1972
Karen Spärck Jones publishes IDF
Karen Spärck Jones introduced inverse document frequency (IDFInverse document frequency — a search ranking signal that weights rare terms more heavily.) in 1972 — a cornerstone of search ranking and information retrieval.
What it was for
IDFInverse document frequency — a search ranking signal that weights rare terms more heavily. weights rare terms higher in search — the 'idf' in tf-idf used by Elasticsearch, Lucene, and early Google. Her work predates the web but powers every search engine developers integrate with.
People
- Karen Spärck Jones — researcher
Why it's here
IDFInverse document frequency — a search ranking signal that weights rare terms more heavily. is foundational math behind modern search ranking.
Why it mattered
It quantified term importance across document collections.
What it solved
Keyword matching alone ranked common words as important as distinctive ones.
Media
ImageKaren Spärck Jonesen:user:Markus Kuhn, CC BY 2.5, via Wikimedia Commons