Rocchio algorithm

The Rocchio algorithm is based on a method of relevance feedback found in information retrieval systems which stemmed from the SMART Information Retrieval System which was developed 1960-1964. Like many other retrieval systems, the Rocchio feedback approach was developed using the Vector Space Model. The algorithm is based on the assumption that most users have a general conception of which documents should be denoted as relevant or non-relevant. Therefore, the user's search query is revised to include an arbitrary percentage of relevant and non-relevant documents as a means of increasing the search engine's recall, and possibly the precision as well. The number of relevant and non-relevant documents allowed to enter a query is dictated by the weights of the a, b, c variables listed below in the Algorithm section.

The formula and variable definitions for Rocchio relevance feedback is as follows:

${\displaystyle {\overrightarrow {Q_{m}}}={\bigl (}a\cdot {\overrightarrow {Q_{o}}}{\bigr )}+{\biggl (}b\cdot {\tfrac {1}{|D_{r}|}}\cdot \sum _{{\overrightarrow {D_{j}}}\in D_{r}}{\overrightarrow {D_{j}}}{\biggr )}-{\biggl (}c\cdot {\tfrac {1}{|D_{nr}|}}\cdot \sum _{{\overrightarrow {D_{k}}}\in D_{nr}}{\overrightarrow {D_{k}}}{\biggr )}}$

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