XTree v1.00

[The Hive Custodian]

XTree
Version 1.00 | 8 October 2007

Created by The Hive Custodian

[The Hive Custodian]

Chapter I: Introduction
Note: Throughout this text, bold is used to indicate section titles, italics are used to introduce terms, and underlining is used to indicate emphasis and some headers. When the text refers to "you", it may mean "your character". "Player" is used to refer to anybody playing a roleplaying game utilizing this system.

XTree is a system for describing the abilities of characters in a roleplaying game. This is the sole purpose for which is designed; it suitability for use or combination with anything else not designed for XTree is purely coincidental. XTree balances characters against each other through the use of a point system. XTree is designed to be minimalist and customizable.

XTree is not intended to be a complete roleplaying game by itself, although it can form part of one. You will need some sort of action resolution system, a setting, and a set of player roles in addition to XTree to make a complete roleplaying game. Other elements beyond these may be helpful as well.

[The Hive Custodian]

Chapter II: Basics
In XTree, stats are used to describe how good or bad you are at different aspects. There are seven rings of stats, ranging from very general to very specialized. These stats are arranged in a tree, such that each stat branches out into a number of more specialized stats. You will have a level in each stat, which is a number describing how good they are at that thing. How levels are assigned will be discussed in the next chapter. All stat names here are examples only; you should create your own stat trees to better fit your game.

A. Stat Types
From most general to most specific, the stat rings are as follows:

Ground (Ring 0): There is only one Ground stat. You are free to name it whatever you wish; in this text it will be called Ground. The important thing is that it covers everything. If you have a high level in Ground, you're good at everything.

Root (Ring 1): Ground branches off into five Root stats. Example: Ground might branch off into Strength, Agility, Intelligence, Personality, and Magic.

Trunk (Ring 2): Each Root stat branches off into two Trunk stats, for a total of 10 Trunk stats. Example: Intelligence might branch off into Perception and Thought.

Limb (Ring 3): Each Tree stat branches off into three Limb stats, for a total of 30 Limb stats. Example: Thought might branch off into Instinct, Reason, and Memory.

Root, Tree, and Limb stats are collectively called inner stats. The complete selection of inner stats is determined before the game starts; in other words, no new inner stats should be created once the game starts. This is the defining feature of inner stats. Try not to have any two inner stats of the same ring overlap.

Branch (Ring 4): Each Limb stat branches out into roughly three Branch stats. A Branch stat might be someone's general vocation. Example: Melee.

Twig (Ring 5): Each Branch stat branches out into roughly three Twig stats. A Twig stat might be a specific vocation or a major in college. Example: Mathematics.

Leaf (Ring 6): Each Twig stat branches out into roughly three Leaf stats. A Leaf stat might be one aspect of a specific vocation, or the subject of a few classes in college. Example: Jazz music.

Limb, Branch, and Twig stats are collectively called outer stats. Anybody can make up a new outer stat at any time; as such, there can be no comprehensive list of outer stats. This is the defining feature of outer stats. Unlike inner stats, you shouldn't get too caught up in trying not to make the outer stats overlap; just make sure each stat is about three times as specific as the stat it branches out from.

Stat Relationships
You can describe the relationship between two stats as if they were members of a family. A parent stat branches out into its children. A stat's parents, its parent's parents, and so on are its ancestors. Its children, its children's children, and so are its descendants.

Anything covered by a stat is also covered by its ancestors. By the same token, a stat covers everything that its descendants cover.

B. Creating A Stat Tree
There is no standard tree of stats. It is up to the players to create a stat tree appropriate for the game. Start with the innermost, most general stats and work down toward the outer, more specialized stats.

Again, inner stats are determined before the game starts. Some guidelines to creating inner stats:
Since the set of inner stats is fixed, care should be taken in their creation.
Make sure each Ground, Root, and Trunk stats each branch out into the correct number of stats.
Make all the branches of a stat roughly equal in usefulness; depending on what kind of game you are playing, some stats may be more or less important. The idea is that nobody should be penalized for investing more in one part of the tree than another.Outer stats can be created by anybody on the fly. It is not so important to make sure they branch out evenly. Overlapping is fine, and if there are any gaps you don't like, make up a new stat to fill it. Simply say what you want, have it branch off from (roughly) appropriate stats, and give it an appropriate type.

