Semantic validation becomes a side-effect
Computing an emergent property value often isn't possible without validating the interchanged information on which the computation is based.
- For example, if an element that inherits from a vocabulary specifies a "start-time" attribute and an "end-time" attribute, we may intend that the duration of time between the start-time and the end-time be calculable and that it fall within a certain range (or at least be non-negative). In any case, we can't calculate the value of the "duration" property unless the start-time and end-time values exist and are amenable to calculation.