An agent (of a party) is an actor that is executing an action on behalf of that party. As, and in the context where the actor is doing this, we say that it fulfills the role of agent for that party. We also say that the party fulfills the role of principal (for that actor).
Being an agent (or principal for that matter) is a role (characteristic/property) that an actor (or a party, respectively) only has at a point in time where the actor is actually executing an action on behalf of that party.
During the time interval in which the action is executed, the actor may execute other actions in other execution-contexts, on behalf of the same or another party. However, for the execution of a single action, the actor is an agent for precisely one principal.
Agents are expected to access (and hence have access to) the policies that their respective principals provide in order for these agents to execute actions in compliance therewith. This, and relations with other concepts are described in the Parties, Actors and Actions pattern.
The purpose of the concept agent is that it is an enabler for the capability of determining its principal, because it is an actor with the property that it is executing some action on behalf of a party) - its principal. The relevance of this capability finds its origin in the fact that it is not the actor that is held accountable for the actions it executes, but the party on whose behalf they are are executed.
- When a person (as an actor) is doing something on its own behalf (as a party), it is both its own agent and its own principal.
- A person that does things for his employer acts as an agent for that employer.
- An ambassador, when (s)he is 'in function', acts as an agent for the country for which (s)he is ambassador.
- A person that fills in the tax return form for another person or organization acts as an agent for that person or organization.
- A company that makes cars may use robots that weld parts of a car together; whenever these robots are welding parts together, they acts as agents for that company.
- A (running) webserver that accepts product orders for a retailer acts as a (digital) agent for that retailer.
- A wallet app that runs on a phone and that is exclusively used by a single person acts as a (digital) agent for that person, and the latter is its principal.
- When an enterprise hires an accountancy-firm to produce an accountants-report, and the latter assigns an accountant the task to actually do this, and if the accountant does so as an employee that
works forthe accountancy-firm (see the parties, actors and actions model), then the accountant acts as an agent and the accountancy-firm would be the principal. However, the accountant could also be 'outsourced' to the enterprise (in which case the enterprise would have onboarded the accountant) specifically for producing the accountants-report, then the accountant would be an agent for the enterprise, and the latter would be its principal.