As computers are getting bigger better and faster, the concept of what constitutes a single datum is changing.
For example, in the world of pen-and-paper, we might take readings of temperature over time and obtain a time-series in which an individual datum is a time, temperature pair. However, it is now common to desire classifications of entire time-series, in the context of which our entire temperature time-series would be but a single data point in a data set consisting of a great number of separate time-series. In image processing, an $(x,y,c)$ triple is not a datum, but a whole grid of such values is a single datum. With lidar data and all manner of other fields things that were previously considered a dataset are now best thought of as a datum.
What is the term for datasets that are themselves composed of datasets?
The term "metadata" is occupied, I should think.
Are there any papers that talk about this transition from datasets of data to datasets of datasets? And what the implications are for data scientists and researchers?