What is an Opinion? (Liu, Ch. in NLP handbook)
An opinion is a quintuple
(oj, fjk, soijkl, hi, tl),
oj is a target object.
fjk is a feature of the object oj.
soijkl is the sentiment value of the opinion of the opinion holder hi on feature fjk of object oj at time tl. soijkl is +ve, -ve, or neu, or a more granular rating.
hi is an opinion holder.
tl is the time when the opinion is expressed.