The Skotos Bulk System Models of a Physical World All multiplayer interactive fiction games model the physical world in simplified ways. These models prohibit character actions that should not be possible. Without such prohibitions players' suspension of disbelief would be broken. Most of these systems have a model for bulk. These models might have a variety of results from limiting item storage (i.e., limiting character inventory) to modifying character abilities (i.e., reducing stamina). Some systems also model dimensionality, allowing objects to have a size. These models determine whether items can fit in containers (or rooms) or describe the size of items relative to one another. Approaches Many multiplayer interactive fiction systems take a minimalist approach to modeling the physical world. In the simplest model of bulk, items are given a mass and containers are given a maximum mass. This is easy for players to understand. However, differing densities cause paradoxes such as a feather pillow taking up the same amount of space in a container as a gold coin. Most systems extend this model to give items a bulk and containers a maximum bulk. Again, this is easy for players to understand. It also doesn't require much extra work by the world builder. However inconsistencies still crop up that undercut the realism of the simulated world. A few systems have drastically increased the number of physical attributes of an item. This results in more realistic physics but also produces a very complex model. World builders must put more effort into each item. Inconsistencies and errors are common. Problems Solved by the Skotos Bulk System A chatroom wouldn't require a complex bulk system. However in a fully featured game players will inevitably encounter complex situations involving bulk. The Skotos Bulk System models tricky situations such as: Large winged dragons trying to get into houses. The dragon would not fit through a small door (without destroying it and, possibly, the house). Multiple swords being shoved into a scabbard. A scabbard would be designed to fit a specific variety and size of sword. And, a player could stuff a scabbard with cotton in order to fit a smaller weapon like a dirk (or a banana). Objects being pushed through small holes. A rope could be fed through a small hole into a large cave. Sadly an elephant would not fit through the same hole. People of different size contesting for seating room. A particular oak bench might be able to seat two ogres, four humans, or six dwarves. Summary of the Skotos Bulk System The Skotos Bulk System is built on ten attributes based on physical values and one attribute which is used for relative dimensionality. Three of the physical values are calculated. The three basic physical values are: Mass ( kilograms [kg] ) Density ( 1000 * kg/m^3 ) Longest Dimension ( meters [m] ) Four additional values are used primarily for containers: Capacity ( cubic meters [m^3]) Max Weight ( kilograms [kg]) Max Depth ( meters [m]) Max Entrance Area ( square meters [m^2]) The three derived physical values are: Minimum Volume ( cubic meters [m^3]) Actual Volume ( cubic meters [m^3]) Minimum Frontal Area ( square meters [m^2]) It should be noted that the derived values can produce approximations that aren't quite correct. The idea is to arrive at a good compromise between data entry and realism. In addition there is one special purpose attribute: Relative Size ( percentage ) Basic Attributes Mass Unit: kilograms [kg] Mass measures the amount of matter in an object. It's the simplest physical measurement. A huge iron kettle will have a mass of 30 kg. A wooden staff would have a mass of 1 kg. Density Unit: 1000 * kg/m^3 Density affects the compactness of an object. World builders choose density from a list of materials. The densities of some common materials are: Wood 0.7 Water 1.0 Iron 7.8 The iron kettle has a density of 7.8. The wooden staff has a density of 0.7. A commonly used alternative to density is _specific gravity_, the dimensionless ratio of an object's density to that of water. Thanks to of our choice of units, where one cubic meter of water weighs 1000 kg, density and specific gravity are equal in value. Longest Dimension Unit: meters [m] Longest Dimension is the greatest of the object's x, y, and z dimensions. The cauldron is a hemisphere with a 0.5 meter radius. Its longest dimension is its width (or diameter); 1 meter. The wooden staff has a longest dimension of 2 meters (its length). Basic Container Attributes Capacity Unit: cubic meters Capacity is the total volume an item can hold or carry; containers are the object which most often use this