DITA Open Toolkit uses Apache XML Commons Resolver so that the references to DTD or XML Schema files in DITA files do not need to be updated each time when you change the file paths on your workstation or use another workstation.
With this feature, when a developer makes a new specialization, the developer only needs to
update the mapping between the new DTD file's system id (location relative to the catalog
file) and public id (the id assigned by the developer in the head of the DITA or xml file
which identifies the corresponding dtd file) in the catalog file
(