Monday, November 2, 2009

The Abstraction of Character Progress

The first post I made here on That’s a Terrible Idea documented the four core design elements of MMORPGs: conflict resolution, goal generation, power growth, and player interaction. In my 10 Points, I point out ways that each of these core elements will change in the MMO Revolution. We haven’t discussed these elements in much depth (aside from a couple posts regarding accountability systems to facilitate dynamic world player interaction). The recent discussion of use-based skill gain has caused me to return to these basic mechanics and spend some time analyzing the fundamentals of character growth mechanics.

RPGs are defined by the fact that as characters accomplish tasks in the game world they grow—and this growth is independent of the player gaining skill. There are two fundamental mechanics to character growth that all RPGs possess:

  1. Character advancement is granulized into some form of experience points. Experience points might be renamed, or be hidden, but they are always there in some form (even in Darkfall).
  2. Based on how many experience points characters have, characters unlock abilities and bonuses.

It’s obvious to someone who plays these games, but it’s crucial that this basis is understood. Now, we can get to the meat of the skill-based vs. level-based advancement debate: How continuous (or discrete) should advancement in RPGs be?

Power Curves

The gamut runs between the most discrete system, one where there is one transition in power level that happens instantaneously, to the most continuous system, one where every single action performed increases the success chance of the next action performed.

Discrete systems have clearly defined jumps in character power. These jumps are monolithic and all-or-nothing.

Continuous systems have a smooth gradient of power growth. There are many small jumps and these jumps are specific to certain facets of the character.

Class-centric level-based approaches are the most familiar and common RPG character growth schemes. This discrete scheme leads to a power curve that looks like this:


The step-like curve is the result of discrete changes in power linked to gaining character levels. It takes longer to level the stronger the character is, and there is less of an increase in power at each level. Max level is the only exception, where the character gets her endgame abilities which are usually a bit of a jump in marginal power gain from her abilities gained at max level minus one.

When advancement is localized to specific abilities, as in skill-based systems, a roughly continuous power gain results.


As the character interacts with the world, she continually gains ability in various areas, leading to a smooth power gain that marginally decays as time increases. In skill-based systems, the character is comparatively always gaining power.

The Results of Growth

Without some resultant effect on a character’s capability, growth is nothing more than a symbol (usually a number) of the character’s efforts in the game. In RPGs, growth is a primary positive feedback loop that rewards characters who accomplish important or impressive feats. At some point, growth grants a character abilities and effects.

Abilities are the actions the character can achieve in the game world, some of which are

  • Casting a spell
  • Performing a powerful melee attack
  • Making a bandage
  • Shooting a bow
  • Poisoning a weapon

Abilities are often arranged into ability groups—character classes are series of ability groups, one per level. Talent trees in World of Warcraft are ability groups. Ability groups allow access to be granted or denied to different sets of abilities. These grouping can be logical or mechanical. Logical groupings exist to allow the player to better conceptualize how abilities relate to one another, whereas mechanical groupings are higher-abstraction-level units of character capability that can be affected by different game mechanics. Tradeskills are a logical grouping of abilities, whereas fire magic is a mechanical grouping.

Effects are changes in the character’s stats, a passive bonus to that character’s capability. An increase in strength or vitality, for instance, is an effect.

The Scope of Experience

Experience points are the most common name for a resource that symbolizes growth. Growth resources alone account for several crucial design decisions:

  • What will grant experience points?
  • What will an experience point apply to?
  • What can an experience point be spent on?

Classical class-based systems assume that experience is assigned (or applied) to the whole character and that experience points can only be spent on gaining character levels. The character is rewarded with experience for every encounter she solves and every bit of the story that she completes. This experience applies to her whole character and can be spent on a new character level when the quantity of experience crosses certain thresholds. Every facet of the character advances at once.

Skill-based systems have XP that applies in a smaller scope. XP may apply only to the ability that led to the XP gain, as in Darkfall. XP may be gained by the character as a whole, but only be applied to one ability at once, as in Asheron’s Call. Their may be multiple growth resources that are spent in different ways, as is the case in Final Fantasy Tactics. The hybridization of skill- and class-based systems can yield a lot of variety, though most of the possible systems, as Psychochild would say, suck.

When XP applies to less of the character and can be spent on smaller units of growth, character advancement becomes more continuous.

A Schematic for Character Growth

Based on the discussion above, we can construct a schematic that describes all character growth systems. By defining the following, we can accurately describe the character growth mechanics in a game:

  • A set of abilities, their prerequisites, and their growth costs.
  • A set of effects, their prerequisites, and their growth costs.
  • A set of growth resources.
  • A set of completed actions that grant growth resources and how much of each resource they grant.

All character advancement systems are a combination of a these few basic concepts. Understanding them as such can help us evaluate game mechanics without becoming caught in the rhetorical traps and false distinctions that doom so many discussions to religious warfare and unproductive pontification.


Brian 'Psychochild' Green said...

Great article!

Now go back to your use-based system article and present a critique of why you think that use-based systems are inferior to the alternatives.

Unknown said...

Have you ever played or read the rules for the old pen and paper Runequest game? Not the new version, but the old school one by Avalon Hill?

IMO, it was the best skill based RPG that I ever played. Every skill in the game had a percentage based chance of success, whether that was swinging a sword, shooting a bow, crafting, climbing, etc. Whenever you successfully used a skill during an adventure, you put a check next to it. After a major milestone in the adventure, you would make advancement rolls for all of the abilities with a check. The interesting part was that you had to roll higher than your current ability to advance. Therefore, as you got better, it became more difficult to advance. You ended up with the nice smooth "Optimal Skill vs Time" graph above in a very elegant way.

Since we are talking about computers, and not pen and paper, you can use whatever scale gives the best effect. So, for example, you might still use a percentage based system, but every successful check only gives you an 0.1 or 0.01 percent increase. You could rule that you get a "check mark" every time you land a killing blow or every time you score a critical hit, or something like that. And you test to see if you advance at the end of every combat, or every N combats, or maybe every time that you enter an inn. Basically, you can scale it so that it takes the appropriate amount of time and/or fights to get to maximum level.

Matt said...

It's maddening to compare and contrast various character progression schemes with someone if they don't understand this abstraction. This post will be a nice reference when the topic is inevitably raised in the future.

One thing I would find interesting is a set of graphs showing power vs. time curves for actual games or game elements. Character power may be somewhat difficult to quantify since there are a lot of variables, but something simple such as a specific spell's damage or a character's HP may provide insight into the general shape of a game's curve.

Additionally, it would be interesting to see that compared against the power curve for a particular mob in the same game. For example, does a fireball do the same percentage of damage to a mob's HP at level 1 as it does at level 50? Does character HP increase at the same rate as mob HP or do they diverge/converge?