Abstract
This paper surveys page ranking factors used in the current WWW search engines, such as (1) relevance to query keywords, (2) freshness, (3) popularity, (4) citation rank and (5) page types. The relevance to query keywords have been studied in the traditional information retrieval researches. However, other factors are introduced into the WWW search engines in order to improve their ranking performance, because WWW contents are heterogeneous and changeable large-scale hypermedia. The freshness, the popularity and the citation rank are the factors introduced from a viewpoint of contents reliability. On the other hand, the relevance to query keywords and the page types are the ones corresponding to user's domain and task in problem solving. Selection and combination of these factors must be refined for satisfying user's information needs.
