Introduction

When talking about the process of game design, many people think that the creation of a game is somehow similar to other building processes, such as making a technological device, writing a book or producing a report. Sometime this is true, but the majority of the game design processes relies often on a different approach. The most common approach used to write a book is called the top-down method, while the common approach in game design is the bottom-up, this because writing a book can be often a linear process, while creating a game is not. For this reason, when it's necessary to produce a narrative to create a background story for a game, in many cases the bottom-up approach is the best choice.

This article wants to compare these two approaches in the game design context, by highlighting the pros and cons of each method, and providing an example about how to bind the game mechanics and the narrative using the bottom-up approach. This discussion should be related to the the ludology vs. narratology debate, which is considered a very important issue by game-design experts.

Table of contents

• Top-down and bottom-up approach
• A first comparison between the top-down and bottom-up approach
• Example - Introducing Real Time Strategy video games
• Example - Building game missions for a RTS video game
• Example - Adjusting the design of a RTS video game
• Example - Writing the narrative of a RTS video game
• Conclusions

Top-down and bottom-up approach

In the top-down approach you could begin by creating an outline of the document you'd like to produce, defining the overall structure of the final product, the main sections, topics or issues that you want to talk about, and then you start writing the necessary paragraphs. When working within a team this method is useful if the person writing the outline (usually the manager or the boss) wants to define the overall structure of the product, leaving to other people to fill the details. This process is often (but not always) used in Object-oriented programming, when a senior developer codes the signatures of the necessary functions, allowing the junior developers to focus on the details (that's called implementing the software).
Top-down approach

In the game design context the top-down approach means writing the overall narrative first, and then creating the specific game scenarios, game mechanics and game events fitting that narrative. We could say that the top-down approach presents these features:

• Creative when writing the narrative, by allowing complete freedom
• Providing some guidelines for writing the single game scenarios
• The game mechanics should be selected among those better fitting the narrative's requirements

The bottom-up approach could mean writing a book by writing the single chapters first, without having in mind the whole story, and then fitting all these chapters together as long as they become available. Kids use this process where playing to the random words game, where the participants just share random words, without having the big picture in mind, since the big picture will be the outcome of the process.
In the game design context the bottom-up approach means writing the game scenarios, game mechanics and game events first, and then writing a narrative putting together all the game elements. We could say that the bottom-up approach presents these features:
Bottom-up approach

• Creative when writing the game scenarios and defining the game mechanics
• Providing some guidelines for writing the overall narrative
• The game mechanics can be selected among all those technically available

A first comparison

To define a game concept and the relative narrative, the top-down approach could be useful if there isn't any constraint about the game mechanics (or the game technology). In such a case should be always possible to write the narrative first and then starting designing the single game sessions. As long as the game sessions will be designed, it should be possible to define all the necessary game mechanics and better define the game concept. We could say that such approach is narrative driven, since the narrative will be used to select the game mechanics, to specify the game concept and - if we're speaking about video games - to choose the best fitting game technology.

On the opposite, when the game design starts from some ideas concerning the game mechanics or the game technology, then the bottom-up approach could be the best one. The game designers could start by defining the available game mechanics and creating all the scenarios aimed to exploit such mechanics. Then, when all the game scenarios are completed, some creative work is necessary to put all the pieces together, eventually tweaking the single game sessions. In this case we could say that the process is game play driven or technology driven.

A common criticism to the bottom-up approach is that without the overall frame (the narrative) it's difficult to design the single game sessions. This is often a wrong interpretation of the actual issue: the bottom-up approach allows too much freedom in the first design stage, and having too much freedom sometimes could be confused with having no ideas.
Game design aspects

A solution could be to forget (in the first stage) that each single game session will be bound in future with all the other game sessions, and to focus on the specific single game session as if it was a stand-alone game.
In other words, thinking about the overall narrative - when designing a single mission - means mixing together the top-down and the bottom-up approach, losing all the benefits of the two methods.

Example - Introducing Real Time Strategy video games

To provide an example of a game design relying on the bottom-up approach, we'll consider a very common genre of video games: the Real Time Strategy video game (RTS). In the last 20 years hundreds of these video games have become very popular, for example: Stronghold, Warcraft, Homeworld: Cataclysm, Rise of Legends and many others.

