We have common definitions for process, business rules, operational decisions, business events and other things that are important to process modeling. And, I have mentioned my favorite ones (here). But we frequently ignore one of the very important aspects of process modeling: interactions. Fingar and Smith mentions in ‘Business Process Management, the Third Wave' that an interaction is the use of process desktops that allows people or participants to interact with the process. This includes workflow emphasizing assignment, task management and form-based data entry. So, interactions gave rise to the idea of task oriented process instances that are started by a form. We see this in today’s process monitor and task list in most BPM suites. A form is a completed interaction that spawns an instance. This was, arguably, a new concept in 2002.
The BPMN 2.0 specification (here) also delves into the concept of interactions. Section 10.1 says that a public process represents the interaction between a private business processes and another processes or participants. The interaction is the glue. In the specification, human interactions are a type of task with human involvement. Manual and human tasks have particular icons in BPMN that indicate that human involvement is required to complete the task. See the two figures below.
The Human Task & Manual Task
Remember: a manual task is a task that is expected to be performed without the aid of any digitized business process. An example might be the nurse delivering medication to a patient. This is contrasted with a user task which is performed with the assistance of a software application or is scheduled through a task list manager. An example would be the approval of a request or deciding a proposition.
Interactions are critical to the concept of choreography. A key characteristic of choreography is that it is an activity representing an interaction between two parties rather than a unit of work. According to Dumas, "The Fundamentals of Business Process Management”, the interaction can be one-way, where a message is exchanged or two-way, where messages exchanged bring a return message. Each message has an initiator and a recipient. Indeed, the BPMN spec states that "choreographies formalize way business participants coordinate interactions. This gives rise to the 'conversation' shape center defined in the spec.
In Wikipedia the interaction is defined as ‘a kind of action that occurs as two or more objects have effects upon one another’. This is fundamental in the concept of the business process.