  Dialogue system (DS) attracts great attention from industry and academia
because of its wide application prospects. Researchers usually divide the DS
according to the function. However, many conversations require the DS to switch
between different functions. For example, movie discussion can change from
chit-chat to QA, the conversational recommendation can transform from chit-chat
to recommendation, etc. Therefore, classification according to functions may
not be enough to help us appreciate the current development trend. We classify
the DS based on background knowledge. Specifically, study the latest DS based
on the unstructured document(s). We define Document Grounded Dialogue System
(DGDS) as the DS that the dialogues are centering on the given document(s). The
DGDS can be used in scenarios such as talking over merchandise against product
Manual, commenting on news reports, etc. We believe that extracting
unstructured document(s) information is the future trend of the DS because a
great amount of human knowledge lies in these document(s). The research of the
DGDS not only possesses a broad application prospect but also facilitates AI to
better understand human knowledge and natural language. We analyze the
classification, architecture, datasets, models, and future development trends
of the DGDS, hoping to help researchers in this field.
