 by Thomas Erl |
XML Core Technology |
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SOAP in a Nutshell |
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| The Simple Object Access Protocol (SOAP) is a technology based on XML and HTTP that supports and extends interoperability between Web applications by providing a platform and vendor independent method for inter-application communication, specifically, communication between application services. Traditionally this was accomplished through binary communication protocols, such as DCOM, which were originally designed for use in client-server environments. |
| Until now, one of the primary challenges encountered with integrating these binary protocols within Internet applications has been the requirement that firewalls open a separate port (in addition to the HTTP port) to allow external communication with application services. This raised both operational and security issues. SOAP addresses these concerns by allowing access to application services via HTTP. |
| Since SOAP is also vendor neutral, it aims to become a universal application services protocol, eliminating the need to choose a vendor-specific platform. This opens up many new interoperability opportunities which previously required “bridging” and “gateway” technologies. For instance, with SOAP as the chosen communications protocol, COM components can communicate directly with CORBA components. |
| It is worth noting, however, that the current SOAP specification does not provide some of the advanced features of binary communication technologies, such as automatic garbage collection, and the ability to group messages in batches. |
| As with standard inter-component communication, a message requesting the use of a service (component) must identify the service, method and parameters. A SOAP request message defines the target service in its header section (which is similar to standard HTTP header syntax), as follows: |
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POST /CheckBooks HTTP/1.1 Host: www.bookwarehouse.com Content-Type: text/xml; charset="utf-8" Content-Length: nnnn SOAPAction: www.soasystems.com The details of the service communication are established in the body of the SOAP message, known as the “envelope”, using XML syntax as follows: |
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<SOAP-ENV:Envelope xmlns:SOAP-ENV= "http://schemas.xmlsoap.org/soap/envelope/" SOAP-ENV:encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/"> <SOAP-ENV:Body> <m:CheckAvailability xmlns:m="www.soasystems.com"> <title> Lathering for Dummies </title> </m:CheckAvailability> </SOAP-ENV:Body> </SOAP-ENV:Envelope> |
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While SOAP messages can be transmitted just one way, a complete request/response model (called the “Message Exchange Model”) is provided allowing components to return results in response to a request. The headers of a typical (successful) SOAP response message would appear similar to the following: |
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HTTP/1.1 200 OK Content-Type: text/xml; charset="utf-8" Content-Length: nnnn The following envelope section of the SOAP response provides a return value: |
SOA: Principles of Service Design by Thomas Erl  An in-depth guide dedicated to service engineering with a thorough exploration of the design principles that comprise the service-orientation design paradigm (including a comparison with object-orientation). 
Service-Oriented Architecture:Concepts, Technology, and Design by Thomas Erl The first "how-to" guide to building SOA, providing coverage of WS-* specifications, .NET and J2EE platforms, and step-by-step processes for service-oriented analysis and design. 
Service-Oriented Architecture:A Field Guide to Integrating XML and Web Services by Thomas Erl The best-selling guide to service-oriented integration, providing hundreds of integration strategies and over sixty best practices. For more information about either book, visit: www.soabooks.com |
About SOA Systems
SOA Systems Inc. provides strategic SOA consulting services and offers a comprehensive SOA training program. For more information see: • www.soasystems.com • www.soatraining.com |
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<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" SOAP-ENV:encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/"/> <SOAP-ENV:Body> <m:CheckAvailabilityResponse xmlns:m="www.soasystems.com"> <Quantity> 12 </Quantity> </m:CheckAvailabilityResponse> </SOAP-ENV:Body> </SOAP-ENV:Envelope> |
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