REST vs. SOAP: How to choose the best Web service?

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 not 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.madhukaranand.com/index.php?page=foo

becomes

http://www.madhukaranand.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.

Summary

SOAP

– A service architecture
– XML based
– Runs on HTTP but envelopes the message
– Slower than REST
– Very mature, a lot of functionality
– Not suitable for browser-based clients

REST

– A service architecture (resource-oriented)
– Uses the HTTP headers to hold meta information (although it is protocol-agnostic)
– Can be used with XML, JSON or whatever necessary
– Usually used with JSON due to the easily parsable content
– Faster than SOAP
– It uses semantic media types

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