When playing these games it's easy to browse "what's under the hood" and discover that probably many of these games have been designed using the bottom-up approach. This notion arises from the fact that all these games present a very similar structure for the game mechanics, which could be sketched out as follows:

1. Browsing map and panels: the player can browse a map, or check some panels, to acknowledge the status of his kingdom, country or army. These panels should allow the player to control the amount of available resources, population, money budget, energy or whatever is used to describe the current status of the game.


2. Collecting resources: the player must collect some specific resources, for example wood, stone, food, minerals or fuel, depending by the game background and overall setting. These resources will allow the player to activate the other game mechanics (listed below).


3. Place buildings: spending resources the player can build new buildings or specific vehicles. Usually in the first stage of the game these buildings or vehicles will just improve the collection of resources and will defend the player from the enemy.


4. Manage population: spending resources and using the new buildings the player can increase his population, this could allow the economy to grow or the player to start organizing an army. This game mechanic is not always available, but it's very common.


5. Research budget: spending resources or assigning budget (or human resources) to specific buildings the player can start new scientific researches that will improve the cultural and technological level of his kingdom or country. Usually this allows the player to create more advanced buildings, having a better economy, solving population problems or creating more advacend weapons and soldiers. This game mechanic is not always available, but it's very common.


6. Trade: sometimes specific researches outcomes, or some advanced buildings, could allow the player to trade resources or weapons. This commerce could involve some A.I. character, the enemy itself or just general purposes market place.


7. Counter the enemy: even with just few soldiers, weapons or war-oriented buildings the player could be faced to defend from the enemy attack. Usually this implies using in a very specific way some game mechanics, like building fences, placing traps, using archers, rifleman or energy shields, depending by the overall game setting. Usually these game events happen within the player's kingdom


8. Fight the enemy: when the player managed to organize more soldiers, war machinery or an entire army, he can attack the enemy in order to get score points, to try winning the game session or even to pillage resources from the enemy. Usually these game events happen far from the player's kingdom, by moving the army trought the enemy territory


9. Advanced features: using the advanced buildings, the researches outcomes and the improved economy the player could be able to produce very specific machinery, devices, equipment or weapons. This could include, for example, the capability to manage diplomatic issues, building very advanced vehicles, sending spies in the enemy's territory, starting social or religious revolutions etc.

In the next section we'll use this list to provide an example about how to bind the single game sessions and an overall narrative using the bottom-up approach.

Example - Building game missions for a RTS videogame

Let's assume that we want to create a new RTS game starting from the game mechanics listed above, without having any narrative in mind. This means that we're going to use the bottom-up approach. Before starting we need to decide the overall background setting, that could be an historical setting, a fantasy setting or even a science-fiction setting. In this section we'll offer two different examples regarding two different scenarios: a medieval setting and a science-fiction setting. Having two completely different scenarios should easy understanding that we're starting from the bottom (the game features) and "moving up" the process: we'll start from the same game mechanics (the bottom layer) then we'll move up, designing the single game sessions (the middle layer), and finally we'll end up with something specific for that setting. To do this we'll assume that we already designed all the game mechanics, that will be the game mechanics listed above.

Before proceeding, let's notice that the game elements managed by these mechanics will be very different, for example

Game elements	Medieval setting	Science-fiction setting
Resources	Wood, stone, gold, food, etc.	Minerals, crystal, fuel, energy, etc.
Buildings	Stronghold, granary, barracks, etc.	Spaceship, hangar, laboratory, etc.
Weapons	Arch, sword, boiling oil, etc.	Machine gun, bombs, laser, etc.
etc...	etc...	etc...

Now we want to create all the single game sessions, and we'll call them also episodes, missions or single scenarios. A very common practice is to design these missions following the order given by the difficulty of the game mechanics, because by doing this the final set of missions will be also an interactive tutorial to the game itself.
This is a very import issue, because RTS games can be played in many different ways, and not only following the narrative. For example, RTS games can be also used to play one-shot game session (fighting against an A.I. character) or one-shot sessions fighting against human player (when used in the multi-player mode).

