ABSTRACT
In addition, applying key-enforced access control to soware as a service remains a challenge. For example, the collaborative editing service (e.g., Google Docs, Oce Online, and Cloud9) has become a popular and convenient choice for online users. With such a service, a group of users can cooperatively edit documents through the Internet; in particular, they can concurrently modify the same document, even write on the same line. Meanwhile, the collaborative editing cloud service provides consistent views to all clients in a timely manner; for example, if each of two independent users concurrently inserts one character into the same line that is displayed identically on their own screens, all users will immediately see both of these characters appear in the expected positions.
