7. The method of claim 1 , wherein: the assigned value represents a relevance probability of the first token; and the computing of the relevance value of the group of tokens is based on the relevance probability of the first token and further based on an irrelevance probability of the first token.
7. The method of claim 1 , wherein: the assigned value represents a relevance probability of the first token; and the computing of the relevance value of the group of tokens is based on the relevance probability of the first token and further based on an irrelevance probability of the first token. 8. The method of claim 7 further comprising: determining the irrelevance probability based on a proportion of descriptions that contain the first token within a set of descriptions.