=Paper=
{{Paper
|id=Vol-2282/EXAG_106
|storemode=property
|title=Wonderful Design: Applying Appraisal Theory to Procedural Level Generation
|pdfUrl=https://ceur-ws.org/Vol-2282/EXAG_106.pdf
|volume=Vol-2282
|authors=Rosa Corstjens,Anders Bouwer,Joris Dormans,Riemer van Rozen
|dblpUrl=https://dblp.org/rec/conf/aiide/CorstjensBDR18
}}
==Wonderful Design: Applying Appraisal Theory to Procedural Level Generation==
https://ceur-ws.org/Vol-2282/EXAG_106.pdf
Wonderful Design: Applying Appraisal
Theory to Procedural Level Generation
Rosa Corstjens1 Anders Bouwer1 Joris Dormans2 Riemer van Rozen1,3
1 2 3
Amsterdam University of Applied Sciences Ludomotion Centrum Wiskunde & Informatica
Amsterdam, The Netherlands Amsterdam, The Netherlands Amsterdam, The Netherlands
r.a.s.corstjens@hva.nl a.j.bouwer@hva.nl joris@ludomotion.com r.a.van.rozen@hva.nl
Abstract understood to be the effect of the game as intended by the
Procedural level generation for games is an active field of designer on the player’s experience and affective state. We
research with successful applications. However, how to wish to learn how level designers can set the stage for gram-
generate content that embodies design intent is still an open mar-based procedurally generated game levels, much like a
research question. Level designers lack abstractions and tools director would for theatrical plays.
for authoring generated artifacts for affecting emotion. We
propose a novel pattern language for generative level design This paper assesses the feasibility of formulating a design
inspired by Appraisal Theory. Its patterns enable designers to pattern language for affecting emotions in level design
add meaning, depth, and cohesiveness to the resulting con- and the implementation of those patterns in generative
tent, and modify artifacts to make the content more engaging. grammars for procedural level generation in order to help
We illustrate how these patterns can be implemented in a gen- achieve this type of direction. Our approach is based on
erative grammar for level generation for an adventure game.
Formative evaluation of generated level content demonstrates Appraisal Theory (Smith & Lazarus 1990; Ellsworth &
the feasibility of the approach and suggests points for further Scherer 2003), which explains how emotions arise from
improvements. Future work could focus on other elements appraisals made by people regarding their environment. The
which seem important for affecting emotions, including main research question we address is the following: How
pacing, perception, and expectation. can Appraisal Theory be used to create design patterns for
affecting emotions, and how can these be implemented
Introduction using generative grammars for procedural level generation?
The assumption is that patterns for affecting emotions are
Procedural level generation is a kind of Procedural Content able to make the content more engaging and contribute to a
Generation (PCG) that helps level designers author game more coherent player experience. The research is carried out
levels (Shaker et al. 2016). In this study, we focus on ap- in the context of a commercial adventure game currently in
proaches to PCG that employ generative grammars. Instead development, which relies on advanced content generation.
of creating the levels by hand, designers author grammar The approach presented here is meant to be general enough
rules that transform level artifacts step-by-step, generating a to be applied to level generation for other adventure games,
wide variety of playable environments, missions, quests and in particular methods that incorporate generative grammars.
stories (e.g., see Dormans 2010; Karavolos et al. 2015). Ultimately, the goal is to enable the discipline of level direc-
However, not all generated levels focus the attention and tor who orchestrates the level generation process and affects
gameplay experiences in the way the designer intended, related dramatic aspects for improving the overall perceived
since it is difficult to control the generation of the situated quality and player experience.
content, e.g., in setting the stage for encounters and flow in
landscapes that fit a story as it emerges. Moreover, abstrac-
tions and tools for designing and improving generated levels Related Work
that evoke emotional responses are currently missing. As a
Generating content that embodies game design intent is a
result, generated levels are not guaranteed to represent the
key open research challenge. Here we relate our work to
design intent, and regularly also contain noisy, distracting
conceptual frameworks, techniques for PCG, design pattern
peculiarities that can break immersion. Design intent is
languages, and emotional modeling.
