I. Introduction
View to the vast amount of information exists on the internet and with the increasing of users demands for relevant information, the development of relevant information retrieval systems is necessary to meet these needs. The information retrieval varies from several parties mainly indexing process, the latter not consists only to classify documents but also indexing them. Human indexing is plenty expensive and request a lot of time, so researchers recourse to use automatic indexing system to solve a part of the problem.