1. ["A Digital System Design Language (DDL)", J.R. Duley, IEEE Trans on Computers c-17(9), pp. 850-861, Sep 1968].
2. An adventure language developed by M. Urban, C. Kostanick et al of the UCLA Computer Club. DDL was the forerunner of ADL.
3. Data Definition Language.
4. Document Description Language.
5. Dynamic Data Exchange. (Originally "Linking").