Does it have sense to include sitemap URL into sitemap?
It is pointing to itself and in SEO perspective it's no use because if crawler is on our sitemap he already knows it, no need to inform it, right?
<?xml version="1.0" encoding="UTF-8" ?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<url>
<loc>http://example.com/sitemap.xml</loc>
<lastmod>2014-03-22</lastmod>
</url>
</urlset>
Sitemaps are for telling search engines where to find your content, not your sitemaps. So you should not include your sitemap URL in your sitemap. (It would be redundant anyway).
Some of the sitemap generator or the deep link crawlers may cause a cyclic redundancy. However crawlers like Google bot, Bing bot are clever enough to understand this. Read the complete guidelines on https://support.google.com/webmasters/answer/183668?hl=en
This is described here.
If your site have large number of links, you can submit a single sitemap that will include all other sitemaps.
This is useful for Articles website/ Ecommerce etc
Actually you should include sitemap in sitemap if you have lots of URLs.
You can provide multiple Sitemap files, but each Sitemap file that you provide must have no more than 50,000 URLs and must be no larger than 10MB (10,485,760 bytes). If you would like, you may compress your Sitemap files using gzip to reduce your bandwidth requirement; however the sitemap file once uncompressed must be no larger than 10MB. If you want to list more than 50,000 URLs, you must create multiple Sitemap files.
<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<sitemap>
<loc>http://www.example.com/sitemap1.xml.gz</loc>
<lastmod>2004-10-01T18:23:17+00:00</lastmod>
</sitemap>
<sitemap>
<loc>http://www.example.com/sitemap2.xml.gz</loc>
<lastmod>2005-01-01</lastmod>
</sitemap>
</sitemapindex>
