In order to decide which is best, we first have to briefly define what an API is in relation to web services. An API is a programmatic interface which uses a request / response system. This is usually transmitted as JSON data via a web server based on HTTP with varying levels of security and authentication. In order to determine which method is best you have to ask yourself some questions. What does your service get from the client? Does your service perform asynchronous processes often? And, how high is the security level that is required? Also, when all you have to do is query your service endpoints with a simple result being returned in the response, it may not make a difference which to use. But when you need to add HTTP headers and pass in parameters such as tokens and validation, run tests and debug, you can see that there are clear advantages and disadvantages of each approach.

A RESTful API (Representational State Transfer) in an architectural style mostly utilizing JSON, which is faster to parse than XML. JSON is very closely connected to object-oriented languages like JavaScript for web, JAVA, Kotlin, Objective-C, and Swift for mobile, etc. And can be parsed fast using the same object-based model as those languages. There is also the consideration of caching. REST sent over HTTP utilizes the caching and TLS security authentication features available in HTTP. However, we cannot always use the caching features implemented in the protocol for data that needs to be exchanged between the client and server fast such as trading stocks or currencies. Also, there is the concern about HTTP verb binding. Much of the RESTful APIs do not use all HTTP verbs in the way HTTP does. When creating new resources for example, most developers use POST instead of PUT, and POST instead of DELETE for deleting. This takes that additional functionality of HTTP out if not used.

SOAP (Simple Object Access Protocol) is a protocol to transmit logical operations and data in the form of XML. Each request we send to a SOAP service is an RPC "remote procedure call" representing an operation we want performed by the server, and it relies on confirming the state of the transaction which helps with accuracy. SOAP security is well standardized through WS-Security, whereas REST has to implement their own security. There can however, be a slow speed due to parsing XML and that higher security. It also relies on formal contracts where both sides (information provider and consumer of the data) have to agree on the rigid specifications that SOAP gives for the interactions.

In conclusion, if you need compatibility and speed, use REST. If you need to guarantee security and communication reliability, use SOAP.



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