How to distinguish an architecture where data is transmitted only in one direction from an architecture where the information flow is bidirectional?

A unidirectional data flow architecture is characterized by a flow of information in one direction — from the source to the receiver. In such architectures, data flows down the chain, for example, from the model to the view.

In a bidirectional architecture, data can be transmitted in both directions — from the model to the view and back, allowing synchronization of state and response to changes from both sides.

Example:

• Unidirectional data flow: Flux, Redux — state changes through actions, data flows only downward.
• Bidirectional data flow: MVC with two-way binding (for example, in older versions of AngularJS) — changes in the UI are immediately reflected in the model and vice versa.

You can distinguish by whether there is a feedback mechanism that automatically updates the data source when the view changes. If yes — the flow is bidirectional, if not — unidirectional.