What granularity to choose for dataset DOIs ?

There is no definitive answer to that question; it is a choice that will depend on data and their usage by scientists. The DOIs main objective is to facilitate and improve the reliability of data citation in scientific publications: a strategy should be defined based on the level of aggregation of data that are generally used in a publication.

If a DOI is assigned at a measurement level and if the related publication manages thousands of these measurements, it will be difficult to cite properly the thousand associated DOIs. In that case, DOIs are probably not properly assigned.

It is likely that for scientific publications exploiting different levels of the same bunch of data, DOIs should be assigned at these specific distinct levels. In the Landing Page of such a DOI it is possible to provide links between the different DOIs so that the reader will navigate from one level to another.