1. A computer-implemented method for creating an inverted index of a subset of data, comprising: executing in a computer system processor a software component of a computer program product, wherein said executing of the software component configures the computer system to perform: a first step of receiving from computer storage: a set of data; a first inverted index of said set of data; and identifiers of a subset of data of said set; and a second step of creating, without reprocessing the data identified by said identifiers, a second inverted index using only the first inverted index and said identifiers, said second inverted index being both an inverted index of said subset of data and a subset of said first inverted index, wherein said second step of creating comprises comparing the first inverted index with said identifiers, and wherein said second step does not make use of data of the set which are not in the subset or identifiers of data of the set which are not in the subset.