Proceduralist readings is a framework that connects game Design patterns
elements, mechanisms and dynamics, and explicitly formu- Design patterns were first introduced by architect Alexander
lates rhetorial arguments in a thematic and cultural setting et al. (1977) as a formal description of a problem-solution
from which meaning is derived (Treanor et al. 2011). We pair. Since then, many design pattern languages arose, ad-
model gameplay assumptions explicitly too, but instead fo- dressing different problems. Björk and Holopainen (2004)
cus on emotional effects as guided likely outcomes of an ap- define a catalogue of abstract gameplay interaction patterns
praisal of interacting with generated content. that describe how components are used by a player to affect
the gameplay outcome. Zagal et al. (2007) take an onto-
Procedural Level Generation logical approach that describes and relates hierarchies of
Procedural content generation can be employed for various concepts and intents to weak and strong examples. These
reasons, including generating variations for increased re- descriptive approaches are suitable for analyzing, critiquing
playability, saving time for the designer by automating the and understanding games, but they do not prescribe how to
design process, gaining a better understanding of the crea- modify and engineer a game prototype.
tive processes in design, etc. (Togelius et al. 2013). Adams and Dormans (2012) describe conceptual game-
Although we understand that each of these goals may be economic mechanics patterns that define how resources
important in specific game development or research con- flow through a system, and patterns to engineer gameplay,
texts, we believe that for successful game development, the e.g., choice, trade-off, friction, mitigation. Van Rozen
quality and coherence of the generated results is critical. (2015) describes a mechanics design assistant that leverages
PCG allows game developers to create an experience where these patterns for live programming of game economies by
players cannot rely on previous experience with the same generating them into running games.
content, creating an experience that is different from games Our pattern language represents a new category that
where all levels are pre-designed. But this works best when introduces applied Appraisal Theory to create high-level
certain standards are met in the generated levels (Rozen & emotional patterns and low-level appraisal patterns that
Heijn 2018). As is the case with mixed-initiative approaches steer the content generation towards structures we relate to
to PCG (Smith et al. 2011; Karavolos et al. 2015), we are desired emotional effects.
interested in how PCG can change and improve the process
of game development when concrete design knowledge, in
Design Patterns for Emotional Effect
this case the application of Appraisal Theory, is codified in
the generative process. Following the approach of design patterns, combining
elements from different design pattern templates and
Modelling Emotions approaches (Bacher 2008; Björk & Holopainen 2003;
Theories on emotional process include categorical (Ekman Gamma et al. 1995; Hullet & Whitehead 2010; Lemay 2007;
1992), dimensional (Plutchik 2001), and appraisal theories Will 2013), we propose a template format for design pat-
(Ellsworth & Scherer 2003). Appraisal Theory seems well- terns specifically for emotions and appraisals, consisting of
suited to our goals due to its ability to explain underlying the fields listed in table 1 and table 2, respectively. Next, we
causes of emotions while other theories mainly focus on cat- present examples of both kind of patterns.
egorization of emotions. Also, sources on emotions in
games mention Appraisal Theory as basis to understand how Appraisal Patterns: Centering
to affect emotions (Yannakakis & Paiva 2014). Appraisal patterns support the emotion patterns by describ-
Appraisal Theory states that “…people’s emotions arise ing how to use composition, structure and meaningful
from their perceptions of their circumstances – immediate, objects in abstract solutions to realize the relevant apprais-
imagined, or remembered” (Ellsworth & Scherer, 2003, p. als. Patterns currently formulated within the language are
572). A certain event, in relation to the one involved, is eval- Centering, Pointing Out, Appearance of Objects, Frame by
uated or appraised leading to an emotion (Smith & Lazarus, Surrounding, Content Density, Symmetry, Just Not Symmet-
1990). The different possible appraisals one can make have ric, Rewards, Rare Sightseeing and Conflict. The Centering
been classified in the appraisal dimensions (Ellsworth & pattern is presented in Table 3 as an example.
