Funding for this research was provided by:
National Research Foundation of Korea (NRF-2016S1A3A2925033, NRF-2016S1A2A2911945)
BK21 Plus Postgraduate Organization for Content Science
Text and Data Mining valid from 2020-01-30
Received: 9 June 2019
Accepted: 29 November 2019
First Online: 30 January 2020
: The authors declare that they have no competing interests.