Explain the architecture of a typical RAP-based Fiori application?

A RAP-based Fiori app is built from several distinct, connected layers, each with a specific responsibility, working together to deliver data from the database to the user's screen.

flowchart TD
    A[SAPUI5/Fiori Elements frontend] --> B[OData Service - generated from Service Binding]
    B --> C[Service Definition - exposes selected CDS Views]
    C --> D[Behavior Definition - business logic, validations]
    D --> E[CDS View - data model]
    E --> F[Underlying database table]

Data and requests flow down through these layers (a save request from the UI eventually triggers behavior definition logic, which persists via the CDS View's underlying table), while query results flow back up. This layered structure is exactly what lets RAP separate concerns cleanly: UI logic in the frontend, business rules in the behavior implementation, and data structure in the CDS View, each independently maintainable without tightly coupling all the logic into one monolithic layer.