We can finally start to create all our missions! In the next table we'll show, for the two considered scenarios, all the game missions related to the same game mechanics listed above, and how from all these missions it's easy to obtain a well-fitting prelude story.

Game mechanics	Medieval setting	Science-fiction setting
Browsing map and panels	Mission: the player must find the enemy position on the map and, using this information, he must reorganize the policy of his kingdom. Prelude: you are the prince of the Galash Kingdom. Few days ago your ancient enemy, the Kingdom of Snake, attacked your territory and pillaged your castle. You, with just few guards, managed to escape from the burning castle. Your father, king George, has died in the fight, and you promised to revenge against you enemy, the the Kingdom of Snake. This will not be an easy task, because king Silver of the Snake has left his country and now he's hiding somewhere. Moreover, all your citizens are scared and confused: you must discover the enemy position and reorganize your kingdom. Revenge is a dish best served cold.	Mission: the player must find the enemy position on the map, and, using this information, he must reorganize the policy of his spaceship. Prelude: in 2215 the Earth has huge overpopulation problems. Few days ago, the mysterious creation of a new space-time wormhole next to the Moon offered to the human race a chance to explore the farthest sections of the galaxy. You are the captain of the first spaceship traveling through the wormhole to explore what's on the other side. But when you just passed through the wormhole, some alien spaceships attacked you. You managed to escape from the fight, but the enemy's bombs hit the wormhole and the passage collapsed. Now you are on the other side of galaxy, far from home, all alone! Your first task is to identify the enemy position and to reorganize your ship to survive in a new hostile environment.
Collecting resources	Mission: the player must collect a given number of resources. Prelude: after discovering the enemy position and having reorganized your citizens, you realize that the situation is very dangerous. The enemy pillaged all your resources, and your citizens are starving. You must collect the wood and stone necessary to rebuild new houses, and the food allowing your people to survive.	Mission: the player must collect a given number of resources. Prelude: after having reconfigured your spaceship, you managed to hide from the enemy. But your ship was aimed to travel for just few days, and now you are running out of energy. Fortunately, few minutes ago your radar detected some rocks rich of minerals. You must collect all the minerals and convert them into energy to survive in the deep outer space.
Place buildings	Mission: the player must build a barracks building. Prelude: the collection of resources has been very successful! Now you can even try to build a new barracks building, that will allow you to defend from the enemy. But to do this you will need to collect also some iron from the mountains, which means collecting resources in a very dangerous territory...	Mission: the player must build a new hangar bay. Prelude: the collection of resources has been very successful! Now you can even try to build a new hangar bay, that will allow you to send small finders ships to explore the outer space. Building an hangar bays means reorganizing again your spaceship, hence some more resources could be necessary.
Manage population	Mission: the player must reach a given number of citizens. Prelude: now that the barracks building has been completed, your started to enroll new soldiers, but in few days a new problem arises! Converting citizens into soldiers reduced the number of workmen and farmers, and now your people is starving again. Listening to your counselor, the economy of your kingdom is too small and you can not afford soldiers. A solution could be to increase the population by encouraging immigration into your kingdom, in order to have new workers and a bigger economy.	Mission: the player must reach a given number of pilots. Prelude: now that the hangar bay has been completed, your started to produce new fighter ships, but then you realized that you don't have enough pilots. Since the number of people on your ship can't grow, you decide to convert all the robots aimed to analyze the wormhole into pilots, since the wormhole does not exist anymore. Training robots to become pilots it's not an easy task, but managing your human resources you should be able to get some good teachers.
Research budget	Mission: the player must discover the power of magic. Prelude: in the meanwhile that your first soldiers are practicing, a bard arrives into your kingdom and start telling incredible stories about the Kingdom of Snake. If these tales are true, King Silver discovered your position and he's going to attack you soon! Moreover, thanks to the result of some new mysterious science, it seems that the enemy will use new powerful weapons to attack you. Your counselor suggest you to spend some resources to support the magic research, because only magic could counter the enemy's weapons in such a short time!	Mission: the player must discover a new technology. Prelude: in the meanwhile that your first robot pilots are practicing, your scientific officer report you that a strange electromagnetic anomaly has been detected near the enemy position. Perhaps the enemy is looking for you or, even worse, he's testing a new terrible weapon. Your scientific officer suggest you to spend as many resources as possible to complete some scientific experiments that have become possible after passing through the wormhole. If his theory is right, in just few days you could discover a new fantastic technology!
Counter the enemy	Mission: the player must defend his territory from the enemy's attack. Prelude: finally your first soldiers are trained and magic begins to flow within your kingdom when ... some swordsman attack your farmers to pillage you again! You command all your soldiers and your wizards to counter this attack, since you can not stop collecting resources. Your counselor suggest you to place the soldiers on the front line and the wizards on the back line, because only with this formation you can beat the enemy.	Mission: the player must defend his miners from the enemy's attack. Prelude: finally your first robots are trained and the reports coming from the scientific researches are very optimistic when ... some unknown fighters start to attack your miners! You command all your fighters to counter the enemy and defend your miners, since you can not stop collecting resources. Your tactical officer suggest you to move the fighters in a delta formation, because this should allow you to launch missiles without any risk to hit your own ships.

