Supervised methods recast keyphrase extraction as a binary classification task (Witten et al., 1999), whereas unsupervised methods apply different kinds of techniques such as language modeling (Tomokiyo and Hurst, 2003), clustering (Liu et al., 2009) or graph-based ranking (Mihalcea and Tarau, 2004).
the completeness of the graph has the benefit of providing a more exhaustive view of the relations between topics.