Scherer 2003). Each of these dimensions is appraised sepa-
rately, resulting in a specific value for the dimension, i.e., an Patterns for Emotions: Fear and Wonder
appraisal. An example of such a dimension is Novelty, which Based on Appraisal Theory, specific emotions arise from a
can be appraised as high or low or everything in between. A specific set of appraisals. Therefore, by combining multiple
specific set of values for each dimension then leads to a spe- patterns for appraisal, a pattern for emotion can be applied.
cific emotion. For example, in Table 4, the design pattern for the emotion
Wonder is presented. The solution part of this pattern,
depicted in Figure 1, shows the required appraisals (Novelty, Table 3. Design pattern for Centering.
Pleasantness and the negation !Urgency), together with
Name. Centering
potential ways to realize these appraisals in a particular
Problem. How to make an element of interest stand out in a level.
form. The appraisal Novelty can be realized, for example, by
Forces. The element that should capture the attention has a particular
Centering or Pointing Out the novel object, or by Frame by
importance or amount of focus, such that it stands out while all other
Surrounding.
objects are not completely overlooked. The more diegetic the way of
Table 1. Design pattern template for Emotion patterns. drawing attention is, the better it fits the experience. The size of the
element is important, since it can be hard to make small elements stand
Field Description
out. The surroundings influence the ease at which something can be
Name A descriptive name with which the pattern can
be uniquely identified and referenced to. made stand out and its resulting effect. Patterns triggering novelty
inhibit emotion patterns that require the absence novelty.
Problem The emotion to affect.
Context. A particular object, group of objects or other applied pattern
Core relational The core of the emotion captured in one
should capture the attention. A separated area pattern has been applied
theme sentence.
to the level, and the resulting area is large enough to consist of the object
Forces The considerations that must be taken into
to capture attention and center things inside. Importance: the amount of
account when implementing the solution.
focus this pattern can provide is medium to high, depending on the size
Context The circumstances and constraints of the
situation in which the given problem occurs. and the surroundings. Diegetic: the implementation is diegetic but can
be influenced by the surroundings. In some situations, it is not natural
Participants The different patterns involved in the
application. to center a specific element. Size: the size of the element of interest is
at least medium and can be greater in relation to the other objects in the
Required The appraisal dimensions and their values
appraisals required to affect the given emotion. surroundings. Surroundings: the surroundings of the application of this
pattern allow for centering by consisting of an area that stands out in
Solution The possible combinations of appraisal
patterns for each required appraisal, captured such a way that it can be recognized as a separated area. All other forces
in a diagram as shown in Figure 1. are influenced by the surroundings.
Related patterns The relationships this pattern has with other Participants. Object of focus: the object, or group of objects, that
patterns including the type of relationship. captures the attention. Area: the available space, defined the applied
Example An example in which the pattern is applied separated area pattern, to place the object.
within the game. Affected appraisals. Novelty: medium – high
Solution. Place the object, or group of objects, to stand out in the center
Table 2. Design pattern template for Appraisal patterns. of the area created by the applied separated area pattern.
Field Description Relations. Requires a separated area pattern to create an area to focus
Name A descriptive name with which the pattern can in. Reinforces other novel objects patterns and rare sightseeing since
be uniquely identified and referenced to. applying those together results in a higher novelty. Extends symmetry,
Illustration The essence of the pattern captured in an just not symmetric and rewarding resources since it adds novelty to the
illustration. effect of those patterns.
Problem The appraisal to trigger. Example. In the game currently under development, scrying points are
Forces The considerations that must be taken into a way of exploring the surrounding locations quickly. Such a point is
account when implementing the solution. indicated by a pillar-like object placed somewhere in the level. To make
Context The circumstances and constraints of the this object capture more attention and stand out, it can be centered
situation in which the given problem occurs. within a frame. A variety of options can be used to create the frame: the
Participants The different objects and their respective roles area itself can be formed in a symmetric, basic shape, or a circle can be
involved in the application. created with flowers.
