What is difference between blog id and site id?

Question

The going through the mu functions source I come across references to two different ids for sub-blogs - site id and blog ids. In what context is each used?

Answer 1

• site_id = the ID of the parent site (the domain, eg. wordpress.com)
• blog_id = the ID of the parent site's blog(s) (usually sub-domains, eg mary.wordress.com)

Answer 2

In a Multisite install (and also since WordPress 3), you can have a several blogs (identified in the database model by blog_id) within one site (identified in the database model by site_id).

The thing that I found confusing in this context, though, is that most of WordPress code and documentation will use a terminology that differs from the database model. They refer to a blog using the word site, and to a site using the word network.

For example, this section of the Codex refers to the Site URL (as defined in the WP_SITEURL constant), which really is the URL of the blog URL in multisite context.