1. A method of implementing protocol agnostic messaging between a workflow host and an executing workflow instance, said method comprising: receiving, from a user, a selection of a predefined workflow data activity for modeling a messaging operation between a workflow and a workflow host; specifying a data source definition, said specified data source definition defining a data object for storing message data to be communicated between an executing instance of the workflow and the workflow host, said workflow host instantiating the workflow instance; binding the selected data activity to the specified data source definition; and referencing the bound data activity as one of a plurality of activities in the workflow to implement messaging between the workflow and the workflow host.