recommendation was obtained from a correct task
type. An example of case (1) is that a subscribed
channel video was added to the related video display
because it was classified as a repeat task during the
lookup task. In case (2), even if the task type was
correctly classified, the video added by
recommendation did not satisfy the user's intention.
This problem was related to the recommendation
evaluation method. Although qualitative evaluations
could be obtained through questionnaires and
interviews, quantitative evaluations of recommended
videos could not be performed; this is because we
could not implement a system that would lead to
quantitative evaluation by, e.g., analyzing videos in
the viewing history.
To evaluate the recommendation result, a
quantitative evaluation of recommended videos
should be performed. At present, we simply add
videos that have been categorically searched, and add
videos from subscribed channels. It is necessary to
consider what kind of recommendation is preferable
in consideration of the results obtained by the
quantitative evaluation.
Since the task type is determined in the first search
session and the recommendation is continued based
on the task type after that, inappropriate
recommendation is continuously made in the case of
an incorrect classification. It is necessary to consider
a system that redetermines the task after watching the
video several times. Then, even if the user’s purpose
in mind changes, it will be possible to continue to
adapt to it dynamically by periodically redetermining
the task type.
In recent years, research on neural networks for
recommendation systems has progressed. YouTube
also incorporates the context of user information such
as video viewing histories and search histories into a
neural network and uses it for recommendation
(Covington et al., 2016). In this paper, instead of such
a large amount of data, we focused on the user's
behavior, which may be based on the user's purpose.
At this time, an important problem is how the user's
purpose and the user's behavior are linked in the video
search. The high readability of the decision tree makes
it easier for us to understand this problem, which will
be difficult when a neural network is used instead.
Bhabad et al. (2017) realized the recommendation
of video related information by ASR and OCR. The
method recommended web links, image links, and
YouTube links based on the text data from images
and sounds cut out from the video. Based on the task
type of this paper, Bhabad’s method worked
effectively when the purpose was clearly defined such
as lookup tasks. On the other hand, it was not suitable
when the users wanted to search a wide range of
videos such as exploration tasks and repeat tasks.
Silva et al. (2017) showed that comments on videos
could devide into technical, or instructional videos,
and non-technical videos. Although this is similar to
our research background, the point of view is
defferent. Since Silva’s method focuses on the video
itself, there are problems with videos increasing every
day and videos with only few comments. By contrast,
since our method focuses on the user’s behavior, it is
possible to avoid problems caused by the video itself.
C4.5, which was used in the decision tree
generation algorithm, has the problem that the
decision tree cannot be updated sequentially.
Especially when the dataset and the user's behavior
are extremely different as in the experiment in this
study, an inappropriate decision is made. Supervised
learning such as C4.5 requires input and correct
answer data and given tasks, and such data cannot be
analyzed sequentially by a decision tree generation
algorithm. It will be necessary to consider measures
that can be updated sequentially, such as
implementing the decision tree generation algorithm
itself in the application.
We adopted query length, scroll depth, and
reading time as behavioral characteristics because
they were general behaviors in search systems. In
addition to these, YouTube has other characteristic
operations such as video preview and maximization
and minimization of the video player. It is necessary
to verify whether these actions and other actions that
are effective in document retrieval are also effective
in video search.
Although we attempted to reproduce the function
of YouTube, some part of it imposed difficulty. For
example, the list of soaring videos on the exploration
tab and query search could be implemented with the
current YouTube Data API. However, the list of
recommended videos for a user displayed on the
home tab could not be implemented because it was
excluded from the current API. Also, even if the list
of subscribed channels is obtained, the list of videos
in order of posting date and time cannot be obtained.
Therefore, we conducted a pre-questionnaire to
simulate YouTube without using these unavailable
functions.
8 CONCLUSIONS AND FUTURE
WORK
We proposed a classification of video viewing task
types and a method for recommending videos