A1: User has sufficient knowledge for initial query.
A2: Relevance prototypes are “well-behaved”.
Term distribution in relevant documents will be similar
Term distribution in non-relevant documents will be different from those in relevant documents
Either: All relevant documents are tightly clustered around a single prototype.
Or: There are different prototypes, but they have significant vocabulary overlap.
Similarities between relevant and irrelevant documents are small
User does not have sufficient initial knowledge.
Misspellings (Brittany Speers).
Cross-language information retrieval (hígado).
Mismatch of searcher’s vocabulary vs. collection vocabulary
There are several relevance prototypes.
Contradictory government policies
Pop stars that worked at Burger King
Often: instances of a general concept
Good editorial content can address problem
Report on contradictory government policies