ROR sitemaps are completely useless. None of the search engines support them. But they all support the sitemaps.org format. Needless to say you want to use the on they support and ignore the one they don't.

Google sitemaps can be found by all engines by referring to them in the robots.txt file. For example, Sitemap: http://www.site.com/sitemap.xml

Thanks for your reply. Another question, Is a good idea have the the two sitemaps Google and Ror on a web?

There is absolutely no reason to have a Ror sitemap at all.

Ror sitemap promotes the concept of structural feeds or in XML format. While Google Sitemap creates a sitemap with HTML and images format

Actually a Google sitemap is in XML and is now the default format for all four major search engines. That's why Ror sitemaps are worthless. It's not only redundant but ignored by the search engines.

Thanks stymiee. Now I know that google sitemap is better that ROR sitemap.

on our site http://www.punjabcolleges.com, google sitemaps page was showing about 25000 pages to be in database, however it had indexed only 6-7000 pages. when we did checking, we noticed that our sitemap format was not exactly as per google specification. it was more of a rss sitemap. we think that xml sitemap is the best of all solution as far as sitemap for search engines is concerned. but there should not be harm in maintaining ror sitemap too, though may not be of much advantage either.

Google Sitemap is the best of all. You need to follow those standards for better results. If not things might get difficult for your website.