  Product question answering (PQA), aiming to automatically provide instant
responses to customer's questions in E-Commerce platforms, has drawn increasing
attention in recent years. Compared with typical QA problems, PQA exhibits
unique challenges such as the subjectivity and reliability of user-generated
contents in E-commerce platforms. Therefore, various problem settings and novel
methods have been proposed to capture these special characteristics. In this
paper, we aim to systematically review existing research efforts on PQA.
Specifically, we categorize PQA studies into four problem settings in terms of
the form of provided answers. We analyze the pros and cons, as well as present
existing datasets and evaluation protocols for each setting. We further
summarize the most significant challenges that characterize PQA from general QA
applications and discuss their corresponding solutions. Finally, we conclude
this paper by providing the prospect on several future directions.