value. A non-container may list capacity to denote "dead space" inside an object. Capacity limits the Actual Volume that may be put in a container. The huge iron cauldron has a capacity of 0.26 cubic meters. (This figure was actually derived because of our understanding of the cauldron's shape. The volume of a sphere = 4/3 * pi * r^3 = 4/3 * 3.14 * .125 = .52. The cauldron is only half a sphere, so the capacity is determined to be .26 cubic meters. Other calculations, guesses or real examples would be required for other types of objects.) The wooden staff has a capacity of 0. Max Weight Unit: kilograms [kg] Maximum weight is how much a container can hold until it bursts, rips, cracks, or whatever. (The Skotos system currently assumes common sense and will stop all attempts to overflow a container.) Max Weight limits the Mass that may be put in a container. The huge iron kettle could hold a great deal of weight (500 kg). The wooden staff can hold nothing (0 kg). Max Depth Unit: meters [m] The maximum depth measures how big of an item can fit inside of a container. Max Depth limits the Longest Dimension of what may be put in a container. The huge iron kettle would have a max depth the same as its height, .5 meter. The wooden staff has 0 max depth. Max Entrance Area Unit: square meters [m^2] Usually this value defines the opening of a bag or chest, but it also works when describing sizes of doors or openings to other areas. Max entrance area is actually an attribute of a detail which belongs to an object. This makes it simple to model an object with multiple entrance: there are multiple entrance details, each with max entrance area defined. Max Entrance Area limits the Minimum Frontal Area of what may be put in a container. The iron cauldron has a circular entrance with a diameter of 1 meter. The max entrance area is thus equal to area of the circle, which is = pi * r^2 = 3.14 * .5^2 = 3.14 * .25 = .79 square meters. We could compute this figure precisely because we knew the cauldron's shape; other objects would vary. The wooden staff is not a container and has no entrances. Derived Attributes Minimum Volume Unit: cubic meters [m^3] Calculation: mass in kg / (1000 * density) This value is the volume of the item in its most compressed form. The minimum volume of a huge iron kettle = 30 kg / (1000 * 7.8) = 30 kg / 7800 = .00385 cubic meters. The minimum volume of a wooden staff = 1 kg / (1000 * 0.7) = 1 kg / 700 = .00143 cubic meters. Actual Volume Unit: cubic meters [m^3] Calculation: capacity in cubic meters + minimum volume in cubic meters This values define the normal volume when the object is not in its most compressed form. The actual volume of the huge iron kettle = .26 m^3 + .00385 m^3 = .264 m^3. The actual volume of the wooden staff = 0 m^3 + .00143 m^3 = .00143 m^3. Minimum Frontal Area Unit: square meters [m^2] Calculation: actual volume in cubic meters / longest dimension in meters Minimum Frontal Area is more commonly known as the smallest face of the item. It helps define what an object can fit into. The smallest face of a huge iron kettle = .264 m^3 / 1 m = .264 m^2. The smallest face of a wooden staff = .00143 m^3 / 2 m = .00072 m^2. Other Attributes Relative Size Unit: percentage of "expected" size This is the scale of an object. A relative size of 100(%) means that the object is average size when compared to the expectations of a normal, knowledgeable human. Thus relative size is independent of actual bulk: a ring, a chair, and a bed could each be relative size 100(%) if each was normal human size. The relative size system, being subjective and perceptual, is not directly derived from any of the objective attributes. If the relative size of an object is 0(%), then it is assumed that the average human has no ability to measure the scale of the object. Some new or unusual objects might be given a relative size of 0(%) until they become common enough for characters to compare them, at which time they would get actual size values. For more information on Relative Size, see "Relative Size - Technical Concept" The .5 meter tall cauldron is a little shorter than most cauldrons. Its relative size is 90%. The 2 meter tall staff is about normal human size. Its relative size is 100%. Estimating Physical Attributes The Skotos Bulk System offers a good compromise between data entry and realism. However Skotos StoryBuilders may want to option to enter even fewer values. This might be particularly important if the StoryBuilder doesn't have particularly good ideas about all of the physical values. The Skotos Bulk System accommodates this: A few values are absolutely required. The Skotos