SOAP

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This article is about the computer protocol. For the common cleaning mixture, see Soap. For other uses, see Soap (disambiguation).

SOAP (originally Simple Object Access Protocol lately also Service Oriented Architecture Protocol) is a protocol for exchanging XML-based messages over computer networks, 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. The original acronym was dropped with Version 1.2 of the standard, which became a W3C Recommendation on June 24, 2003, as it was considered to be misleading. [1]

There are several different types of messaging patterns in SOAP, but by far the most common is the Remote Procedure Call (RPC) pattern, in which 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. 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[citation needed].

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) as an object-access protocol, the SOAP specification is currently maintained by the XML Protocol Working Group of the World Wide Web Consortium.

Contents

[edit] Transport methods

SOAP makes use of an Internet application layer protocol as a transport protocol. Critics have argued that this is an abuse of such protocols, as it is not their intended purpose and therefore not a role they fulfill well. Apologists for SOAP have drawn analogies to successful uses of protocols at various levels for tunneling other protocols.[citation needed]

Both SMTP and HTTP are valid application layer protocols for SOAP, but HTTP has gained wider acceptance as it works well with today's Internet infrastructure; specifically, SOAP works well with network firewalls. SOAP may also be used over HTTPS (since it is the same protocol as HTTP at the application level, but using an encrypted transport protocol underneath) in either simple or mutual authentication, this is the advocated WS-I method to provide web service security as stated in the WS-I Basic Profile 1.1, see [2]. 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 use 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 possible for humans to read, but can be complex and can have slow processing times. For example, CORBA, GIOP, ICE, and DCOM use much shorter, binary message formats. On the other hand, hardware appliances are available to accelerate processing of XML messages. [3][4]. Binary XML is also being explored as a means for streamlining the throughput requirements of XML.

[edit] Weaknesses

  • Because of the lengthy XML format, SOAP can be considerably slower than competing middleware technologies such as CORBA. This may not be an issue when only small messages are sent[5].
  • When relying on HTTP as a transport protocol and not using WS-Addressing or an ESB, the roles of the interacting parties are fixed. Only one party (the client) can use the services of the other. So developers must use polling instead of notification in these common cases.
  • Many SOAP implementations limit the amount of data that can be sent.
  • Most uses of HTTP as a transport protocol are done in ignorance of how the operation would be modelled in HTTP. This agnosticism is by design (with analogy to how different protocols sit on top of each other in the IP stack) but the analogy is imperfect (because the application protocols used as transport protocols are not really transport protocols). Because of this there is no way to know if the method used is appropriate to the operation. This makes good analysis of the operation at the application-protocol level problematic at best with results that are at least sub-optimal (if the POST-based binding is used for an application which in HTTP would be more naturally modelled as a GET operation), and which may be buggy (if for example the GET based binding were used for an operation which did not have the idempotency required of GET).

[edit] Example

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>

And here is a possible response to the client request:

 <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 currency="NIS">96.50</price>
         <inStock>true</inStock>
       </getProductDetailsResult>
     </getProductDetailsResponse>
   </soap:Body>
 </soap:Envelope>

[edit] See also

[edit] Related technologies

[edit] Alternatives to SOAP

[edit] External links

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