Add the domain entity declaration (.ent) file to concept.dtd. In your copy of
concept.dtd, find the comment that says "DOMAIN ENTITY DECLARATIONS" and following this comment
add the following parameter entity declaration and reference:
<!ENTITY % xml-d-dec
The system identifier needs to reflect the actual location of the xmlDomain.ent file. The
example assumes that concept.dtd and xmlDomain.ent are in the same directory.