Recent years have seen an increasing diffusion of online communities giving their members the ability of specifying and sharing metadata concerning online resources. Such practice, also known as social or collaborative tagging, has the purpose of collecting and sharing opinions about Web resources and simplifying their retrieval. In this paper, we go one step further and show how tags can have more enhanced applications to be exploited for customizing Web content fruition. More precisely, we propose a multi-layer framework where data collected by social tagging communities are complemented with additional services. Such services provide users the ability of expressing their dis/agreement with existing tags, denoting the members they trust based on their characteristics and relationships, or specifying policies on which "quality" assessment of resources should be returned. Besides providing the formal specification of the proposed framework, we illustrate two case studies we have implemented and the experiments we have carried out in order to verify the feasibility of our approach
