This case-sensitive code system http://hl7.org/fhir/goal-relationship-type defines the following codes:
Code
Display
Definition
predecessor
Predecessor
Indicates that the target goal is one which must be met before striving for the current goal
successor
Successor
Indicates that the target goal is a desired objective once the current goal is met
replacement
Replacement
Indicates that this goal has been replaced by the target goal
milestone
Milestone
Indicates that the target goal is considered to be a "piece" of attaining this goal.
other
Other
Indicates that the relationship is not covered by one of the pre-defined codes. (An extension may convey more information about the meaning of the relationship.)