Use of Schema.org

Dear all,

I'm new to RDF and is now lost in the world of schema, DBPedia, Schema.org
etc... so I'm seeking clarification on some of the queries I have on my
mind. Please feel free to comment!

So here goes for the queries:

1. My understanding is what Google/Yahoo/Microsoft proposed for Schema.org
is a schema that can be used for doing markup in HTML. It can also be the
"RDFS" for creating RDF.
So when I'm "creating an instance" for say a Place, I do the following (in
RDF/XML format):

<rdf:RDF xmlns:schema="http://schema.org/">

<rdf:Description rdf:about="Oslo">
<rdf:type rdf:resource="http://schema.org/place" />
<schema:name>Oslo</schema:name>
<schema:geo>
<schema:GeoCoordinates>
<schema:latitude>59.9149776°N</schema:latitude>
<schema:longitude>10.746544°E</schema:longitude>
</schema:GeoCoordinates>
</schema:geo>
</rdf:Description>

Is this understanding correct?



2. If the above is correct, what is the relationship between Schema.org,
DBpedia and Opencyc etc? Schema.org seems to be the same as Opencyc.
Schema.org is easier to read, while Opencyc is richer in schema content, am
I right?



3. If I choose to use Schema.org as my RDF schema, when I find something
that's not define in Schema.org, e.g. a "Farm", can I do the below
extension:


   <owl:Class rdf:about="AgriculturalOrganization">
        <rdfs:label xml:lang="en">AgriculturalOrganization</rdfs:label>
        <rdfs:subClassOf rdf:resource="http://schema.org/LocalBusiness"/>
        <rdfs:comment xml:lang="en">Food and agriculture
organization</rdfs:comment>
    </owl:Class>

    <owl:Class rdf:about="Farm">
        <rdfs:label xml:lang="en">Farm</rdfs:label>
        <rdfs:subClassOf rdf:resource="AgriculturalOrganization"/>
        <rdfs:comment xml:lang="en">A Farm.</rdfs:comment>
    </owl:Class>


and I used it like below:

xmlns:schext="http://example.com/SchemaExtension/"

<schext:Farm rdf:nodeID="My Farm">
<schema:name>My Farm</schema:name>
<schema:location rdf:resource="Oslo" />
</schext:Farm>


Is the above ok?


4. I noticed there is a mapping between vocabulary of DBpedia and
Schema.org. May I know is this mapping useful specifically for Search
Engines?

Thanks in advance for all helps!

Cheers,
Dorothy