I have a problem: I created a website with joomla and I have a problem with the url ( example: www.mysite .com/index.php?option=com_content&view=article&id=51&Itemid=57 ). This url is indexed by google, but I can not create a Sitemap. you have solutions?
you can try to add a rewrite rule in you .htaccess file, so that urls like www.mysite .com/index.php?option=com_content&view=article&id=51&Itemid=57 can be transformed into www.mysite .com/index.php/com_content/article/51/57. Anyway there are no reasons why querystring url can not be inside an xml sitemap, I have plenty of them.
This is a common problem with Content Management Systems such as Joomla and Drupal - the CMS generates a link internally, and if you rewrite this link search engines may index both. The solution is to install a SEF (Search Engine Friendly) links module (Drupal has "clean URL's" you can turn on in core, while Joomla I believe has a SEF module), and then block the internal path using robots.txt. In Drupal, for example, the internal paths all begin with /node - so you would block these. With Joomla you would probably block /index.php? This will prevent duplicate pages from being indexed.