The understanding of the user temporal behavior is a crucial aspect for all those systems that rely on user resources for daily operations, such as decentralized online social networks (DOSNs).Indeed, DOSNs exploit the devices of their users to take on and share the tasks needed to provide services such as storing the published data. In the last years, the increasing popularity of DOSN services has changed the way of how people interact with each other by enabling users to connect to these services at any time by using their personal devices (such as notebooks or smartphones).As a result, the availability of data in these systems is strongly affected (or reflected) by the temporal behavior of their users in terms of connections to DOSNs. In this paper, we propose the use of linear predictors to address the problem of the availability of user devices and, hence, data in DOSNs. To validate the proposed approaches, we evaluated their performance conducting a set of simulations exploiting a dataset of temporal information concerning the connections to Facebook collected from a set of users.
KEYWORDSavailability prediction, decentralized online social networks, user behavior
INTRODUCTIONIn the last years, online social networks (OSNs) have proliferated by attracting millions of users that share a large number of contents with each other. According to the International Telecommunication Union (ITU)*, OSNs have reached a global penetration rate of 31%. The evolution of mobile technology (such as smartphones and tablets) is the major driver that makes social networking the most popular online activity, which captures 30% of the time spent by users each day on the Internet † , i.e., about 1 hour and 50 minutes. The most popular OSNs are based on a centralized architecture where the service provider takes control over users' information. However, the centralized structure has several relevant drawbacks. For instance, during the last years, users' privacy in OSNs becomes an ever-increasing concern because private information of the users is exploited by the centralized OSN providers for several purposes. 1,2 Privacy and system scalability are two of the main issues that have led to the decentralization of the social networks.A decentralized online social network (DOSN) 3 is an OSN implemented in a decentralized way (such as peer-to-peer architecture). For instance, Diaspora ‡ and Friendica § are two of the currently available DOSNs that attract more than 669 000 users, and they are based on a network of independent, federated servers that are managed by the users. RetroShare ¶ is another available DOSN that allows users to create friend-to-friend connection for sharing data. In DOSNs, there is no centralized authority since users' devices are exploited to store and manage users' data. For this reason, the decentralization of OSNs requires efficient solutions for dealing with data availability arising when users' devices disconnect from the system. Indeed, the problem of data availability occurs because data of a user should...