classDiagram
class Difficulty {
}
class OpenQuestion {
}
class UndesirableCondition {
}
class Problem {
}
class Investigation {
}
class Consideration {
}
class Solution {
}
Difficulty --|> Problem : is
OpenQuestion --|> Problem : is
UndesirableCondition --|> Problem : is
Problem --> Investigation : needs
Problem --> Consideration : needs
Problem --> Solution : needs
A difficulty, open question or undesirable condition that needs investigation, consideration, or solution.