1. A computer implemented method for retrieving documents from a collection of documents, the method comprising: identifying each document of the collection of documents; generating a word index for each document of the collection of documents, wherein each entry of the word index is an enriched-term string comprising a stemmed form of a word, an original form of the word, a separator character separating the stemmed form of the word from the original form of the word, a second separator character after the original form of the word followed by a lower-case version of the original form of the word and, before the stemmed form of the word, a first conceptual version of the word followed by a third separator character; generating a cross-documents list for the enriched-term strings wherein each enriched-term string is identified by an enriched-term identifier; and generating a cross-documents enriched-term occurrence table for matching each enriched-term identifier to the identified documents.