define-dde-client defines a mapping from the symbol name to the DDE service name with which to establish a conversation, and the conversation class to use for this conversation. The argument service is a string which names the DDE service. It defaults to the print-name of name. The argument class is a subclass of
dde-client-conversation which is used for all conversations with this service. It defaults to
dde-client-conversation. Specifying a subclass allows various aspects of the behavior of the conversation to be specialized.
Note that it is generally not necessary to register client services unless a specialized conversation type is required. However, it is sometimes convenient to register a client service in order to allow the service name to be changed in the future.
LispWorks User Guide and Reference Manual - 13 Feb 2015