performance changes of two popular search engines, yahoo! and google, in terms of indexing coverage and the effectiveness of metadata elements

purpose: this paper aims to evaluate the performance of two public search ensiges, including yahoo and google in terms of their indexing coverage and the effectiveness of metadata elements on web page ranking. method: the effectiveness of the five metadata elements including html title tag, html keywords and description meta-tags, title and subject metadata elements from dublin core, which focus on subject representation of the web pages, were examined using the experimental method. the 93 web pages were designed and submitted in two different time periods; first on http://metadata.irandoc.ac.ir and then on http://metadata.um.ac.ir. the process of indexing of both search engines was recorded. unique and repeated keywords embedded as metadata elements were searched, and the significant differences between rankings of the two groups were examined by non-parametric u mann-whitney test. the wilcoxon test was also applied to evaluate the performance stability. findings: findings reveal the significant role of html title tag and unique description meta tags in web page visibility in both periods. duplicate keywords actually harmed rankings in google public search engine and this was stable during the time.