Validating a SKOS document

Hi,

I'm completely new to Web Semantic stuff... I've started learning RDF,
SKOS, etc. 3 days ago, so please don't shout at me :)

I'm trying to convert several thesauri into SKOS. Currently I'm trying
to create by hand a valid SKOS file describing on particular term
(Concept).

Enclosed, you will find a valid simple SKOS file and a non-valid file.
The second file is not valid because I don't understand how to extend
SKOS model. Right now, RDFS seems too complicated for me, and all
examples I found are in Turtle...

For instance, I have declared a "copy" of skos:related named "viewAlso" :
    <rdf:Property rdf:ID="viewAlso" rdfs:label="viewAlso">
        <rdfs:subPropertyOf
rdf:resource="http://www.w3.org/2004/02/skos/core#related"/>
    </rdf:Property>

How to use it now ? As you can see I have put some ???:viewAlso
because I don't know what to put instead of ???.

In fact I have another problem. In fact, the RDF validator does not
like http://example.com/thesaurus/cis#. If I understand well, this URI
should return a HTTP 200 code, isn't it ?

Thanks in advance.
Julien