Affected The appraisal dimensions and their values Variations. Place the object on the edge of the area. Note that this is
appraisals affected by this pattern. only possible if you can center on the form of the given area.
Solution The proposed solution for the given problem in Inspirations. Metropolis – Ralph Koltai: The elevator – which rises
the given context. into the city above in act I – is centered in the middle of the ground
Related patterns The relationships this pattern has with other (Davis 2001, p. 36). The Ring Thing – Don’t Starve: The Ring Thing is
patterns including the type of relationship. one of the ‘things’ the player needs to find to progress onto next worlds
Example An example in which the pattern is applied in Don’t Starve. Each of these things are centered in a clearly identifia-
within the game. ble, primitive form. The Ring Thing is centered in a circle with plants.
Variations Multiple variations on the solution. This circle functions as frame and the Ring Thing could not be centered
Inspiration An overview of games, art works, etc. that without it (Klei Entertainment 2013).
inspired to capture this pattern.
Table 4. Design pattern for the emotion Wonder. The appraisal Pleasantness can be realized using Symmetry,
or by presenting a Rare Sightseeing, or by Rewarding
Name. Wonder
Resources. To give an example of another emotion that has
Problem. How to evoke wonder in a given part of a level.
been formulated in our pattern language, Fear requires a
Core relational theme. Interest in the unusual or extraordinary.
different set of appraisals, including relatively high Novelty,
Forces. Emotions can vary in intensity. A higher intensity will not only
Urgency, Outcome probability, Conduciveness, but no or
cause the emotion itself to be stronger but will also increase the number
low Pleasantness, Adjustment and Power, and Agency
of different players actually experiencing the desired emotion.
associated with other actors than the player.
Some emotions lose their impact when they are experienced more often.
They are also experienced more fully when they are alternated with
other emotions. One cannot experience joy forever for it would become Level Generation
the norm. Therefore, the amount of usages of patterns of emotions is
correlated with the impact of it. As a proof-of-concept, a design pattern for emotional effect
Context. The whole level or a particular part should give the player the and its associated appraisal patterns have been implemented
sensation of wonder. Intensity: the intensity heavily depends on the to generate appealing content in the form of levels for the
selected low-level patterns and the application of those low-levels. To game currently in development (The Sequel to Unexplored),
increase intensity further, low-level patterns affecting the same using generative grammars in Ludoscope (Dormans 2011),
appraisal can be combined. Amount of usages: since wonder captures a which provides output to the Unity game engine. Although
feeling of surprise, an unusual feeling, the amount of usages should be the emotion and appraisal design patterns are generic, the
limited and alternated with other emotions. rewrite rules that place the patterns in the tile map are appli-
Participants. The selected appraisal patterns and their participants. cation dependent since specific structures and shapes are
Required appraisals. Novelty: medium – high. placed with specific tiles. The level generation process is
Pleasantness: medium – high. depicted in Figure 2, in four steps, from top to bottom:
Urgency: none – low.
Solution. See Figure 1. A. The patterns are placed in the graph, indicated by
Example. A moment of wonder can be created in the game under purple nodes, as is the participant, indicated by a
development by triggering all the listed appraisals. The player walks yellow node. The blue edges indicate the order in
through the mountains when suddenly the pebble path changes in an old which the patterns and participants must be resolved.
road with tile patterns, triggering novelty by appearance of objects. The B. The patterns (and other features) are positioned and
surroundings are flattened and surrounded by pillars, which increases structured within the tile map, based on a recipe (an
novelty with the use of the frame by surrounding pattern. Large statues ordered set of rules) created from the graph.
of faces are artifacts of an ancient civilization and, although they spawn C. After some intermediate steps, all non-terminal
a number of times in a world, they are quite rare. One is placed in the symbols are resolved to terminal symbols.
center of the frame, which further increases novelty with the centering D. Unity interprets the level and places all objects
pattern, and adds pleasantness using the rare sightseeing pattern. accordingly, resulting in a graphical scene to be
presented in the game.
