Search engines use several techniques for sorting or sorting pages arising from a search. Among the known techniques for exploring a set of web pages, some rely on semantics, a page being ranked as being all the more relevant if it comprises a large number of occurrences of the word or words searched for. These techniques are sensitive to a practice, known as “spamming”, aimed at causing the words commonly used by surfers in their search query to appear a very large number of times in a given page, this having the effect of causing the page to appear frequently to be relevant.
Other techniques are based on the topological structure of the web. These techniques take account at one and the same time of the existing links between the pages considered and properties of the pages themselves, such as whether a page belongs to a domain or to a network subdomain of the web. These techniques are generally based on a graph representation of the pages to be processed. They are appropriate to the classification of pages complying with given topological properties in the graph. These techniques are sensitive to a variant of the practice of “spamming” aimed at referencing a given page a large number of times, this having the effect of locally falsifying the topological characteristics of the graph of the web.
Some of the techniques utilizing the topological structure of the web consist in effecting a classification of the web pages by allocating to the various pages a rank which is dependent on the relations of one page with the others.
An example of such a procedure, known by the term “PageRank”, is used in the implementation of the Google™ search engine and is described in the document: “The PageRank Citation Ranking: Bringing Order on the Web”, by L. Page, S. Brin, R. Motwani and T. Winograd; Technical Report, Computer Science Department, Stanford University, 1998.
The PageRank procedure orders the pages as a function of their visibility on the web. In this procedure, random navigation from page to page around the web following the hypertext links is simulated. This navigation corresponds to that operated by a user accessing the web when the latter randomly activates one of the hypertext links located in a displayed page, so as to access another page. This procedure carries out a probabilistic analysis of this simulated navigation so as to determine the probability of the user being located in a given page during random navigation from page to page such as this. The rank of a page is all the higher the higher the number of times this page is cited by other pages.
Such a procedure provides a ranking which is not necessarily relevant as regards the search performed by a user, the best ranked pages (of highest rank) not necessarily being the pages corresponding best to the user's expectation.
Furthermore, this procedure does not make it possible to identify in the set of documents thematic communities or communities of interest, apt to steer the user more rapidly to an interesting page, nor even to perform a classification of the documents found by thematic community.