SOAP Simple Object Access Protocol

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SOAP(Simple Object Access Protocol)

• Matt Brodie
• March 20th 2006

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• "To help developers build Web services and
  link heterogeneous components over the Internet,
  Microsoft worked with industry experts to create
  the Simple Object Access Protocol. SOAP provides
  an open, extensible way for applications to
  communicate using XML-based messages over the
  Web, regardless of what operating system, object
  model or language particular applications may
  use. SOAP facilitates universal communication by
  defining a simple, extensible message format in
  standard XML and thereby providing a way to send
  that XML message over HTTP. Microsoft is
  soliciting industry feedback on version 0.9 of
  the SOAP specification. . ." MS announcement,
  Sept 13 1999"

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SOAPs designers

• Initial development done by a team including
  representatives from
• DevelopMentor
• IBM
• Lotus
• Microsoft
• UserLand

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SOAPs maintenance

• Currently under the auspices of the W3C XML
  Protocol Working Group, which includes
  representatives of
• BEA Systems
• IBM
• Microsoft
• Sun Microsystems
• Systinet
• Not to mention ATT, DaimlerChrysler, Intel, and
  Fujitsu

5
some definitions

• "SOAP is a protocol specification for invoking
  methods on servers, services, components and
  objects. SOAP codifies the existing practice of
  using XML and HTTP as a method invocation
  mechanism. The SOAP specification mandates a
  small number of HTTP headers that facilitate
  firewall/proxy filtering. The SOAP specification
  also mandates an XML vocabulary that is used for
  representing method parameters, return values,
  and exceptions." DevelopMentor

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continued

• The Simple Object Access Protocol (SOAP)
  facilitates interoperability among a wide range
  of programs and platforms, making existing
  applications accessible to a broader range of
  users. SOAP combines the proven Web technology
  of HTTP with the flexibility and extensibility of
  XML. perfectxml.com

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from the original MS press release

• SOAP provides an open, extensible way for
  applications to communicate using XML-based
  messages over the Web, regardless of what
  operating system, object model or language
  particular applications may use. SOAP facilitates
  universal communication by defining a simple,
  extensible message format in standard XML and
  thereby providing a way to send that XML message
  over HTTP. Microsoft

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the official definition

• SOAP is a lightweight protocol intended for
  exchanging structured information in a
  decentralized, distributed environment. SOAP uses
  XML technologies to define an extensible
  messaging framework, which provides a message
  construct that can be exchanged over a variety of
  underlying protocols. The framework has been
  designed to be independent of any particular
  programming model and other implementation
  specific semantics. W3C

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repetitious words

• Extensible
• Platform-nonspecific
• Utilizes existing software
• Facilitates communication
• Simple

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a bit of history

• Sometime in 1999 idea created, work started
• May 8, 2000 submitted to W3C
• June 24, 2003 published as a W3C recommendation
• Now, development is focused on common suite of
  SOAP extensions to add reliability, security,
  etc.
• Global XML Web Services Architecture (GXA)

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SOAPs predecessors

• DCOM and CORBA
• Remote Procedure Call (RCP) Protocols
• Poorly designed for Web Services
• Initially, SOAP was designed to make DCOM and
  CORBA work over the internet.

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simple depiction of SOAP in action
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SOAP

• is a format for one-way communication
• describes how a message should be transported
  through the web
• governs which portions of the document should be
  read and by whom
• is a format describing how the client turns the
  message into an RPC call and converts it into a
  SOAP reply

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SOAP message structure

• HTTP binding
• directs the message
• Envelope
• always the root element, it helps the server
  identify the message as SOAP, and it is defined
  by its own schema SOAP-ENV
• Header (optional)
• specifying use
• Adds features to the SOAP message such as
  authentication, transaction management, payment,
  message routes, etc
• Body
• containing the payload

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very simple example
ltEnvelopegt ltHeadergt lttransIdgt345lt/transId
gt lt/Headergt ltBodygt ltAddgt
ltn1gt3lt/n1gt ltn2gt4lt/n2gt lt/Addgt
lt/Bodygt lt/Envelopegt
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HTTP binding

• directs SOAP message across HTTP
• always a POST format
• content-type is always text/xml
• includes the special header SOAPAction
• this is not mandatory, supposed to express the
  function of the message

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HTTP binding for a request POST
/string_server/Object17 HTTP/1.1 Host
209.110.197.2 Content-Type text/xml Content-Lengt
h nnn
Response 200 OK Content-Type text/xml Content-Le
ngth nnn
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previous example, fleshed out
ltSOAP-ENVEnvelope xmlnsSOAP-ENVhttp//sche
mas.xmlsoap.org/soap/envelope/
SOAP-ENVencodingStyle"http//schemas.xmlsoap.org
/soap/encoding/gt ltSOAP-ENVHeadergt
ltttransId xmlnsthttp//a.com/transgt345lt/ttra
nsIdgt lt/SOAP-ENVHeadergt ltSOAP-ENVBodygt
ltmAdd xmlnsmhttp//a.com/Calculatorgt
ltn1gt3lt/n1gt ltn2gt4lt/n2gt
lt/mAddgt lt/SOAP-ENVBodygt lt/SOAP-ENVEnvelopegt
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intermediaries

• intermediaries act as soap receivers and senders
• they often process messages and send them on
• the SOAP message is encoded with instructions for
  the receiver will deal with the message
• it may ignore certain sections of the body, if it
  is told to in the header

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drawbacks

• dozens of SOAP toolkits being used to build, many
  interpret message differently
• SOAP is very ambiguous, no data encoding format
• Just because the server is using SOAP doesnt
  mean its encoding in the way you expect it to
• The rules governing encoding within the envelope
  are known as Section 5 rules
• these rules are not required, causing problems
  when users make assumptions about their use

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SOAP message example
POST /StockQuote HTTP/1.1 Host
www.stockquoteserver.com Content-Type text/xml
charset"utf-8" Content-Length nnnn SOAPAction
"Some-URI" ltSOAP-ENVEnvelope
xmlnsSOAP-ENV"http//schemas.xmlsoap.org/soap/en
velope/" SOAP-ENVencodingStyle"http//schemas.
xmlsoap.org/soap/encoding/"gt ltSOAP-ENVBodygt
ltmGetLastTradePrice xmlnsm"Some-URI"gt
ltsymbolgtDISlt/symbolgt
lt/mGetLastTradePricegt lt/SOAP-ENVBodygt lt/SOAP-
ENVEnvelopegt
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example response
HTTP/1.1 200 OK Content-Type text/xml
charset"utf-8" Content-Length
nnnn ltSOAP-ENVEnvelope xmlnsSOAP-ENV"http//
schemas.xmlsoap.org/soap/envelope/"
SOAP-ENVencodingStyle"http//schemas.xmlsoap.org
/soap/encoding/"/gt ltSOAP-ENVBodygt
ltmGetLastTradePriceResponse xmlnsm"Some-URI"gt
ltPricegt34.5lt/Pricegt
lt/mGetLastTradePriceResponsegt
lt/SOAP-ENVBodygt lt/SOAP-ENVEnvelopegt