When your application sends a ToolTalk request, it expects one tool to perform the indicated operation, or to answer the inquiry, and return a reply message. For example, if your tool sends the Desktop Services message Get_Modified, it should expect notification that the message was delivered and the action performed. The ToolTalk service guarantees that either a reply will be returned by the receiving process or the sender will be informed of the request's failure.
By identifying the operations requested by your tool that can fail
By identifying the operations your tool can perform for other tools
By identifying the operations your tool will want other tools to perform
A good method to use to identify these operations is to develop a scenario that outlines the order of events and operations that you expect your tool to perform and have performed.