Pre-indexing Pruning Strategies.

We explore different techniques for pruning an inverted index in advance, that is, without building the full index. These techniques provide interesting trade-offs between index size, answer quality and query coverage. We experimentally analyze them in a large public web collection with two different query logs. The trade-offs that we find range from an index of size 4% and 35% of precision@10 to an index of size 46% and 90% of precision@10, with respect to the full index case. In both cases we cover almost 97% of the query volume. We also do a relative relevance analysis with a smaller private web collection and query log, finding that some of our techniques allow a reduction of almost 40% the index size by losing less than 2% for NDCG@10.