UK National Public Health Language (NPHL) NPHL top-level classes initial ontology, in an iterative design process that continues through the whole of the ontology's lifecycle. 84 This iterative development style is a good fit for complex or wicked problems. Because public health is complex it is technically conceptualised as a 'wicked problem' 85 , meaning that there is no definitive formulation or solution, no 'right' or 'wrong', no absolute truth or perfect solution that holds for all cases-the best that can be achieved is a consensus of public health experts that it is good enough.