Blocks of associated traits are used within OpenD6 to describe individual statistical units. A statistical unit is defined as a given block of traits, and includes elements such as characters, vehicles, traps, buildings, equipment, and effects. Traits within OpenD6 are described as occupying one of several tiers.
Tier One traits tend to be broadly defined, and independent of other traits. Multiple Tier One traits may describe a given statistical unit, and may have non-exclusive or overlapping definitions. Attributes are Tier One traits.
Tier Two traits are always associated with a Tier One trait, and are defined within the scope of the Tier One trait’s definition. Multiple Tier Two traits exist within the scope of a Tier One trait, and should be defined as exclusive of other Tier Two traits within the same Tier One trait. Skills are Tier Two traits.
Tier Three traits are always associated with a Tier Two trait, and are defined within the scope of the Tier Two trait’s definition. Multiple Tier Three traits exist within the scope of a Tier Two trait, and should be defined as exclusive of other Tier Three traits within the same Tier Two trait. Specializations are Tier Three traits.
Tier Four traits are sometimes associated with a combination of Tier One, Two, or Three traits, and are sometimes independent of other traits. Tier Four traits are narrowly defined, and may have non-exclusive or overlapping definitions. Options, Move, Body Points, Strength Damage, Funds, Character Points, and Fate Points are all Tier Four traits.
The four tiers of traits interact with each other to form an interdependent block of numbers describing a given statistical unit.