SOAP – Protocol or Message Exchange Pattern

In a recent interview I have been asked What is SOAP? Is it a Protocol or Message Pattern. It’s stupid that i was confused by the question and simply said “Message Exchange Pattern”, to my knowledge As the name states it’s a Protocol. Message Exchange Pattern(MEP) is part of a SOAP, where the description of the pattern of message being  transferred are mentioned. Quite often mistakes happen,  but this will make me to learn from it and not to repeat the same again. Cool. Nice interview experience.

SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks. It relies on eXtensible Markup Language (XML) as its message format, and usually relies on other Application Layer protocols (most notably Remote Procedure Call (RPC) and HTTP) for message negotiation and transmission. SOAP can form the foundation layer of a web services protocol stack, providing a basic messaging framework upon which web services can be built. This XML based protocol consists of three parts: an envelope – which defines what is in the message and how to process it – a set of encoding rules for expressing instances of application-defined datatypes, and a convention for representing procedure calls and responses.

As a layman’s example of how SOAP procedures can be used, a SOAP message could be sent to a web-service-enabled web site (for example, a real-estate price database) with the parameters needed for a search. The site would then return an XML-formatted document with the resulting data (prices, location, features, etc). Because the data is returned in a standardized machine-parseable format, it could then be integrated directly into a third-party web site or application.

The SOAP architecture consists of several layers of specifications for message format, message exchange patterns (MEP), underlying transport protocol bindings, message processing models, and protocol extensibility. SOAP is the successor of XML-RPC, though it borrows its transport and interaction neutrality and the envelope/header/body from elsewhere (probably from WDDX).