In object-oriented and methodological terminology, PARENT designates the object from which the current object inherits all key properties. You must include RELATE BY “is keyed by” in the statement: see RELATE (BY), RELATED (BY).
Example
DEFINITION "Use Case Step" { PROPERTY "Use Case Name" { KEY EDIT OneOf "Use Case" PARENT RELATE BY "is keyed by" READONLY HELP "Name of Owning Use Case" } ... }