The goal of sentiment analysis is to find out whether the opinions expressed in a piece of text are positive, negative, or neutral, especially with regards to s particular topic, product, or company.

Depending on the service, sentiment is typically either expressed as a numeric value between -1 (negative) and +1 (positive), or as a probability for each negative, positive or neutral sentiment class.

In addition, some services provide a sentiment magnitude to indicate how strong the writer’s expressed sentiment is.

Sentiment can be calculated both for each sentence or for a whole text document.