For the second exercise of my Information Retrieval course at the university I had to do implement a relevance feedback system - so I thought: Why not build it upon drupal's search? So that's what I did. The result is a working proof of concept module, which you can find in my sandbox and test at the demo site. The system has two operation modes: One that uses "implicit feedback" and one that let's the user give "explicit feedback". The implicit feedback mode just tracks which search results the user has viewed, takes these results as relevant to generate an optimised search query and shows the improved results to the user. The explicit system works the same way, but provides some UI for users to mark results as relevant and non-relevant, as you can see on the screenshot: You can test the system at the demo site, which runs in explicit feedback mode. Once you have provided three positive results as feedback the system makes use of the Rocchio algorithm to generate an optimised search query and redirects you to the improved search results. As I've written this just for the university exercise I don't think I'll make a full ready module out of it. If you are interested in more details, check out the system documentation I've written or just contact me.