Some guidelines to creating outer stats:
You do not need permission from anybody to create new outer stats, but keep it reasonable.
Stats should only cover things that are actually possible in the game. For example, if there is no magic in the game, don't make up a Magic stat.
All outer stats should fit under some inner stat.
The type of a stat can be changed if it is too general or specific for that type. Usually it will not be necessary to ban a stat altogether.A final note: Stats describe characters, not players. If, for some reason, something depends on how good the player is at it, don't make it a stat. On the same note, avoid buying levels you can't roleplay if you can help it.

B. Levels
1. Applying and Combining Stats
In a given situation, how well you perform is determined by any stats you have that are relevant to that situation.

Start with the most specific stat relevant to the situation. If a stat is relevant to a situation, then all of its ancestors are as well because they cover the same things as that stat (and more). Just add all the levels of the most specific stat and its ancestors together to get a total level for that situation. It may be useful to write the total level of each stat and its ancestors next to the level of that stat alone.

Sometimes a situation might depend half on one specific stat and half on another. In this case, each of the stats contributes half of the total levels of itself and its ancestors. A single ancestor can count on both sides if it covers both of the specific stats. Similar things apply to three stats, situations where one stat matters most but another has some importance, etc.

2. Comparing Stats
The advantage one character has over another in a situation is based on the proportion between their levels in relevant stats. A character with 12 levels has a certain advantage over someone with 8; a character with a 21 has the same advantage over someone with 14, since in both cases the first character has 1.5 times the levels. A character with 18 has twice that advantage over a character with 8, since that character has 1.5 times the levels again (8 times 1.5 is 12; 12 times 1.5 again is 18).

3. Scales
A total level of 10 is considered the average for a human without special training. Therefore, a particularly boring human with Ground 10 and nothing else might have 1,000 SPs. Realistically, the average human does have special training in one or more areas and will have more SPs than this, perhaps 1,200 to 1,500. Player characters, of course, might have even more (or less, in a certain kind of game).

[The Hive Custodian]

Chapter III: Characters
This section describes how to create stats for a character using XTree.

A. Stat Points
As stated before, XTree uses levels to describe how good you are at a particular stat. Levels in stats are purchased using Stat Points (SPs). You start with a number of stat points determined before the game begins. Usually all players will start with the same number of SPs. SPs represent your training, experience, natural ability, and any other advantage you might have. For each SP you spend on a stat, you get one level, or some fraction thereof, in that stat. The more specialized the stat, the more levels you can get in it for a given number of SPs (or conversely, the less SPs each level costs). On the other hand, a more specialized stat is not applicable to as many situations.


Stat Levels/ SPs/
Tier SP Level
Ground (0) 0.01 100
Root (1) 0.05 20
Trunk (2) 0.1 10
Limb (3) 0.3 3 1/3
Branch (4) 1 1
Twig (5) 3 1/3
Leaf (6) 10 1/10
It makes sense to buy general stats in large chunks (in terms of SP), and specialized ones in smaller chunks.

You do not have to spend whole SPs. For example, you could spend 0.1 SP on a Leaf stat and get 1 level in it. Please try to keep to round numbers or at least decimals, however; nobody is going to appreciate you having 4.3569 + pi^2 - sqrt(3) * 11/7 levels in a stat.

B. Adding Color
Colors complement stats in describing you. A color is simply a detailed description of a stat that someone could get be looking at your character description. (A reminder in the stats never hurts, though.) You can have as many colors as you want. Some things you can do with traits:

Describe how your stat works. Where did you get your ability in that stat? Is it natural talent, training, magic, or something else?
Describe what areas within this stat you are relatively strong or weak in (for the stat's level). While this could be done explicitly through creating more specific stats, sometimes it may be cumbersome to do so. In all cases, if you are particularly strong in one part of the stat (for its level), you are weak in another area, and vice versa. (No free lunch.)

C. Creating a Stat Sheet
Follow these guidelines when making a character sheet:

1. Check With the Other Players
Before you do anything, check with the other players and figure out what kind of games this is going to be. That way, you don't show up with an incompatible character. What kind of characters should be in this game? What kind of setting is the game in? What is the tone of the game? What's the power level of the characters going to be (in other words, how many SPs are you starting with)?

2. Create a Character
Before you do anything remotely involving making a XTree character sheet, make sure you have your character. Know what you want your character to be good and bad at. Your character is infinitely more important than your character sheet, because you can always create your character sheet from your character, but not as well the other way around.

