OAPI is different compared to API. What is inside an OAPI?

In the context of OutSystems architecture, the term "OAPI" is likely used to refer to the internal Application Programming Interface of an OutSystems module, specifically a Service Module. The core component of this interface, used to expose reusable, non-breaking business logic and functionality to other modules within the same environment, is the Service Action. This provides a strongly-typed, compile-time-checked contract between modules. This is distinct from a REST API, which is a technology used to expose functionality over web standards (HTTP) primarily for external systems or decoupled front-ends.

B. REST API: A REST API is a specific type of web service interface for exposing functionality, not a component inside the fundamental, internal API of a Service Module. A REST API method typically calls a Server Action to execute its logic.

1. OutSystems Official Documentation

"Service Actions": "A Service Action is a public Server Action in a Service Module. It encapsulates a piece of business or integration logic and can be reused across different modules... Service Actions are the key element for building a service-oriented architecture." This source establishes the Service Action as the key element of a Service Module's reusable API.

2. OutSystems Official Documentation

"Designing the architecture of your applications"

The 4 Layer Canvas: In the section describing Core Services

it states: "They offer reusable business services... exposing a well-defined and non-breaking public API of Service Actions." This reinforces that the API of a Core Service module is composed of Service Actions.

3. OutSystems Official Documentation

"Expose REST APIs": "Expose REST APIs to make your application's data and functionality available to other systems." This document defines REST APIs as a mechanism for external exposure

distinguishing them from the internal

module-to-module communication facilitated by Service Actions.