  Opinion mining refers to the use of natural language processing, text
analysis and computational linguistics to identify and extract subjective
information in textual material. Opinion mining, also known as sentiment
analysis, has received a lot of attention in recent times, as it provides a
number of tools to analyse the public opinion on a number of different topics.
Comparative opinion mining is a subfield of opinion mining that deals with
identifying and extracting information that is expressed in a comparative form
(e.g.~"paper X is better than the Y"). Comparative opinion mining plays a very
important role when ones tries to evaluate something, as it provides a
reference point for the comparison. This paper provides a review of the area of
comparative opinion mining. It is the first review that cover specifically this
topic as all previous reviews dealt mostly with general opinion mining. This
survey covers comparative opinion mining from two different angles. One from
perspective of techniques and the other from perspective of comparative opinion
elements. It also incorporates preprocessing tools as well as dataset that were
used by the past researchers that can be useful to the future researchers in
the field of comparative opinion mining.
