File descriptions
=================
auth_users.csv - contains information about the registrants.
course.csv - contains information about the courses
course_enrollment.csv - contains courses enrolled by users
forum.dat - contains information about the post on forum’s

** note: 
- *.csv is separated by comma, and can be viewed by MS Excel (recommended) and plaintext viewer (i.e. notepad).
- *.dat is separated by '\t' (tab key) since the body of the forum posts may contain comma.


Data Fields
===========
auth_users.csv
- userid
- username
- date_joined
- name
- gender
- year_of_birth
- level_of_education
- mailing_address
- goals
- country
- city

courses.csv
- courseid
- course_name
- create_time
- enrollment_start
- enrollment_end
- start
- end
- effort: expected working hour/week
- length
- categroy: the categories of the course, separated by ' ' (space)


course_enrollment.csv
- userid
- courseid
- created: date a user enrolled the course

forum.dat
- id: the post id
- userid
- courseid
- type: two types in all, "CommentThread(主题帖)" is the post which has a title(topic), while "Comment(评论)" post is the comment to CommentThread
- comment_thread_id: only for Comment type, contains the comment_thread_id to which the comment reply
- created
- updated
- last_activity: only for CommentThread type, the last 
- title: only for CommentThread
- body: the body of the post
- comment_count: only for CommentThread, the number of comments under this post
- vote_up: the number of vote-up (点赞数)
- vote_down: the number of vote_down (opposite to vote_up)


