Drawbacks of the TF-IDF model

Suppose, on an e-commerce website, a customer is searching for a jacket and intends to purchase a jacket with a unique design. The keyword entered is unique jacket. What happens at the Solr end?

http://solr.server/solr/clothes/?q=unique+jacket

Now, unique is a comparatively rare keyword. There would be fewer items or documents that mention unique in their description. Let us see how this affects the ranking of our results via the TF-IDF scoring algorithm. A relook at the scoring algorithm with respect to this query is shown in the following diagram:

A relook at the TF-IDF scoring algorithm

The following parameters in the scoring formula do not affect the ranking of the documents in the query result:

• coord(q,d): This would be constant for a MUST query. Herein we are searching for both unique and jacket, so all documents will have both the keywords and the coord(q,d) value will be the same for all documents.
• queryNorm(q): This is used to make the scores from different...