DDMSence (pronounced "dee-dee-em-Essence") is the only open-source Java library that fully supports the DoD Discovery Metadata Specification (DDMS). It converts DDMS Resources (also called assertions or metacards) into a Java object model, allowing them to be manipulated or traversed within the context of a Java environment.
The DDMSence source code is published under the GNU Lesser General Public License (LGPL). The complete text of this license can be found on the DDMSence website.
DDMSence is no longer under active development (as the DDMS specification has not been funded in years), although I continue to maintain the library for any legacy users.