Hi,

I am a newbie to programming using XML and I'm currently working on a
side-project which will house some database information in a XML-file.
I am writing a DTD to specify the XML-format, mostly for the purpose of
documenting the XML database.

My issue is that I have some fields, e.g.
<!ELEMENT Vehicle ( Car? )>
<!ELEMENT Car ( Gasoline | Diesel )>
<!ELEMENT Gasoline EMPTY>
<!ELEMENT Diesel EMPTY>

but I want to make sure that this database is extendable. I.e. after
using the database for a while in my application I want to be able to
add stuff that I come up with later on, e.g.
<!ELEMENT Motorcycle ( Sportbike | Harley )>
<!ELEMENT Sportbike EMPTY>
<!ELEMENT Harley EMPTY>

I'd rather not add a lot of "Reserved"-elements in the DTD, as this is
not a nice solution. My own little idea is that i'm anyway able to add
items to the DTD further on since I both have the DTD of the XML and
the source of the application using it. Is this correct?

I've looked around and found another way to do this and that is to
include the old DTD as an entity, is that the way to go?

Please excuse my newbie-question, I just want to know if my way of
thinking is correct.

Thanks a lot for reading!