It's the abstract sense that is important. Pagerank is a dimensionality reduction technique. It finds the first eigenvector of the transition matrix. Eigenvecto

It's the abstract sense that is important. Pagerank is a dimensionality reduction technique. It finds the first eigenvector of the transition matrix. Eigenvectors = PCA. LSI is basically PCA, but applied to the document-term matrix. LDA is a dimensionality reduction technique that makes use of more information.