Since the application of the Wonder pattern is a matter of
combining low-level patterns that affect those appraisals,
with only a few different low-level pattern implementations
variations can easily be realized. For example, in Figure 2D,
Wonder was realized by Frame by Surrounding (circle of
objects) with Rewarding Resources (experience points) and
Centering (scrying point in the middle of the frame), but the
Centering and the Frame by Surrounding patterns could
have been instantiated using other game objects, and instead
of Rewarding Resources, other realizations of the Pleasant-
ness appraisal could have been selected.
Some patterns are placed with one rule, such as the
Centering pattern which only marks the center tile. Other
Figure 1. The solution part of the design pattern for Wonder, patterns are placed with a sequence of rules that build up the
including appraisals and potential ways to realize them. pattern in a stepwise manner, such as the Frame by
Surrounding pattern. After a pattern is placed, interesting lo-
cations remain marked so participants can be placed later on.
Discussion
Generality and Scalability
Our approach is generic, but allows for domain- (i.e., game)
specific extensions. The design patterns for emotions and
A appraisals can also be applied in procedural content genera-
tion for other games, or even other multimedia applications.
To cater for specific uses, users need to adapt the rules
that specify how appraisals can be realized using elements
of that particular game or application. When the elements
are similar between games, the rules will be similar too. If
other emotional effects are desired, new patterns can be
added for those, without the need to change others. The
appraisals for many emotions partly overlap, which means
that the work done for these appraisals can be reused.
A content generation system that is able to achieve many
different emotional effects, will need many rules, which
increases its complexity and introduces new development
and maintenance challenges. However, the specification of
design intent in the design patterns makes the approach more
modular and scalable than is often the case in procedural
B content generation systems; many rules will be variant
implementations of basic appraisals, which in turn can be
easily assembled into higher-level patterns. The modularity
of the approach keeps the complexity under control, even
when working with a large number of implemented patterns.
In addition, the design patterns facilitate a separation of
concerns for the different responsibilities of a sophisticated
content generator. The proposed patterns direct the imple-
mentation of high level design goals for individual levels or
level sections. The responsibility for what those design
goals might be can be placed elsewhere, either with a differ-
ent expert algorithm, a human designer, or something as
simple as randomly selected design goals.
Direction as Underspecified Situated Context
In our approach we use design patterns as a means to capture
C and express design intent explicitly. However, rather than
specifying what needs to be generated, we view design
intent as setting goals and necessary constraints, leaving
ample room for unexpected variation in content and form.
We consider our approach analogous to the guidance
given by a director in improvisational theater sports. In such
a context, directions are typically not expressing what needs
to be said or done directly, but rather the effect to be
reached, or constraints to be taken into account. This leaves
the result underspecified, which often leads to surprising
D outcomes. We view procedural content generation in a
Figure 2. Level generation process, from A (top) to D (bottom).
similar vein, not specifying directly what needs to be
generated, but rather the effect to be achieved, and multiple Conclusion
methods for achieving it, so that the results may still surprise
the designer too. This study explored the feasibility of formulating design
patterns for emotion in level design and the implementation
Preliminary Evaluation of the resulting patterns in generative grammars for level
generation. Using Appraisal Theory as a theoretical founda-
To assess whether the approach is feasible, the generated
tion, design patterns were presented for emotions such as
levels were evaluated in a meeting with three professionals fear and wonder, and their required appraisals, which
from the game industry. The experts confirmed the value of describe how to use composition, structure and meaningful
the insights gained in this study, and that the implementation objects in abstract solutions.
approach of patterns in generative grammars is valuable. According to Appraisal Theory, appraisals are made
Nevertheless, the implementation should be more promi- regarding the relationship between the event and the person
nent. Several promising improvements were suggested, e.g., involved and, together, they support the occurrence of an
applying multiple appraisal patterns per required appraisal emotion. This theory depicts the structure of the presented
or creating anticipations and expectations. pattern language in which appraisal patterns (triggering ap-
Additionally, the experts suggested that the current pattern praisals) are combined to apply emotion patterns (affecting
language should be supplemented by taking into account emotions). An approach was proposed to implement such
elements that contribute to creating overarching experi- design patterns, expressing how rewrite rules can be created
ences. Interesting elements to explore are the surroundings by increasingly adding features to and removing abstraction
and the context of a pattern, the expectations and the antici- from the level, resulting in an applied pattern.
