Increasingly, users connect to the Internet by mobile devices and they are generating massive content through them. The lead-off projects in Mobile Web 2.0 offer the opportunity to add semantics in order to obtain structured knowledge. In this paper, we present specific challenges for tagging reasoning, into the SinNet project. SinNet is based on user generated content (UGC) by mobile devices, as well as how to solve them by means of combining multi-agent systems and formal concepts analysis.