Probabilistic Information Retrieval Why probabilities in IR? User Understanding Query Information Need Representation of user need is un certain How to match? Uncertain guess of Document Documents whether docum ent Representation has relevant content In traditional IR systems, matching between each document and query is attempted in a semantically imprecise space of index terms Probabilities provide a princi pled foundation for un certain reasoning Can we use probabilities to guantify our uncertainties?Probabilistic Information Retrieval 4 Why probabilities in IR? User Information Need Documents Document Representation Query Representation How to match? In traditional IR systems, matching between each document and query is attempted in a semantically imprecise space of index terms. Probabilities provide a principled foundation for uncertain reasoning. Can we use probabilities to quantify our uncertainties? Uncertain guess of whether document has relevant content Understanding of user need is uncertain