Also, try to corroborate with the other players when making your character. This will help your character fit in with the other characters and the story much better.

3. Buying Stats
Figure out what you want to be good and bad at, and then spend your SPs accordingly. You'll probably invest a lot of points in Ground (as in, at least a few hundred).

4. Basic Notation
The basic notation for a character sheet is as follows:

Stat Points: [# SPs]

Levels:
Ground [Level]

>[Stat] [Level] ([Total Level])
>>[Stat] [Level] ([Total Level])
[...]

SPs Spent:
Ground: [# SPs spent]

>[Stat]: [# SPs spent]
>>[Stat]: [# SPs spent]
[...]

Traits:
[Traits]

You don't have to include stats that you have no level in. However, it may be useful to include Ground and other stats that lead up to stats that you do have levels in.

Put > signs to help indicate the type of a stat.

D. Character Advancement
If the players wish, some method of awarding SPs to characters as the game progresses can be implemented. However, such methods are beyond the scope of this text.

[The Hive Custodian]

Information
Version History

Version 1.00 (8 October 2007)
First public release.
Section II.B.1,3 rewritten to be clearer.
Some typographical errors fixed.

Version 0.06 (9 April 2007)
Visual stat notation changed.

Version 0.05 (9 March 2007)
Introduction changed.
Added an appendix: Additional Notation.

Version 0.04 (12 February 2007)
"Tier" changed to "ring" to better fit the "inner" and "outer" terminology.
Recommended notation changed.

Version 0.03 (11 January 2007)
Design notes added.
Clarification that non-integer levels are allowed.

Version 0.02 (10 January 2007)
The major divisions of the text are now explicitly called chapters.
Levels section moved to Chapter II: Basics. The intent is to allow for almost of a XTree stat sheet to be understandable after reading only that chapter.
Introduction lengthened.
Appendix added, detailing some possible modifications to the system.

Version 0.01 (3 January 2007)
I have realized that XTree's purpose is not to be a full roleplaying game, but a system for describing characters. As such, the bulk of the material not dealing with such, including chapter IV, has been removed. This way, players can combine XTree with other elements of their choosing to form a complete RPG.
"Traits" changed to "color", which I feel is closer to their function.

Version 0.00 (22 December 2006)
First version of XTree.
XTree is intended as a replacement for TripleTree. Changes include:
Linear scale instead of logarithmic scale; comparisons between stats based on proportion rather than difference.
System is closer to base 10 to aid computations.
General rewording.

Credits
Created by:
The Hive Custodian
Thanks To:
AllTogether Andrews
Doomsmile
nightinverse
Takkaryx
Hosting:
www.online-roleplaying.com (http://www.online-roleplaying.com)

[The Hive Custodian]

Appendix I: Additional Notation
This appendix introduces possible additions to character sheets beyond the basic notation.

Visual Stats
Levels can be represented graphically as well as through numbers. The default method for doing so is as follows:

Use a sheet of gridded paper, or if on a computer, an image (.png is probably the best format). One square on the grid represents 1 level; one pixel on a computer image represents 0.01 level.

For each box or pixel after the first, fill in the next box or pixel until you have a line 10 long.
Then, fill in the next line. Continue filling in lines until you have 10 lines, or a square 10 on each side.
If you have more than 100 boxes or pixels, make 10x10 squares in the same pattern first until you have less than 100. Do the same with 10,000 boxes or pixels and 100x100 squares, and so on.
Include any levels in ancestor stats, using a different color.

[The Hive Custodian]

Appendix II: Modifications
The rules of XTree can be further modified to suit your needs. This appendix describes some of the ways this can be done, in roughly ascending order of how dramatic the changes are. Of course, you are free to make up your own modifications to the system.

Changing Stats
Although this is mentioned earlier, it warrants a mention here. The most basic way to customize XTree is to create a stat tree with the stats you desire.

Changing Number of Branches
You can change the number of ways each stat of a certain ring branches out into. If you do so, be sure to modify the cost table accordingly. For example, if you make each Trunk stat branch out into 5 Limb stats (instead of 3), make sure that Limb stats get 5 times as many levels per SP (instead of 3 times as much). Notice this may affect stats that are further out as well.

Changing Number of Rings
You can change the number of stat rings, and also the number of rings that are outer and inner stats.

