Hi
Could you send me a link/article that explains this?
I am not aware of any. Aside from SEF extensions, specifically sh404SEF, nobody likes to talk about that ;)
This is a typical page of the site. If I remember well, the url comes from the menu item alias:
xxxx.com/children-greek.html
I thought this is the proper way to do it.
There's no "proper" way. If you use JOomla SEF URLs, then the links come from the menu items. If you use sh404SEF, the link comes from the category (optional)/article title.
As Joomla uses constantly an "Itemid" in its internal URls, and base the URls on it, the link to an article may depends on which page you linked
from. For instance, linking an article from the home page may create a link such as /children-greek.html, but linking the article from a module on another page might take another menu item and get you another link.
It does not happen usually for simpler sites, but it starts happening for more complex site, with modules linking to recent or latest or most sold items or similar.
With sh404SEF, the link will always be the same: /category/article-title (in addition, the links are highly conifgurable).
Let me rephrase that then: what do you mean by "All I want is to control the canonical tag of they duplicate pages."? Which "duplicates pages" are you talking about?
Rgds