In this paper, we address the problem of how toexploit folksonomy systems and social bookmarking tools toenrich DBpedia ontology while unifying the formal knowledge represented by DBpedia ontology with the informal knowledge emerging from tagging. Our approach taps into external tools such as the sense inventory WordNet to correct mistakes resulted from the free tagging and takes advantage from semantic relationships between tags to recognize resources' context. We performed evaluations with focus on the particularly challenging problem of resources' ambiguity to prove that not all resources shared in folksonomies are relevant resources for DBpedia ontology and to show that our pre-processing step increases precision values.