User: access content preference, topic preference, friends, preference of friends, click history, access history, comment, thumb up, thumb down
create user profile, generalize and represent as vector -> embedding
user interest shift, collect history may change in future and become a withdraw
predict user interest shift -> time series, time decay
some user interest is ad hoc, sometimes they look at some content and search for it.
some interest is long term
find out what interest is ad hoc and what is long term
