Modelling and Predicting the Data Availability in Decentralized Online Social Networks

Maintaining data availability is one of the biggest challenges in Decentralized Online Social Networks (DOSN). In the existing work of improving data availability in DOSN, it is often assumed that the friends of a user are always capable of contributing sufficient storage capacity to store all the data published by the user. However, this assumption is not always true for today's Online Social Networks (OSNs) for the following reasons. On one hand, the increasingly more data are being generated on the OSNs nowadays. On the other hand, current users often use the smart mobile devices to access the OSNs. These two factors cause the shortage of the storage capacity in DOSN, where the published data are supposed to be stored within a friend circle. The limitation of the storage capacity may jeopardize the data availability. Therefore, it is desired to know the relation between the storage capacity contributed by the OSN users and the level of data availability that the OSN can achieve. This paper addresses this issue. In this paper, the data availability model over storage capacity is established. Further, a novel method is proposed to predict the data availability on the fly. Extensive simulation experiments have been conducted to evaluate the effectiveness of the data availability model and the on-the-fly prediction. The data availability model can be used by the OSN designers to determine the storage capacity for the published data in order to achieve the desired data availability. The on-the-fly prediction method can help the data replication and storage policies make judicious decisions at runtime.