According to Bill Moggridge in Designing Interactions, the hierarchy of complexity of design constraints consists of six disciplines that designers must navigate as products and systems become more complex:

1. Anthropometrics: Focuses on the physical dimensions and sizes of people.
2. Physiology: Focuses on how the human body works and its mechanical functions.
3. Cognitive Psychology: Focuses on how the mind works and processes information.
4. Sociology: Focuses on how people relate to and interact with one another.
5. Cultural Anthropology: Focuses on the human condition, cultural variations, and societal contexts.
6. Ecology: Focuses on the environmental impact and interdependence of all living things.

As a design problem moves from simple physical interactions to complex, systemic service ecosystems, the constraints increase in complexity, requiring collaboration with specialists from these respective fields.