SOAP
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- This article is about a computer protocol. For the common cleaning mixture, see soap. For other uses of the acronym SOAP, see soap (disambiguation).
SOAP is a standard for exchanging XML-based messages over a computer network, normally using HTTP. SOAP forms the foundation layer of the web services stack, providing a basic messaging framework that more abstract layers can build on.
There are several different types of messaging patterns in SOAP, but by far the most common is the Remote Procedure Call (RPC) pattern, where one network node (the client) sends a request message to another node (the server), and the server immediately sends a response message to the client.
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Overview
SOAP originally was an acronym for Simple Object Access Protocol, but the acronym was dropped in Version 1.2 of the SOAP specification. Originally designed by Dave Winer, Don Box, Bob Atkinson, and Mohsen Al-Ghosein in 1998 with backing from Microsoft (where Atkinson and Al-Ghosein worked at the time), the SOAP specification is currently maintained by the XML Protocol Working Group of the World Wide Web Consortium.
Transport methods
HTTP was chosen as the primary application layer protocol for SOAP since it works well with today's Internet infrastructure, specifically, SOAP works well with network firewalls. This is a major advantage over other distributed protocols like GIOP/IIOP or DCOM which are normally filtered by firewalls.
XML was chosen as the standard message format because of its widespread acceptance by major corporations and open source development efforts. Additionally, a wide variety of freely available tools significantly ease the transition to a SOAP-based implementation.
The somewhat lengthy syntax of XML can be both a benefit and a drawback. Its format is easy for humans to read, but can be complex and slow down processing times. For example, GIOP and DCOM use much shorter, binary message formats. On the other hand, hardware appliances are available to accelerate processing of XML messages. Binary XML (the use of the word "XML" is controversial here) is also being explored as a means for streamlining the throughput requirements of XML.
Structure of a SOAP message
A SOAP message is contained in an envelope. Within this envelope are two additional sections: the header and the body of the message. SOAP messages use XML namespaces.
The header contains relevant information about the message. For example, a header can contain the date the message is sent, or authentication information. It is not required, but must always be included at the top of the envelope when it is present.
Example SOAP messages
Here is an example of how a client might format a SOAP message requesting product information from a fictional warehouse web service. The client needs to know which product corresponds with the ID 827635:
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<getProductDetails xmlns="http://warehouse.example.com/ws">
<productID>827635</productID>
</getProductDetails>
</soap:Body>
</soap:Envelope>
Here is how the warehouse web service might format its reply message with the requested product information:
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<getProductDetailsResponse xmlns="http://warehouse.example.com/ws">
<getProductDetailsResult>
<productName>Toptimate 3-Piece Set</productName>
<productID>827635</productID>
<description>3-Piece luggage set. Black Polyester.</description>
<price>96.50</price>
<inStock>true</inStock>
</getProductDetailsResult>
</getProductDetailsResponse>
</soap:Body>
</soap:Envelope>
See also
Related technologies
- Comparison of Web service markup languages
- List of Web service markup languages
- Component technologies
- Web service and some of its core technologies WSDL, UDDI
- WS-I Basic Profile
Alternatives to SOAP
- Burlap [1] (http://www.caucho.com/burlap/)
- GXA
- Hessian Web Service Protocol [2] (http://www.caucho.com/hessian/index.xtp)
- REST
- XML-RPC
External links
- Dave Winer's history of SOAP (http://www.xmlrpc.com/stories/storyReader$555)
- Discussion on Web Services technology (SOAP and REST) (http://www.advogato.org/article/464.html)
- Don Box's history of SOAP (http://webservices.xml.com/pub/a/ws/2001/04/04/soap.html)
- Perl SOAP Module (http://www.soaplite.com/)
- Category at ODP (http://dmoz.org/Computers/Programming/Internet/Web_Services/SOAP)
- Technology Report (http://xml.coverpages.org/soap.html)
- Two-way SOAP to CORBA bridge (http://soap2corba.sourceforge.net/)
- What is SOAP? (http://searchwebservices.techtarget.com/searchWebServices/downloads/what_is_soap.swf) (Flash presentation; requires plugin.)
- W3C School SOAP Tutorial (http://www.w3schools.com/soap/)
- W3C SOAP primer (http://www.w3.org/TR/soap12-part0/)
- XML protocol activity (http://www.w3.org/2000/xp/)de:Simple Object Access Protocol
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