Integrating user interface agents with conventional applications

In most experiments with user interface agents to date, it has been necessary either to implement both the agent and the application from scratch, or to modify the code of an existing application to enable the necessary communication. Instead, we would like to be able to "attach" an agent to an existing application, while requiring only a minimum of advance planning on the part of the application developer. Commercial applications are increasingly supporting the use of "application programmers' interfaces" and scripting languages as mean of achieving external control of applications, Are these mechanisms sufficient for software agents to achieve communication with applications?