Bulk System will guess other values. The Skotos Bulk System permanently stores the knowledge of which values are guessed and which have been entered. Entering the Required Values Two of the three basic physical values must be entered for the Skotos Bulk System to guess the others. Density is required. The StoryBuilder will be able to choose from a list of materials. The StoryBuilder must also enter either Mass or Longest Dimension. The StoryBuilder must also declare whether an object is a container or not. After the StoryBuilder has entered these values, The Skotos Bulk System can guess everything else. Guessing the Other Values In order to estimate physical attributes of an object based on limited information the Skotos Bulk System has to make some crude approximations. For a non-container the Skotos Bulk System approximates the object as a square. If density and longest dimension have been supplied and the object</tt> is not a container: capacity = 0 max weight = 0 max depth = 0 max entrance area = 0 minimum volume = longest dimension^3 mass = minimum volume * 1000 * density actual volume = capacity + minimum volume minimum frontal area = actual volume / longest dimension relative size = 100 If density and mass have been supplied and the object is not a container: capacity = 0 max weight = 0 max depth = 0 max entrance area = 0 minimum volume = mass / 1000 * density actual volume = capacity + minimum volume longest dimension = cube root of actual volume minimum front area = actual volume / longest dimension relative size = 100 For a container the Skotos Bulk System has to guess how much of the actual volume is the minimum volume (i.e., the volume of the container material) and how much of the actual volume is the capacity (i.e., the volume of space inside the container material). It is presumed that capacity is typically 90% of the actual volume. In addition it is estimated that there is one entrance and it takes up all of one side of the cube. If density and longest dimension have been supplied and the object is a container: max weight = based on the material given in density max depth = longest dimension max entrance area = longest dimension^2 actual volume = longest dimension^3 minimum volume = .1 * actual volume capacity = actual volume - minimum volume mass = minimum volume * 1000 * density minimum frontal area = actual volume / longest dimension relative size = 100 If density and mass have been supplied and the object is a container: max weight = based on the material given in density minimum volume = mass / (1000 * density) actual volume = minimum volume * 10 capacity = actual volume - minimum volume longest dimension = cube root of actual volume max depth = longest dimension max entrance area = longest dimension^2 minimum frontal area = actual volume / longest dimension relative size = 100 Labeling the Estimated Values ManyStoryBuilderwill look at the estimated values and then enter their own values. The Skotos Bulk System includes features to make this simple: All estimated values are clearly labeled as such. Whenever a new value is entered by hand, all of the estimated values are recalculated, as appropriate. State of Development Development on the basic logic of the bulk system is nearly complete. The developer interface functionality is currently at a proof-of-concept level. Attributes such as strength and tentacle length will determine how individual characters relate to the bulk system; these checks will need to be implemented on a per game basis. Open Issues Maximum depth defines the longest dimension of an item that can be fully inside a container. However there are many cases where it is acceptable for an item to not be fully in its container. Swords are not totally inside scabbards. Pencils do not go all the way into pencil sharpeners. Liquids, gases, and squishy or foldable items are not yet modeled by this system. The addition of some boolean values could possibly remedy this. When you pick something up, should we give some additional info about it such as: "It's heavy," "It's unwieldy," "It flops around," etc.? How about throwing in the "Touch" info automatically for the object? In particular games, we will want to display non-metric units. Entering additional information such as the rough shape of an object could allow for better estimations. This might be worth doing at some point. Exactly how to recalculate the estimated values when one new value is entered by hand is not clear. An algorithm tree to allow for every possibility would be complex. Currently, as many of the formulas as possible are written in a way that they will automatically recalculate correctly.