Oops ... there's something weird, here: we wrote the mission about countering the enemy before the trade feature!
Is anything wrong with this? No, it isn't! We are going this discuss below...

Example - Adjusting the design of a RTS video game

The top-down approach and bottom-up approach are intended to be guidelines to easy the game design process, and must not be used as strict rules nor mandatory frames. It's very common, when coming to the details of the game design, having new ideas that could improve to the whole process.
In the top-down approach, for example, this happens when you finish writing a chapter and you realize that you wrote something different from what stated in the chapter's header. If what you wrote it's better than the content you had in mind at the beginning, of course you could consider to change the chapter's title, instead of rewriting the chapter.

In the bottom-up approach this happens when you are working at the lower layers (the game mechanics or the storyline preludes), and you get some unexpected ideas. Let's consider the example above, where we designed the enemy's attack before introducing the trade-oriented mission. Trying to answer to the question "how can I introduce the trade mission now?", some brand new ideas could emerge. Here they are:

What if the soldiers that attacked that player were not from the original enemy, but from another country, race or kingdom? Maybe they tried to pillage the player because they were starving, and they were starving because they have been also attacked from the original enemy, the one that attacked the player in the first prelude. This could lead to a narrative where the player can discuss an alleance with this new faction, and this could mean having a more realistic narrative, where the player's final victory will not be just an effect of controlling a bigger territory, but to be consequent upon the trade agreements reached with other people.

What if the soldiers that attacked that player were from the original enemy, but they were just deserters attacking the player to get some food? This could suggest a narrative where the enemy's weak point is an open internal social conflict, hence the player must investigate this, sending people to ferment a civil war in the enemy's territory, in order to win the overall narrative without fighting a battle, but exploiting diplomatic strategies.

We could use one the ideas above (new potential rival or deserters from the original rival), but this could be just a disguise. We could tell one of the stories above for the time being, but we could reserve some surprise for the final end of the narrative.

Now we are going to design the last missions exploiting the missing game mechanics (trade, fight and advanced features), using some of these new ideas.

