Difference between a SOAP message and a WSDL

Question

I am confused about how SOAP messages and WSDL fit together   I have started looking into SOAP messages such as       POST  InStock HTTP 1 1 Host  www example org Content-Type  application soap xml  charset utf-8 Content-Length  nnn   lt  xml version  1 0   gt   lt soap Envelope xmlns soap  http   www w3 org 2001 12 soap-envelope  soap encodingStyle  http   www w3 org 2001 12 soap-encoding  gt    lt soap Body xmlns m  http   www example org stock  gt     lt m GetStockPrice gt       lt m StockName gt IBM lt  m StockName gt     lt  m GetStockPrice gt   lt  soap Body gt    lt  soap Envelope gt    Are all SOAP messages WSDL s  Is SOAP a protocol that accepts its own  SOAP messages  or  WSDL s   If they are different   then when should I use SOAP messages and when should I use WSDL s   Some clarification around this would be awesome

User · Answer

The WSDL is a kind of contract between API provider and the client it's describe the web service : the public function , optional/required field ...

But The soap message is a data transferred between client and provider (payload)

User · Answer

A WSDL  Web Service Definition Language  is a meta-data file that describes the web service   Things like operation name  parameters etc   The soap messages are the actual payloads

User · Answer

In a simple terms if you have a web service of calculator  WSDL tells about the functions that you can implement or exposed to the client  For example  add  delete  subtract and so on  Where as using SOAP you actually perform actions like doDelete    doSubtract    doAdd    So SOAP and WSDL are apples and oranges  We should not compare them  They both have their own different functionality

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A SOAP message is a XML document which is used to transmit your data  WSDL is an XML document which describes how to connect and make requests to your web service    Basically SOAP messages are the data you transmit  WSDL tells you what you can do and how to make the calls   A quick search in Google will yield many sources for additional reading  previous book link now dead  to combat this will put any new recommendations in comments   Just noting your specific questions   Are all SOAP messages WSDL s  No  they are not the same thing at all   Is SOAP a protocol that accepts its own  SOAP messages  or  WSDL s  No - reading required as this is far off   If they are different  then when should I use SOAP messages and when should I use WSDL s  Soap is structure you apply to your message data for transfer  WSDLs are used only to determine how to make calls to the service in the first place  Often this is a one time thing when you first add code to make a call to a particular webservice

User · Answer

SOAP    It s an open standard XML based Communication protocol which is used to exchange information from the user to web service or vice versa   The soap is just the document in which the data are organized in some Manner   For every request and response separate soap may be present   WSDL   In soap the data are organized in some manner and this organization is specified in WSDL  The data type which has to be used are also specified here   For request and response single WSDL will be present

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WSDL act as an interface between sender and receiver  SOAP message is request and response in xml format   comparing with java RMI  WSDL is the interface class SOAP message is marshaled request and response message

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We can consider a telephone call In that Number is wsdl and exchange of information is soap   WSDL is description how to connect with communication server SOAP is have communication messages

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Better analogy than the telephone call   Ordering products via postal mail from a mail-order service  The WSDL document is like the instructions that explain how to create the kind of order forms that the service provider will accept  A SOAP message is like an envelope with a standard design  size  shape  construction  that every post office around the world knows how to handle  You put your order form into such an envelope   The network  e g  the internet  is the postal service   You put your envelope into the mail   The employees of the postal service do not look inside the envelope  The payload XML is the order form that you have enclosed in the envelope  After the post office delivers the envelope  the web service provider opens the envelope and processes the order form   If you have created and filled out the form correctly  they will mail the product that you ordered back to you