pations of the player, pacing between emotion patterns and To prove the feasibility of implementing such patterns, a
the perception of the game world. More thorough validation, procedural level generator was implemented for a game
and evaluation through playtesting is part of future work. currently in development, using an approach based on
generative grammars. Preliminary evaluation with three
Limitations experienced game designers has indicated that it is possible
Applying and extending and implementing the pattern to create moments in which a given emotion is suggested.
language is work in progress. We identify the following From a technical point of view, the use of the design patterns
bottlenecks and actionable steps: structures the content generator in such way that different
• Recognizing shapes with variable sizes and consistency. concerns are handled by different components. This results
• Obtaining information about objects in the surroundings, in an architecture that is modular and scales well enough to
such as the average color or size. accommodate the amount of content that is required for a
• Influencing the surroundings of a pattern. commercial game.
The main contributions of this paper are (1) a new frame-
• Providing sufficient variations and possible combinations work for capturing design intent as direction in grammar-
of patterns to prevent recognizable repetition. based procedural level generation (2) the proposed pattern
language for design patterns for emotions and the required
Future Work appraisals, and (3) the implementation of a level generator
Further work on the pattern language includes the addition that allows the game designer to play the role of a level
of more emotion and appraisal patterns, and improving the director wishing to achieve emotional effects. These contri-
implementation of patterns in generative grammars by butions are considered valuable for the research field of
addressing the limitations mentioned above. When the main procedural generation of content for games and other inter-
implications have been identified and addressed, validation active media. This is especially true when an approach is
of the pattern language with more game design experts from taken that involves design intentions, or when emotional
research and industry is desired, as well as playtests with effects are desired. The theoretical foundation of Appraisal
users to analyze the actual emotion effects, to further Theory allows for logical design choices that allow extend-
improve the language and the implementation of patterns. ing the pattern language with other emotions.
Future research could focus on other elements that seem Recommendations for future work include expanding the
important for affecting emotions within the overarching current set of patterns, addressing the limitations that were
experience of playing a game, such as pacing, perception, identified for the pattern implementation, validating the
anticipation and expectation. pattern language within a wider community of practitioners
and researchers, and exploring the aspects in games that
influence overarching experiences of emotional dynamics.
Acknowledgments Hullett, K., & Whitehead, J. 2010. Design Patterns in FPS Levels.
In Proceedings of FDG 2010 (pp. 78-85): ACM.
This research has been carried out in the context of the ‘Live Game Karavolos, D., Bouwer, A., & Bidarra, R. 2015. Mixed-Initiative
Design’ project, which is subsidized by the Dutch funding body for Design of Game Levels: Integrating Mission and Space into Level
applied research NWO-SIA. In addition, we thank indie-game stu- Generation. In Proceedings of FDG 2015.
dio Ludomotion for supporting this research.
Klei Entertainment. 2013. Don’t Starve [Game]. Vancouver, Can-
ada.
References Lemay, P. 2007. Developing a Pattern Language for Flow Experi-
ences in Video Games. In Proceedings of DiGRA 2007 Confer-
Adams, E., and Dormans, J. 2012. Game mechanics: advanced ence.
game design: New Riders, Berkeley, CA. Lövheim, H. 2012. A New Three-Dimensional Model for Emo-
Alexander, C., Ishikawa, S., & Silverstein, M. 1977. A Pattern tions and Monoamine Neurotransmitters. Med. Hypotheses 78:
Language: towns, buildings, construction: Oxford University 341–348.
Press, New York. Plutchik, R. 2001. The Nature of Emotions: Human emotions have
Bacher, D. 2008. Design Patterns in Level Design: Common Prac- deep evolutionary roots, a fact that may explain their complexity
tices in Simulated Environment Construction. Retrospective The- and provide tools for clinical practice. American Scientist, Vol. 89,
ses and Dissertations, Paper 15345: Iowa State University. No. 4 (July-August 2001): 344-350.