Negative Levels
You can allow negative levels for inner stats, so long as no character buys so many negative levels that there is some situation in which they could have a non-positive total level. Allowing negative levels like this will not affect any outcomes; it will simply allow for more ways of representing the same thing.

Overlapping Branches
Instead of having each stat branch out into a single set of stats, you could have stats of some rings branch out into multiple sets of stats, which represent different ways of splitting up the aspects of a character. A character's total level would depend on all relevant stats.

[The Hive Custodian]

Appendix III: Design Notes
While not necessary for the playing of XTree, I have included these design notes in the hopes that they will offer some insight into why certain things in XTree are the way they are.

History
XTree is the latest system based on this tree idea. This project began in June of 2006. Originally, it was just called Tree. For most of the time here on Online-Roleplaying, it has been called TripleTree, because it was based on 3 (each stat branched off into 3 stats). TripleTree used a logarithmic level scale, which means (in its case) that each level cost three times as much as the one three levels ago, and stat comparisons were based on the difference between the stats, rather than the proportion.

Later, I realized that a system based on 3 and logarithmic scales isn't very easy for the average player to understand, so I switched over to a linear scale and brought things closer to being 10-based, hence the X.

Purpose
XTree is essentially an attempt to boil the stat concept to as simple a form as possible while retaining enough structure to keep things coherent.

Some of the goals I had in mind when designing XTree:

Simplicity. Simplicity was one of my greatest considerations in designing XTree. (Unfortnately, what is simple to me may be complicated to someone else, and vice versa. For example, I believe I dislike large tables more than the average person.) I tried to make XTree as short and simple as possible while retaining its structure.

Connection between roleplaying and stats. XTree's primary purpose is as a system of representing characters; it is not designed to fit a particular rules system. It may be possible to design a good rules system around XTree, although any such system should follow the guidelines for comparing stats. I tried to make the mechanically optimal choice in XTree coincide with the best roleplaying choice. Consider this admittedly simple (yet one that warrants a lengthy explanantions) model of power:

First, consider the advantage one character has over another in a particular stat. To take the example from the text, a character with 12 levels in a stat has a certain advantage over someone with an 8 in that stat; a character with a 21 in a stat has the same advantage over someone with a 14, since in both cases the first character has 1.5 times the levels.

Now, let us extend this idea. Suppose a character has 1.5 times the levels again (for a total of 1.5 times 1.5, or 2.25, times the levels). Would it not then be reasonable to say that such a character has twice the advantage?

This idea is embodied in the logarithm function. Picking an arbitrary reference point, we can express the advantage given by a certain level as a ln level, where a is some constant that accounts for the base of the logarithm; essentially how the advantages are scaled.

Also notice that any set of stats and levels can be changed around so that only stats of the outermost ring are used without changing any total level (barring outer stat wierdness).

Now we make a critical assumption: the power of a character is equal to the sum of the advantages in all the character's stats (after converting all stats into the same ring), weighted by a constant that describes how important that stat is to that particular character. A character's power is then a * sum over all stats (b_n ln level_n), where b_n is the weighting constant of the nth stat, and level_n is the level of the n_th stat.

Consider the case of a two-stat system. Any points not spent on the first stat are spent on the second, so the power function becomes a ((b_1 ln (p q) + b_2 ln ((1 - p)q) ), where p is the proportion of points spent on the first stat and q is the total number of points. We can optimize this by taking the derivative with respect to p and looking for the zero. The derivative comes out to a * (b_1 / p - b_2 / (1 - p)). Equating this to zero, we have

a (b_1 / p - b_2 / (1 - p)) = 0
b_1 / p - b_2 / (1 - p) = 0
b_1 / p = b_2 / (1 - p)
b_1 / b_2 = p / (1 - p)

Consider the meaning of this: The optimal proportion of points depends only on the importance of the stats. In particular, it does not depend on the base of the logarithm, nor does it depend on the total number of points. Furthermore, this optimal proportion is exactly the same as the proportion of the stats' importance.

Now we rewrite our original equation. Suppose q points are given for us to spend. Normalizing a, we have

((b_1 ln (b_1 q / (b_1 + b_2)) + b_2 ln (b_2 q / (b_1 + b_2))
= (b_1 + b_2) ln q + a constant

Since constants don't matter for optimization, this is effectively equivalent to (b_1 + b_2) ln q. Thus, these two stats can then be considered a single stat whose importance is the sum of the importances of the two stats. By induction (repeating the same argument with this bundled stat and a third stat), we find that the optimal distribution of points into an arbitrary number of stats is also proprortional to the importance of those stats.

