metadata URL?

[John Dennis]

Most SP's and IdP's provide a URL endpoint which allows you to fetch 
their metadata. But how do you know what that URL is? It seems to me 
this is a slightly different than discovery (or is it?).

I have noticed what seems to be a convention with the limited number of 
SP's and IdP's I've dealt with, their entityID is their metadata URL. I 
don't think this is required by any specification. Is it a convention 
and if so does the convention exist to solve the problem of knowing 
where to fetch the metadata from and hence good practice?

Is there some other way in which the metadata URL is published?

-- 
John