XML Namespaces

[SwetaG@riskinc.com]

Hi,
Q-1 Suppose i have the follwoing XML with namespaces
<!ELEMENT foo:A (foo:B)>
   <!ATTLIST foo:A
             xmlns:foo CDATA #FIXED "http://www.foo.org/">
   <!ELEMENT foo:B (#PCDATA)>
]>
<foo:A xmlns:foo="http://www.foo.org/">
     <foo:B>abcd</foo:B>
  </foo:A>

should the URL http://www.foo.org/ used as XML Namespaces actually
physically exist or i am giving any assumed URL at my own??

If it phisically exist then from where do i get it?Do i have to pay and get
it..is there any service that provides it.

if once i got that URL and it is known to other person in the organization
and that person starts using it being in assumption that i am not using it
how do i control that...

and if URL is my assumed name how can i be assured that the URL i am using
is not used by any other person in the same organisation or outside the
organisation.

Supoose i have used http://www.foo.org/ in my xml document as the name
space and some other person in the organisation or out side the
organisation happens to use the same http://www.foo.org/.....(if its an
assumed name and it might happen that other person can assume the same name
as in case of the same element name in the XML document)...then how do i
control that??
Rgards,
Sweta