Game mechanics	Medieval setting	Science-fiction setting
Trade	Mission: the player must trade to obtain a specific number of resources he can not collect. Prelude: you successfully managed to counter the enemy's attack and you just discovered that those soldiers have not been sent by King Silver of the Snake! They are from the Diamond Shire, a small kingdom far away, and they were pillaged by King Silver too, few weeks ago! They are sorry for attacking you, and you forgive them. After a small celebration, you start considering the possibiliy to buy diamonds from the the Diamond Shire, because your wizards state that they could do better magic with a lot diamonds. Hence you decide to build a market place, where to trade different goods.	Mission: the player must trade to obtain a specific number of resources he can not collect. Prelude: you successfully managed to counter the enemy's attack and you captured all the enemy pilots. They all wear a very special space-suit that can not be removed, and admit to be aliens. They explain that they were ordered to attack you at the wormhole, but they regret it: they just attacked you because they wanted to desert, and they would like to join you! You are not confident about this, so you decide to keep them in the spaceship prison, but you want to be kind with them, by offering a trade: it seems that you prisoners could offer you access to a new kind of energy that you don't know at all...
Fight the enemy	Mission: the player must attack the enemy and pillage a given number of resources. Prelude: with the new power of your wizards and your army now you are ready to attack your the King of Snake. Your scout just reported that some enemy troupes are hiding next to Redville, a small village nearby your castle. This is a chance to test your fighting skills, and to give a first knock to King Silver. This will be a small battle, but could decide the future of your kingdom.	Mission: the player must attack the enemy and pillage a given number of resources. Prelude: if the information you bought from your prisoners are correct, your scientific officer can try to create a small wormhole tunnel which could allow you to teleport next to the enemy's position. This is a chance to test your fighting skills, and to give a first knock to the enemy. This will be a small battle, but could decide the future of the human race.
Advanced features	Mission: the player must develop a new technology to produce a special weapon. Prelude: after winning your first battle, you'd like to try to conquer the castle of King Silver and take your revenge. But listening to the advice of your new friends, the Diamond Shire, King Silver's castle has very hard walls and a deep ditch, so this will not be an easy task. Your counselor deems that if you assign some budget to his researches, perhaps he could manage to understand the principles of the trebuchet. With such a weapon, allowing you to destroy the enemy walls from a very long distance, victory could be yours!	Mission: the player must develop a new technology to produce a special weapon. Prelude: after winning your first battle, you'd like to try to attack the enemy. You need to conquer the original position where the first wormhole appeared, because only from that position you could try to go back home. But your prisoners suggest that you are not ready yet, because you know as to create a new wormhole, but you are not able to close one! Listening to their advice, you must be able to close wormholes before attacking the enemy, because this would prevent you from being attacked by surprise.

Finally we have designed all the missions and written a prelude to each mission. We wrote missions and preludes following the order above, to make sure to have some coherence among all the preludes. This makes really straightforward to put all the pieces together and to write the overall narrative, to complete our bottom-up design.

Example - Writing the narrative of a RTS video game

At this stage, having all the missions and all the preludes, the overall narrative is almost completely defined for both the settings (medieval-fantasy and science-fiction). We'll do this by "filling" some of the open issues arised when writing the mission, which could be.

Open issues in the medieval-fantasy settings

• Why are King Silver and King George enemies? Is there a need to specify this?
• Who are the bards helping the player? Why do they act like that?
• How can the player win the final battle? Is it realistic winning just because he discovered the trebuchet?

These open issues do not represent flaws of the bottom-up approach but, on the opposite, they are the entry points for writing the overall narrative! Let's try to do this, by focusing on the bards and the winning condition issues.

Narrative for the medieval-fantasy settings

The player is the Prince of Galash, a small kingdom ruled by his father, King George. The story begins when the kingdom of the Snake, ruled by King Silver, attacks and almost destroys the player's kingdom. King George and all the royal family are killed in the attack, and the player's castle pillaged and destroyed. The player wants to take revenge against his enemy, hence he must reorganize his citizens and collect new resources to build a new small castle. Then he must manage his people to increase population, conquering new territories, increasing the economy and discovering the secrets of magic.
In the meanwhile other countries and kingdoms are pillaged by the evil King Silver, and the refugees from these countries try to pillage the player in order to survive. The player must reach agreements with these other kingdoms and trade with them, while countering further attacks from the enemy.
Moreover the player receives also useful information from some bards visiting his castle, and with this information he will be able to attack the territory controlled by King Silver. But to win the final battle the player must discover a new weapon, the trebuchet, which will allow him to destroy the walls of the enemy's stronghold.
After many battles, the player manages to besiege the castle of King Silver of the Snake, but the enemy has an ace in the hole: King Silver throws many dead cows on the player's troops, and a terrible pestilence starts spreading among the player's army. But the bards, the ones who used to visit the player to report information, pop up again and start healing the sick soldiers. The bard reveals themselves as the Secret Order of the Druids of King George, and they know a secret passage leading inside the enemy's castle!
With the help of the druids the player manages to enter into the enemy's castle, opens the door and conquer the King of Snake. King Silver is captured and dethroned, and a new age of peace begins.

