Differences between SOAP and REST API

The following are the differences between SOAP and REST API.

SOAP has been preferred for services within the enterprise and
REST has been preferred for services that are exposed as public APIs.

And also Compare to SOAP , the advantage of REST API lies with performance: with better cache support, lightweight requests and responses, and easier response parsing, REST allows for nimbler clients and servers, and reduces network traffic, too.

You access rest API in the form of URL's. Normal URL's which you type in your address bar. 

SOAP API on the other hand involves downloading a WSDL file, Converting the WSDL files to regular classes and then invoking methods on those objects.

SOAP API and REST API are two commonly used API's to expose your data from force.com platform to the other platforms(JAVA , .NET ,etc) or to allow external application to invoke Apex methods.

What is SOAP ?

The Simple Object Access Protocol (SOAP) is an attempt to define a standard for creating web service APIs. It is a pattern, a web service architecture, which specifies the basic rules to be considered while designing web service platforms. It typically uses HTTP as a layer 7 protocol, although this is not mandatory. The SOAP message itself consists of an envelope, inside of which are the SOAP headers and body, the actual information we want to send. It is based on the standard XML format, designed especially to transport and store structured data. SOAP may also refer to the format of the XML that the envelope uses.

SOAP is a mature standard and is heavily used in many systems, but it does not use many of the functionality build in HTTP. While some consider it slow, it provides a heavy set of functionality which is a necessity in many cases. It might now be the best solution for browser-based clients, due to its custom format.

What is REST ?

The Representational State Transfer (REST) is another architectural pattern (resource-oriented), an alternative to SOAP. Unlike SOAP, RESTful applications use the HTTP build-in headers (with a variety of media-types) to carry meta information and use the GET, POST, PUT and DELETE verbs to perform CRUD operations. REST is resource-oriented and uses clean URLs (or RESTful URLs).

For example :

http://www.developingthefuture.com/index.php?page=foo

becomes

http://www.developingthefuture.com/foo

This kind of URLs syntax greatly improves both visibility and usability. It doesn’t use any query strings, and it also provides certain SEO benefits (the crawlers just love plain text). The body of the REST message can be XML, JSON or any other format, although JSON is usually the preferred choice. On the other hand, you can’t use JSON with SOAP. Or at least not entirely, because SOAP uses XML by definition for it’s envelope. It should also mentioned that REST is, by design, protocol-agnostic, although it is usually used with HTTP. 

SOAP API

1)Supports data in the form of XML only 2)Requires WSDL for the integration 3)Use SOAP API in any language that supports Web services.

REST API

1)Supports both XML and JSON format 2)Preferred for mobile and web apps since JSON being Lighter the app runs smoother and faster