Flexibility. I wanted XTree to be a general system of sorts; in this respect, perhaps it is better termed a "meta-system", as XTree is not so much a system as a template for configuring your own system. To this end, I tried to keep the number of unique mechanics to a minimum. In this case, there are only stats and color.

Specific Elements

Why a tree? A tree seemed to be the easiest system for organizing stats. In theory, one could imagine a system like XTree but with only a single ring of stats. On the plus side, you wouldn't have to deal with different stats giving different amounts of levels per SP. However, there are a few major problems with such a system. First of all, how specific do you make the stats? If you make them too general, you lose out on detail. If you make them too specific, you end up with far too many stats to keep track of--especially in a system where specialized stats can be created on the fly. Second, consider this situation: suppose someone comes up with a Ping-Pong stat. Obviously nobody has invested in it, since the stat didn't exist before. But would it really be right to suppose that everyone else has no ability in ping-pong whatsoever?

At another extreme, consider the tree idea taken to its most general form, where it no longer resembles a tree; stats can be created on the fly with no restrictions, and a levels per SP value is assigned to each stat based on how specific it is. This allows for a lot of freedom--but how would one figure out how many levels per SP to assign to each stat? It would be impossible to create guidelines for the infinite different stats that people could come up with, if they were allowed to do so without any restrictions in place.

Using a tree solves these issues. By paying some cost in redundancy (buying levels in Ground accompishes exactly the same thing as buying equal numbers of levels in all Limb stats, for example) and freedom (stats have to fall within rings), XTree strikes a balance between structure and freedom.

Why inner and outer stats? I suppose if one wished to, they could do away with the concept of inner stats entirely, and allow all stats to be made up on the fly. However, I included inner stats for many of the same reasons above. Having inner stats provides something of a "common language" between characters.

Why no prerequisite mechanics? I wanted to create a character creation system in which your options do not depend on the past state of your character. This is for a few reasons. First, I find it an irritating feature of many roleplaying games that one cannot go back and change aspects of a character's stats once stat-building decisions are made. People change over time, after all, and furthermore the character you build the first time may not be the character you really wanted. It is difficult to make prerequisite mechanics compatible with a system that does allow retroactive changes. Second, prerequisite mechanics lengthen the time needed to create a character's stats, since one needs to worry about the character's stat history and not just the character's current stats.

Continuous versus discrete. Most roleplaying systems that I have seen rate stats at discrete levels: 1, 2, 3, 4, and so on. XTree, on the other hand, allows a nearly continuous spectrum of levels. This is in accordance with its focus on representing characters versus supporting a rules system, as it tends to be easier to build a rules system for discrete levels, at least for tabletop systems.

Another example of discrete-ness is that of abilities. XTree is not well-suited to discrete abilities such as the specific spells found in many games. Instead, it is much better at handling a more general ability, such as general control of fire magic or the like.

[The Hive Custodian]

Still rough, obviously, but you can see the major changes. I think it might be shorter than my character questionnaire...

[The Hive Custodian]

Updated to v0.01.

[The Hive Custodian]

Updated to v0.02.

[The Hive Custodian]

Updated to v0.03. I've added design notes.

[The Hive Custodian]

Updated to 0.05. I've added a visual way of representing stats, which should make it easier to compare stats.

[The Hive Custodian]

Updated to 0.06.

[The Hive Custodian]

First public release! At this point, I think I have made nearly all of the mechanical changes that I will ever make to this system. Originally I had planned to run a test game before releasing this publicly, but unfortunately I have not had time to do so and will not in the foreseeable future, which is why I am releasing it now. Hopefully at least a few of you will get some use out of this. If I ever do get a test game together, I'll be sure to post about it.

A few related threads:

TripleTree, a precursor project. v0.12 v0.09
Stat tree from an indefinitely delayed test game.

[LeeCHeSSS]

I'm confused, is it downloadable?

[The Hive Custodian]

The first nine posts contain the entirety of the text (i.e, the whole thing is in the thread itself), with replies 2 and 3 containing the core information.

[LeeCHeSSS]

Ahh, so no executable program, but a ruleset!

[The Hive Custodian]

Yeah, sorry about the confusion caused by putting it in software-versioning-like terms.