Software or its components do not require a graphical user interface to communicate with each other. Softwares exchange data flow and functionalities through machine-readable interfaces also known as APIs (application programming interfaces).
API is a collection of programming codes that facilitates data transmission between products. It also contains the terms of this information exchange.
The objective of API specifications is to standardize information exchange between web services. Standardization represents the ability of different systems, written in diverse programming languages and/or operating on different OS s, or using different technologies, to seamlessly establish a communication link between one another.
1. Remote Procedure Call (RPC)
Web APIs comply with resource exchange principles based on Remote Procedure Calls. This protocol determines the exchange between client-server-based applications. One program (client) requests data/functionality from another program (server), located on a different computer on a network, and the server transmits the required response.
2. Service Object Access Protocol (SOAP)
A lightweight protocol, SOAP is employed for exchanging structured data in a distributed and decentralized environment. This specification includes the syntax rules for request & response messages transmitted by web applications. APIs complying with the regulations of SOAP allow XML messaging between systems through HTTP or Simple Mail Transfer Protocol ( SMTP) for transmitting mail.
3. Representational State Transfer (REST)
REST is a simpler alternative to SOAP, which many developers find challenging to use as it requires writing excess code to finish every task and heeding the XML structure for every message sent. REST follows another logic to make data available as resources. Each resource is characterized by a unique URL, and the user can request this resource by providing the URL.
Web APIs that comply with REST architectural constraints are identified as RESTful APIs. The APIs utilize HTTP requests (methods or verbs) to function with resources which include: PUT, GET, HEAD, CONNECT, POST, TRAC111111E, PATCH, OPTIONS, and DELETE.
RESTful API support messaging in different formats including plain text, HTML, XML, YAML, and JSON, while SOAP simply supports XML. The capability to support numerous formats for storing and exchanging information is one of the grounds REST is a dominant choice for building public APIs.