Basic Namespace

Hi,

I am new to this forum. I have one very basic question about RDF, I hope you
all can help:

In defining the Namespace as follows:

rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'
vCard='http://www.w3.org/2001/vcard-rdf/3.0#'
dc= 'http://purl.org/dc/elements/1.1/'
edu='http://www.example.org/'


1.) Why some ended with '#' and some can be ended with '/'?
2.) Why have 2 different format?
3.) What is the '#' means?


Hope someone can help.

Thanks.

Cheers,
Nomad