Björk, S., Holopainen, J., & Lundgren, S. 2003. Game Design Pat- van Rozen, R. 2015. A Pattern-Based Game Mechanics Design As-
terns. Digital Games Research Conference 2003, 4-6 November sistant. In Proceedings of FDG 2015.
2003, University of Utrecht, The Netherlands. van Rozen, R., & Heijn, Q. 2018. Measuring Quality of Grammars
Björk, S., and Holopainen, J. 2004. Patterns in Game Design for Procedural Level Generation. In Proceedings of FDG 2018.
(Game Development Series): Charles River Media, Rockland, MA. Shaker, N., Liapis, A., Togelius, J., Lopes, R., & Bidarra, R. 2016.
Will, C. 2013. A Pattern Language for Designing Location-Based Constructive generation methods for dungeons and levels. In Pro-
Games: Aachen University. Retrieved Feb 18, 2018, from cedural Content Generation in Games: 31-55: Springer, Cham.
https://hci.rwth-aachen.de/materials/publications/will2013a.pdf. Smith, C. A., & Lazarus, R. S. 1990. Emotion and Adaption. In
Davis, T. 2001. Stage Design. Rotovision, Hove, United Kingdom. Pervin, L.A. (ed.), Handbook of Personality: Theory and
De Melo, C. M., Paiva, A., & Gratch, J. 2000. Emotion in Games. Research: Guilford, New York: 609-637.
In Agius, H. and Angelides, M. (eds.), Handbook of Digital Smith, G., Whitehead, J., and Mateas, M. 2011. Tanagra: Reactive
Games: 573-592:Wiley. Planning and Constraint Solving for Mixed-Initiative Level De-
Dormans, J. 2010. Adventures in Level Design: Generating Mis- sign. IEEE Transactions on Computational Intelligence and AI in
sions and Spaces for Action Adventure Games. In Proceedings of Games (TCIAIG), Special Issue on Procedural Content Generation
the 2010 workshop on procedural content generation in game: 3, 3.
ACM. Togelius, J., Champandard, A. J., Lanzi, P. L., Mateas, M., Paiva,
Dormans, J. 2011. Level Design as Model Transformation: A Strat- A., & Stanley, K. O. 2013. Procedural Content Generation: Goals,
egy for Automated Content Generation. In Proceedings of the 2nd Challenges and Actionable Steps. In Artificial and Computational
International Workshop on Procedural Content Generation in Intelligence in Games, Dagstuhl Follow-Ups, Volume 6.
Games: ACM. Tomkins, S. S. 1995. Exploring affect: the selected writings of Sil-
Ekman, P. 1992. An Argument for Basic Emotions. Cognition & van S Tomkins: Cambridge University Press.
emotion, 6(3-4): 169-200. Treanor, M., Schweizer, B., Bogost, I., & Mateas, M. 2011. Proce-
Ellsworth, P. C., & Scherer, K. R. 2003. Appraisal Processes in duralist Readings: How to find meaning in games with graphical
Emotion. In Davidson, R.J., Goldsmith, H., & Scherer, K.R. (Eds.), logics. In Proceedings of FDG 2011.
Handbook of Affective Sciences: Oxford University Press, New Yannakakis, G. N., & Paiva, A. 2014. Emotions in Games. In The
York: 572–595. Oxford Handbook of Affective Computing: 459-471.
Game Ontology Project, https://www.gameontology.com Zagal, J.P., Mateas, M., Fernández-Vara, C., Hochhalter, B. and
Gameplay Design Patterns, http://www.gameplaydesignpat- Lichti, N., 2007. Towards an ontological language for game anal-
terns.org ysis. Worlds in Play: International Perspectives on Digital Games
Research, 21: 21
Gamma, E., Helm, R., Johnson, R., & Vlissides, J. 1995. Design
Patterns: Elements of Reusable Object-Oriented Software: Pear-
son Education India.