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API ​

Application Programming Interface (API) is a way for two or more applications/programs to communicate with each other.

With APIs, an application can easily be accessed via multiple canals: web interface, CLI, scripts, etc. For example, in a service-oriented architecture, web services are a type of API which use the internet as network.

The term API often refer to Web API, but it can be used for programming languages, operating systems, hardware, etc.

Types ​

  • Open APIs: publicly available, anyone can access it
  • Partner APIs: used to collaborate between business entities
  • Internal APIs: private APIs, not exposed on a public network (or, at all)
  • Composite APIs: combination of different data and services APIs

Protocols and architectures ​

REST ​

Representational State Transfer (REST) define constraints and standards to assure data consistency in web applications, especially APIs.

Constraints ​

  1. Client Server: enforces the separation of concerns between the UI and the data.
  2. Stateless: no session is stored by the server, the client's request contains all information necessary to fulfill it.
  3. Cache: response is labeled has cacheable (or not), so the client can reuse it.
  4. Layered: client doesn't know if it's connected to the end-server or middlewares.
  5. Code on demand (optional): extend or customize functionality of client by transferring code
  6. Uniformity: 4 constraints ensure a uniform interface
    1. Identification of resources, in a clear and unique fashion
    2. Manipulation of resources, by the use of representations
    3. Self-descriptive messages, by providing exhaustive information
    4. HATEOAS, to dynamically serve and discover related resources

Resources ​

  • Usually in JSON or XML format
  • Can be…
    • Static (post, article, …)
    • Dynamic (weather data, satellites, …)
    • Intangible (stock prices, …)
    • Material (vending machine, dispenser, …)
  • URL access
    • Nested: GET Nested: GET /api/posts/10/comments
    • Flat: `GET /api/comments?postID=10``

Resources ​