KinoSearch::Docs::IRTheory - Crash course in information retrieval.
Just enough Information Retrieval theory to find your way around KinoSearch.
KinoSearch uses some terminology from the field of information retrieval which may be unfamiliar to many users. "Document" and "term" mean pretty much what you'd expect them to, but others such as "posting" and "inverted index" need a formal introduction:
Since KinoSearch is a practical implementation of IR theory, it loads these abstract, distilled definitions down with useful traits. For instance, a "posting" in its most rarefied form is simply a term-document pairing; in KinoSearch, the class KinoSearch::Posting::MatchPosting fills this role. However, by associating additional information with a posting like the number of times the term occurs in the document, we can turn it into a ScorePosting, making it possible to rank documents by relevance rather than just list documents which happen to match in no particular order.
KinoSearch uses a variant of the well-established "Term Frequency / Inverse Document Frequency" weighting scheme. A thorough treatment of TF/IDF is too ambitious for our present purposes, but in a nutshell, it means that...
skate park,
documents which score well for the comparatively rare term skate will rank higher than documents which score well for the more common term park.skate and park will rank higher than a 1000-word text which also contains one occurrence of each.A web search for "tf idf" will turn up many excellent explanations of the algorithm.
Copyright 2007-2009 Marvin Humphrey
See KinoSearch version 0.30.
