What is the difference between a REST web service and a SOAP web service?

Ref:-

http://javahungry.blogspot.com/2015/07/web-services-interview-questions-and-answers.html

Below are the main differences between REST and SOAP web service

• REST supports different formats like text, JSON and XML; SOAP only supports XML;

• REST works only over HTTP(S) on a transport layer; SOAP can be used different protocols on a transport layer;

• REST works with resources, each unique URL is some representation of a resource; SOAP works with operations, which implement some business logic through different interfaces;

• SOAP based reads can’t be cached, for SOAP need to provide caching; REST based reads can be cached;

• SOAP supports SSL security and WS-security(Web Service-security); REST onlysupports SSL security;

• SOAP supports ACID (Atomicity, Consistency, Isolation, Durability); REST supports transactions, but it is neither ACID compliant nor can provide two phase commit. 

Ref:-http://www.javaface.com/19-restful-web-service-interview-questions/

1) REST is more simple and easy to use than SOAP. REST language is based on use of nouns and verbs (better readability)
2) REST uses HTTP protocol for producing or consuming web services while SOAP uses XML.

• The SOAP WS is transport protocol neutral. Supports multiple protocols like HTTP(S),  Messaging, TCP, UDP SMTP, etc.
• The REST is transport protocol specific. Supports only HTTP or HTTPS protocols.

3) REST is lightweight as compared to SOAP and preferred choice in mobile devices and PDA’s. REST does not need XML parsing, no message header (to and from), hence less bandwidth
4) REST supports different format like text, JSON and XML while SOAP only support XML.

• The SOAP WS permits only XML data format.You define operations, which tunnels through the POST. The focus is on accessing the named operations and exposing the application logic as a service.
• The REST permits multiple data formats like XML, JSON data, text, HTML, etc. Any browser can be used because the REST approach uses the standard GET, PUT, POST, and DELETE Web operations. The focus is on accessing the named resources and exposing the data as a service. REST has AJAX support. It can use the XMLHttpRequest object. Good for stateless CRUD (Create, Read, Update, and Delete) operations.

GET – represent()
POST – acceptRepresention()
PUT – storeRepresention()
DELETE – removeRepresention()
5) SOAP based reads cannot be cached. REST based reads can be cached. Performs and scales better.

6) Different error handling:
REST: requires HTTP error handling
SOAP: can have user defined error

7) REST only supports synchronous  message because of its reliance of HTTP and HTTPS

8) SOAP WS supports both SSL security and WS-security, which adds some enterprise security features like maintaining security right up to the point where it is needed, maintaining identities through intermediaries and not just point to point SSL only, securing different parts of the message with different security algorithms, etc.
The REST supports only point-to-point SSL security. The SSL encrypts the whole message, whether all of it is sensitive or not.

9) The SOAP has comprehensive support for both ACID based  transaction management  for short-lived transactions and compensation based transaction management for long-running transactions. It also supports two-phase commit across distributed resources.
The REST supports transactions, but it  is neither ACID compliant nor can provide two phase commit across distributed transactional resources as it is limited by its HTTP protocol.

10) The SOAP has success or retry logic built in and provides end-to-end reliability even through SOAP intermediaries. REST does not have a standard messaging system, and expects clients invoking the service to deal with communication failures by retrying.