Xoops is a Content Managment System that uses a database to store data and create webpages on the fly when browsers send a request. This means most pages on your Xoops site will be created using a datbase query in order to render the pages. CMS websites using databases create query strings in urls like this http://docs.xoops.org/modules/xdocman/index.php?doc=xu-002&lang=en see the question mark here. There are others also.

It has been said that this kind of system is not 100% search engine friendly, because not all search engines will follow urls with query strings.

The good news is that Google will happily crawl and index Xoops sites and not only this, but Google serves its data to many other search engines. Many Xoops websites are very highly ranked and run successful commercial ventures.

There's more good news ... Xoops users have also developed some small modifications (hacks) to rewrite urls with query strings into search engine friendly addresses. This is an automated process that happens in the background.

With these hacks installed all xoops pages with access can be crawled and indexed.

There are many other issues regarding search engine indexing and ranking and these need more in depth treatment beyond this FAQ