ESL provides support for DDE via an ESL stimulus library.  A stimulus library is a specially written Dynamic Link Library (DLL). DLLs and stimulus libraries are discussed in the Programming Guide.

The ESL DDE stimulus library:

•Contains functions and subroutines that an ESL program can call.  These allow an ESL program to post DDE messages and manage DDE conversations.

•Defines stimulus events that an ESL program can invoke. These allow an ESL program to be notified of receipt of DDE messages.

The ESL program can participate in one or more DDE conversations, either as a client, a server, or both.  In many cases, the library provides a default behavior for DDE messages that allows the ESL program to ignore many of the low-level details of the DDE protocol.  Many ESL programs can participate in a DDE conversation by calling only a few of the DDE functions, and by responding to only a few of the DDE events.  In any case, either one or both of the participating applications can be ESL programs.