen?

method

how was the decision made?

reasons

why should the actors act?

justiﬁcation

why was the decision made in
that way?


property

Story decision properties
for Façade
chooser

time

method

justification

idea

author

offline

imagination

no restrictions

actors

author

offline

imagination

no restrictions
follow dramatic
principle / respond to
player

player & author

online & offline

place

author

offline

imagination

no restrictions

actions

player & author

online & offline

interruptible
scripts

allow player
interactions

reasons

author

offline

imagination

no restrictions


time

tension arc /
player interest


Discussion and
conclusion

Adaptation for interactive
stories
media

• adaptation types
‣ scissors adaptation
‣ distilled adaptation
‣ expanded adaptation
‣ straight adaptation
‣ wild adaptation

• adaptation in

interactive
storytelling:
expanded or wild
‣ formalize the story
into an abstract form
‣ make a creative
interpretation and
adaptation
(Spierling & Hoffmann, 2010)


• translation between

Multiuser interactive
storytelling

• multiple users in application means handling
conﬂicts

‣ intervowen stories that consistent, responsive
and compelling
‣ solving the too-many-heroes problem
‣ maintaining persistency
‣ preventing cheating

(Smed, 2011)


• challenges

Too many heroes
• how to guarantee dramatically compelling
story to everyone?

• each human-controlled character needs a

‣ each new brings along extras
‣ limit the number of human-controlled characters


group of computer-controlled characters to
support them

Persistency
• how do we handle players entering and
leaving at any time?

‣ user’s character vanishes from the storyworld
‣ user’s character becomes a computer-controlled
character
‣ user can give tactical level instruction to
character to follow during the absence


• when the user leaves the storyworld

Cheating
• every action within the storyworld should
be valid

• limitations exist

‣ e.g. zombie attack and “I’ve been shot” in Façade
‣ is collusion cheating in an interactive story?


• how about multiple users?

Motivations for rereading
interactive stories 1(3)
• making sense of things

‣ new fragments to be reconciled into the overall
understanding of the story

• ﬁnding out more

• trying out “what-if” scenarios

‣ different choices can lead to different outcomes


‣ there is more to the story than can be seen on
the surface

• seeing things from a different perspective
‣ radical revision of

- player’s model of the storyworld
- character’s personality and motivation
- causal connections

‣ process of looking for an interpretation of the
text


• looking for a deeper meaning

• reﬂecting on the techniques used

‣ appreciating or critiquing the ways in which the
text achieves its effects

• ﬁguring out how the system works

(Mitchell, 2010)


‣ what is the underlying role system

Dramatis Personæ
1986–2002
Brenda Laurel

Michael Mateas
Andrew Stern

Chris Crawford

Janet Murray

Joseph Bates

Dramatis Personæ
2003–
Stefan Göbel
Ruth Aylett
Sandy Louchart

Ulrike Spierling
Nicolas Szilas
Ivo Swartjes

Ana Paiva

Mariët Theune


Marc Cavazza

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