This post will show you precisely how BM25 builds upon TF-IDF, what its parameters do, and why it is so effective.
Relevancy
KMW hosted the Boston Elasticsearch meetup group, and our own Rudi Seitz gave an in-depth talk about how relevancy works in a search engine. In this post learn about when he covered, including: how scoring is computed, query structure and analysis chains, and approaches to tuning relevancy.