Newbie Q: About namespaces in instance documents

I don't know whether this is on-topic; if not, perhaps someone would 
point me right.

All the examples I see of instance documents contain about a half-dozen 
namespace invocations on the header,
popularly two or three w3c xml citations, dublin core (one or two), 
maybe a few others. 

This seems to throw a lot of responsibility on the recipient. 
Is it valid if MySchema imports the various names and the instance 
document simply cites only MySchema?

Or is there more going on here than meets the eye?

-- 
David A. Cobb, Software Engineer, Public Access Advocate
"By God's Grace, I am a Christian man; by my actions a great sinner." -- The Way of a Pilgrim: R.French, Tr.
Life is too short to tolerate crappy software!