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We need to define what is a web service before telling what are the difference between the SOAP and WSDL where the two  SOAP and WSDL  are components of a web service  Most applications are developed to interact with users  the user enters or searches for data through an interface and the application then responds to the user s input   A Web service does more or less the same thing except that a Web service application communicates only from machine to machine or application to application  There is often no direct user interaction   A Web service basically is a collection of open protocols that is used to exchange data between applications  The use of open protocols enables Web services to be platform independent  Software that are written in different programming languages and that run on different platforms can use Web services to exchange data over computer networks such as the Internet  In other words  Windows applications can talk to PHP  Java and Perl applications and many others  which in normal circumstances would not be possible      How Do Web Services Work    Because different applications are written in different programming languages  they often cannot communicate with each other  A Web service enables this communication by using a combination of open protocols and standards  chiefly XML  SOAP and WSDL  A Web service uses XML to tag data  SOAP to transfer a message and finally WSDL to describe the availability of services  Let s take a look at these three main components of a Web service application   Simple Object Access Protocol  SOAP   The Simple Object Access Protocol or SOAP is a protocol for sending and receiving messages between applications without confronting interoperability issues  interoperability meaning the platform that a Web service is running on becomes irrelevant   Another protocol that has a similar function is HTTP  It is used to access Web pages or to surf the Net  HTTP ensures that you do not have to worry about what kind of Web server -- whether Apache or IIS or any other -- serves you the pages you are viewing or whether the pages you view were created in ASP NET or HTML   Because SOAP is used both for requesting and responding  its contents vary slightly depending on its purpose   Below is an example of a SOAP request and response message  SOAP Request   POST  InStock HTTP 1 1  Host  www bookshop org  Content-Type  application soap xml  charset utf-8  Content-Length  nnn   lt  xml version  1 0   gt    lt soap Envelope  xmlns soap  http   www w3 org 2001 12 soap-envelope   soap encodingStyle  http   www w3 org 2001 12 soap-encoding  gt    lt soap Body xmlns m  http   www bookshop org prices  gt        lt m GetBookPrice gt        lt m BookName gt The Fleamarket lt  m BookName gt        lt  m GetBookPrice gt    lt  soap Body gt    lt  soap Envelope gt    SOAP Response   POST  InStock HTTP 1 1  Host  www bookshop org  Content-Type  application soap xml  charset utf-8  Content-Length  nnn   lt  xml version  1 0   gt    lt soap Envelope  xmlns soap  http   www w3 org 2001 12 soap-envelope   soap encodingStyle  http   www w3 org 2001 12 soap-encoding  gt    lt soap Body xmlns m  http   www bookshop org prices  gt        lt m GetBookPriceResponse gt        lt m  Price gt 10 95 lt  m  Price gt        lt  m GetBookPriceResponse gt    lt  soap Body gt    lt  soap Envelope gt     Although both messages look the same  they carry out different methods  For instance looking at the above examples you can see that the requesting message uses the GetBookPrice method to get the book price  The response is carried out by the GetBookPriceResponse method  which is going to be the message that you as the  requestor  will see  You can also see that the messages are composed using XML   Web Services Description Language or WSDL  WSDL is a document that describes a Web service and also tells you how to access and use its methods   WSDL takes care of how do you know what methods are available in a Web service that you stumble across on the Internet   Take a look at a sample WSDL file    lt  xml version  1 0  encoding  UTF-8   gt    lt definitions  name   DayOfWeek      targetNamespace  http   www roguewave com soapworx examples DayOfWeek wsdl     xmlns tns  http   www roguewave com soapworx examples DayOfWeek wsdl     xmlns soap  http   schemas xmlsoap org wsdl soap       xmlns xsd  http   www w3 org 2001 XMLSchema     xmlns  http   schemas xmlsoap org wsdl   gt       lt message name  DayOfWeekInput  gt        lt part name  date  type  xsd date   gt      lt  message gt      lt message name  DayOfWeekResponse  gt        lt part name  dayOfWeek  type  xsd string   gt      lt  message gt      lt portType name  DayOfWeekPortType  gt        lt operation name  GetDayOfWeek  gt          lt input message  tns DayOfWeekInput   gt          lt output message  tns DayOfWeekResponse   gt        lt  operation gt      lt  portType gt      lt binding name  DayOfWeekBinding  type  tns DayOfWeekPortType  gt        lt soap binding style  document          transport  http   schemas xmlsoap org soap http   gt        lt operation name  GetDayOfWeek  gt          lt soap operation soapAction  getdayofweek   gt          lt input gt            lt soap body use  encoded              namespace  http   www roguewave com soapworx examples              encodingStyle  http   schemas xmlsoap org soap encoding    gt          lt  input gt          lt output gt            lt soap body use  encoded              namespace  http   www roguewave com soapworx examples                 encodingStyle  http   schemas xmlsoap org soap encoding    gt          lt  output gt        lt  operation gt      lt  binding gt      lt service name  DayOfWeekService   gt        lt documentation gt         Returns the day-of-week name for a given date       lt  documentation gt        lt port name  DayOfWeekPort  binding  tns DayOfWeekBinding  gt          lt soap address location  http   localhost 8090 dayofweek DayOfWeek   gt        lt  port gt      lt  service gt    lt  definitions gt     The main things to remember about a WSDL file are that it provides you with   A description of a Web service  The methods a Web service uses and the parameters that it takes  A way to locate Web services

