2.Online video sharing applications become more and more popular. An online video sharing application allows users to record videos, and share with friends. Users need to register in the system by creating an account in the system with a unique username and password. Users are able to add or delete other users into or from their friend lists. The system has three Video Lists for each user. The first Video List contains the videos submitted by the current user. The second Video List contains the videos of friends. The third Video List is composed of recommended public videos from friends or non-friends. Users can write comments for videos of all the three lists. Users can only delete videos of the first list. A rubbish bin is used to contain deleted videos. (2) Build a state diagram for the status of video in the system. Tips: Before a video is submitted, it is just a draft. During the draft status, it can be set to be viewed by the user only (private) or viewed publicly. After the video is submitted, it changes into a waiting-for-check status. Only after the video is checked by Administrators of the platform, it can be viewed by others. The user can change the video between public and private statuses. The user can also delete the video. After deleted, the video is put into rubbish bin. Videos in the rubbish bin will be remove finally after 30 days, users can recover them before that time. (13')