Knowledge
Sentiment analysis
Sentiment analysis automatically assigns a statement a polarity — positive, negative or neutral — without establishing what the statement is about.
Where it comes from
It is the oldest and most frequently sold form of review analysis. It produces a mood chart over time and a percentage of positive reviews. The trouble is that "nice room, but we waited forty minutes" is positive and negative at once, and its aggregate polarity carries no information.
What it means in practice
Sentiment alone leads to no decision. What is useful is a pair: category plus polarity, computed separately for each topic raised in a review. Then instead of "62% positive" you get "waiting at reception: 41 complaints across 218 reviews with text" — a sentence a task follows from.