Slides presented at the Web & AI Seminar, National Institute of Informatics. Parts of the slides are taken from my dissertation defense (March 2010). We investigated the root of so-called "semantic drift" in Espresso-style bootstrapping algorithms using graph-theoretic approaches. It turned out that semantic drift is a parallel to the topic drift in the well-known link analysis algorithm, HITS (Kleinberg, 1999). We also showed that the regularized Laplacian reduces the effect of semantic drift, and is easy to use compared to the state of the art bootstrapping algorithm, Espresso.