Describing objectives

Action-selection systems often have some mechanism for directing them to accomplish specific objectives.  The most common of these are:

• Goals
  A goal is some partial state that the system should try to achieve. For example, being in a particular location, possessing a particular item, or some other character being dead. The goal says "put me in some state where this is true."  Goals are often divided into:
  • Achievement goals are to get into some partial state.  Once you get into it, you're done.  All the examples above are achievement goals.
  • Maintenance goals are to stay in some partial state you're already in.  “Stay alive” is a maintenance goal.
  • Avoidance goals are to stay out of some partial state.  “Don't starve” is an avoidance goal. Avoidance goals a special case of maintenance goal: avoiding something is the goal of maintaining its opposite.
• Tasks
  A task is some activity to perform, such as having dinner with someone.  Tasks are easy to confuse with goals.  Getting married, in the sense of going through the marriage ceremony, is a task in this sense of an activity to perform.  Being married, on the other hand, is a goal because it's a partial state the character should be in at the end.
• Utilities
  Utilities are a kind of implicit specification of an objective.  Many systems that use utilities just have one objective: maximize utility. The designer specifies the object implicitly by adjusting how utilities are calculated.