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A SOAP document is sent per request  Say we were a book store  and had a remote server we queried to learn the current price of a particular book  Say we needed to pass the Book s title  number of pages and ISBN number to the server   Whenever we wanted to know the price  we d send a unique SOAP message  It d look something like this     lt SOAP-ENV Envelope   xmlns SOAP-ENV  http   schemas xmlsoap org soap envelope     SOAP-ENV encodingStyle  http   schemas xmlsoap org soap encoding   gt     lt SOAP-ENV Body gt       lt m GetBookPrice xmlns m  http   namespaces my-example-book-info com  gt         lt ISBN gt 978-0451524935 lt  ISBN gt         lt Title gt 1984 lt  Title gt         lt NumPages gt 328 lt  NumPages gt       lt  m GetBookPrice gt     lt  SOAP-ENV Body gt   lt  SOAP-ENV Envelope gt     And we expect to get a SOAP response message back like    lt SOAP-ENV Envelope   xmlns SOAP-ENV  http   schemas xmlsoap org soap envelope     SOAP-ENV encodingStyle  http   schemas xmlsoap org soap encoding   gt     lt SOAP-ENV Body gt       lt m GetBookPriceResponse xmlns m  http   namespaces my-example-book-info com  gt         lt CurrentPrice gt 8 99 lt  CurrentPrice gt         lt Currency gt USD lt  Currency gt       lt  m GetBookPriceResponse gt     lt  SOAP-ENV Body gt   lt  SOAP-ENV Envelope gt    The WSDL then describes how to handle process this message when a server receives it  In our case  it describes what types the Title  NumPages  amp  ISBN would be  whether we should expect a response from the GetBookPrice message and what that response should look like    The types would look like this     lt wsdl types gt      lt  -- all type declarations are in a chunk of xsd -- gt     lt xsd schema targetNamespace  http   namespaces my-example-book-info com      xmlns xsd  http   www w3 org 1999 XMLSchema  gt        lt xsd element name  GetBookPrice  gt         lt xsd complexType gt           lt xsd sequence gt             lt xsd element name  ISBN  type  string   gt             lt xsd element name  Title  type  string   gt             lt xsd element name  NumPages  type  integer   gt           lt  xsd sequence gt         lt  xsd complexType gt       lt  xsd element gt        lt xsd element name  GetBookPriceResponse  gt         lt xsd complexType gt           lt xsd sequence gt             lt xsd element name  CurrentPrice  type  decimal    gt             lt xsd element name  Currency  type  string    gt           lt  xsd sequence gt         lt  xsd complexType gt       lt  xsd element gt      lt  xsd schema gt   lt  wsdl types gt    But the WSDL also contains more information  about which functions link together to make operations  and what operations are avaliable in the service  and whereabouts on a network you can access the service operations   See also W3 Annotated WSDL Examples

[java] Difference between a SOAP message and a WSDL?

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