Revisit the data structures used to represent a cohort about cool HOT 3 CLOSED

Actually, the new cohort processing engine can't support process query based on input cohort result currently.
Maybe we should discuss how to implement it and set a reasonable standard according to the modification in global id in next meeting.

from cool.

Update: the cohort will be persisted in a new format that stores the result cublet-wise, since all processing are done cublet by cublet. cublet level id for the user key will be used in this format.

Regarding the dataset update, it will not be addressed with the cohort representation. Each cohort is tied to a certain version of a cube. Hence, the problem shall be addressed by processing to consume a cohort of old version and the actual data to identify the diff with the new version and generate a new cohort (updated cohort).

from cool.

Update: we finally decide to use Strings of user names to store the cohorts. When loading the cohorts, we transfer the strings into global ids which may be different in diverse cublets.
Fixed in PR #105

from cool.