8. The one or more computer storage media of claim 7 , wherein determining whether to perform analysis of additional levels of tiers comprises evaluating whether one or more posting lists are long, wherein if one or more long posting lists are identified then at least one lower level tier from the one or more long posting lists is ignored and matching between posting lists is performed by consideration of combinations of other posting lists such that the at least one lower level tier from the one or more long posting lists is assumed present and resulting matches are deemed usefully close to an intent of the search query.
9. The one or more computer storage media of claim 8 , wherein the method further includes determining overall ranking values for documents by assuming presence of one or more atoms corresponding with the one or more long posting lists in documents from the other posting lists and assigning a nominal value to compute the overall ranking values for the documents.