Let's now try to repeat this approach for the science-fiction settings.
The open issues arising from the preludes could be:

Open issues in the science-fiction settings

• Why do the aliens attacked the player? Is there a need to specify this?
• Why have some aliens deserted? Why they can not take off their space-suits?
• Why must the player attack the aliens? Perhaps it's more realistic just trying to go back to earth, by opening and closing a new wormhole!
• How can the player win the final battle? Is it realistic winning just because he discovered how to open and close wormholes? Perhaps the aliens should have a more advanced technology!

As above, these open issues are not flaws of the bottom-up approach but they are the entry points for completing the overall narrative: let's try to do this by introducing some space-time traveling adventures.

Narrative for the science-fiction settings

The player is the captain of the first spaceship exploring a mysterious wormhole appeared near the Moon in year 2215. The human race is suffering from overpopulation problems, hence the wormhole means the possibility to find new planets which could host human life. But just few minutes after the player's spaceship passes trought the wormhole, some alien spaceships attack the player and close the wormhole. In this fight the player's spaceship does not receive any damage, hence the player can focus on the challenge to reorganize the ship in order to survive in the outer space. Then he must collect new resources and update the ship design, because he needs other small finders and fighters spaceships to defend from the enemy. The player achieves this task by converting into pilots the robots that were assigned to exploring the wormhole, and doing some scientific research to learn how to open new wormholes. In the meanwhile, other alien's ship try to attack the player, but they surrender after a short fight: they claim to be deserters, and want to join the human race. Even if puzzled by the fact that the aliens can not remove their space-suit, the player trade with them, and this allows him to access a new kind of energy.
After few battles, the player manages to have a chance to attack the enemy's base, but before doing this the prisoners suggest him to learn also how to close wormholes, because this would prevent him from being attacked by surprise. When the player is ready to launch the final attack, the prisoners reveals themselves as ... being the player from the future! That's why they told the player that they could not remove their space-suit: they didn't want to be recognized! They tell the player that in the future the human race will be saved by this chain of events, because only after the accident of the first wormhole being closed the player's ship learned how to open and close wormholes, and this very technology will allow the human race to colonize other planets!
Hence the player must go back to were the first wormhole appeared, he must open it in the past and then he must attack ... himself from the past! By doing this he must be careful to destroy only fighters piloted from robots, to avoid killing human people. And the story repeats itself again, again and again, but each time the player plays a different role in the space-time continuum.

Conclusions

We can now summarize the bottom-up approach we used to write the narrative in the RTS video game example

1. We wrote down the list of the main game mechanics, which specifies the detailed game play features of the sample video game (bottom layer).
2. We created a custom mission for each game mechanic, with a target goal aimed to drive the player to exploit that mechanic. These game missions have been written independently, before having in mind any prelude or a storyline. This means that game missions could be developed by different persons within a team, working without any constraints, and could be produced in any order (middle layer).
3. We wrote a prelude for each mission, explaining why the player should try to achieve the mission's goal. We wrote all the preludes following a specific order, to make sure to have some continuity and coherence among all the preludes. This process can start only when all the missions have been developed, and should be carried on by a single designer or a well coordinated team work (middle layer).
4. The process of writing the last preludes for the game missions ispired new ideas, hence we tweaked a little the design of the game missions (and the corresponding preludes) for these missions.
5. Using all the preludes as a draft version of the game storyline, we wrote the overall narrative completing all the open issues, defining some missing elements and providing some long term narrative elements (top layer).

The tweaking process used to adjust the process it's not a flaw of the bottom-up approach, but it's a common practice of each design process, even in the top-down approach. For example, when writing a book, it's a common practice to adjust the title (and sometimes even the order) of the book's chapters when the book is completed. Sometimes, even the title of a book could be reviewed when the author finishes writing the book.

It's remarkable to notice that the bottom-up approach should be feasible also when designing Serious Games, because this should mean just adding a new layer on the bottom of the whole process, where we could put all the learning objectives of the Serious Game, which usually are defined after the assesment of the learning needs for the target users. Perhaps we could even suggest that, for what concerns learning tools, the bottom-up approach should be always the best one, because the most important elements of the learning process are the learning activities, where actual reflection and active participation take place. This implies that effective Seriuous Games should focus on the learning activities first, implemented by the game mechanics, and the overall narrative should be just a "beautifier wrapper" for all the specific game activities.

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