Choosing the right API for your project first means understanding the different types of APIs out there. The most popular type is known as a Web Service, or Web API. A Web API provides an interface for web applications, or applications that need to connect to each other online to communicate. Web APIs exploded exponentially in 2017, and are predicted to only keep growing in 2018. In this blog, we'll explore the most popular sub-types of Web APIs: REST, JSON-RPC, XML-RPC, and SOAP.
REST (or RESTful) APIs are one of the most popular choices for API development. They are designed to use existing protocols, and typically are used with HTTP. REST can be used over most existing protocols, however. This means developers don't have to install libraries or additional software to take advantage of a REST API.
Since data isn't tied to methods and resources, REST can handle multiple types of calls, change structurally with the correct implementation of hypermedia, and return different data formats. One downside to REST, however, is the loss of ability to maintain state, which can make it difficult for newer developers to use. It's important to understand what makes a REST API RESTful, and why these constraints exist before building your API. If you don't, then you're more likely to have issues when developing.
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SOAP was designed back in 1988 by Bob Atkinson, Mohsen Al-Ghosein, Don Box, and Dave Winer for Microsoft. They designed it to offer a new protocol and messaging framework for the communication between applications over the web. While SOAP can be used across different protocols, it requires a SOAP client to build and receive different requests, and replies on Web Service Definition Language and XML.
SOAP wasn't immediately supported in all languages, and could often be a tedious task for developers to integrate with WSDL in its early years. However, SOAP calls can retain state, something that other APIs cannot do, and that may be attractive to developers.
XML-RPC and JSON-RPC
Remote Procedure Calls, or RPC APIs have the benefit of being easier - and faster - to implement than SOAP. It was the basis for SOAP, though many developers continue to use it generically, using it to make simple calls over HTTP with the data formatted as XML.
Similar to SOAP, RPC calls are tightly coupled and require the user to know the procedure name, as well as sometimes the order of parameters. This means developers have to spend a lot of time going through documentation to utilize an XML-RPC API. It's also vital to keep documentation in sync with the API, because otherwise the developer's integration attempts will fail.
While JSON was marketed as an improved XML, the downsides of an RPC API still exist, mostly in prominently coupled URIs.