The first aspect is the difference between topical and user relevance, which was
mentioned in section 1.1. A document is topically relevant to a query if it is judged
to be on the same topic. In other words, the query and the document are about
the same thing. A web page containing a biography of Abraham Lincoln would
certainly be topically relevant to the query “Abraham Lincoln”, and would also be
topically relevant to the queries “U.S. presidents” and “Civil War”. User relevance
takes into account all the other factors that go into a user’s judgment of relevance.
This may include the age of the document, the language of the document, the
intended target audience, the novelty of the document, and so on. A document
containing just a list of all the U.S. presidents, for example, would be topically
relevant to the query “Abraham Lincoln” but may not be considered relevant to
the person who submitted the query because they were looking for more detail
on Lincoln’s life. Retrieval models cannot incorporate all the additional factors
involved in user relevance, but some do take these factors into consideration.