The URL here is wrong: It will always take you to the live site.  We want each copy of BetyDB to link to its own copy of the schema documentation.  And there should be an "s" at the end of schema.

So if you had &lt;a href="https://betydb.org/schemas" target="_blank">Schema&lt;/a>, the link would show you the schema on the live site (once we put it up there), but then it would get confusing, because if you were on a test site instead of the live site, you would suddenly be switched to being on the live site.

For internal links (that is, for links from one part of BETYdb to another part of BETYdb), you should always use the Rails "link_to" function.  Look at the two links you are removing for an example of how this is used:

    <li><%= link_to "User Guide (PDF)", user_guide_path %></li>
    <li><%= link_to "Data Entry Guide (PDF)", data_entry_guide_path %></li>

"link_to" takes two arguments: First the text you want to appear for the link.  Second, the place to link to.  This could be a quoted full URL like "https://www.betydb.org/schemas", or a quoted relative URL like "/schemas".  But for internal links, it is best to use a named route.  Since Yilin added

    resources :schemas

to the routes.rb file, this automatically creates a named route to the schema documentation called `schemas_path`.  (See the pp 343-344 or the Rails Tutorial for more information about named routes, especially Table 7.1.  Also, some examples of using `link_to` appear on pages 254 and 255.)

So the full line in your case should be:

    <li><%= link_to "Schema", schemas_path %></li>