What are some theory problems in Information Retrieval and Search Engines which are not yet solved or can be bettered? I'm interested in IR and Search Engines and want to work on a theory problem in this space. Most thoughts that I get are focused towards implementation and would like to explore something not solved or can be bettered instead of implementing
Anaphor resolution:


  Since this type of understanding is still poorly implemented in software, automated anaphora resolution is currently an area of active research within the realm of natural language processing.