Core Mechanics - Fundamentals of Game Design - page 301

This chapter doesn't discuss symbolic relationships much further because they are
relatively easy to define and their results are easier to predict; numeric relationships
are harder to create and tune. Although it is possible to create extremely compli-
cated symbolic relationships (think about Rubik's Cube), most of the symbolic
relationships in games tend to be rather simple.
INTEGRATING SYMBOLIC AND NUMERIC RELATIONSHIPS
Although you cannot perform arithmetic operations on symbolic values, you can
define how symbolic entities change from state to state in terms of other numeric
data. If the symbolic entity fuel warning can take the values on and off , you can
define a mechanic for each of the states based on the quantity of fuel available:
“When the amount of fuel goes below 2 gallons, the fuel warning value switches to
on . When the amount of fuel rises to 2 gallons or more, the fuel warning value
switches to off .”
A symbolic entity can contribute to a mathematical function if you have a
mechanic that associates a symbolic entity into number. For example, the state of
a car's transmission is symbolic; the transmission is either in one gear or another,
and you can't add gears together. But you can make a table that shows the gear ratio
of each gear, and use the results to make computations about the speed of the
driveshafts. For example you can specify, “In first gear, the ratio is 3.83 to 1. In sec-
ond gear, the ratio is 2.01 to 1. In third gear, the ratio is 1.46 to 1. In reverse gear,
the ratio is 4 to -1. The negative value causes the driveshaft to turn backwards.”
This mechanic converts a symbolic entity (transmission state) into a numeric entity
(gear ratio).
The Internal Economy
An economy is a system in which resources and entities are produced, consumed,
and exchanged in quantifiable amounts. Most games have an internal economy,
though the complexity and importance of the internal economy varies consider-
ably from genre to genre. Chapter 18, “Construction and Management Simulations,”
provides more discussion of internal economies.
A game designer spends part of her time designing and tuning her game's econ-
omy, and the more complex the economy, the more time she needs to spend. This
section introduces aspects of an internal economy, which it explains by reference
to both a simple action game (a shooter) and a complex game (a construction and
management simulation).