Make a local copy of the appropriate document type shell DTD. The DITA-defined declarations include both all the DITA-defined modules as well as base shells for all of the DITA-defined top-level topic and map types: map, topic, ditabase, bookmap, concept, reference, task, glossentry, and so on. These shells are intended to be used as the starting point for creating local customized shells that reflect your local topic and domain requirements.
Copy the concept.dtd file from the DITA distribution to some location outside the scope of the DITA Open Toolkit (e.g., c:\mystuff\dita\dtd\concept.dtd).