WSDL Notes from W3C Spec

1. WSDL is an XML format for describing network services as a set of endpoints operating on messages containing either document-oriented or procedure-oriented information.


2. Elements in WSDL:
   
   
   
   1. Types - a container for data type definitions using some type system (such as XSD).
   
   
   2. Message – an abstract, typed definition of the data being communicated.
   
   
   3. Operation – an abstract description of an action supported by the service.
   
   
   4. Port Type – an abstract set of operations supported by one or more endpoints.
   
   
   5. Binding – a concrete protocol and data format specification for a particular port type.
   
   
   6. Port – a single endpoint defined as a combination of a binding and a network address.
   
   
   7. Service – a collection of related endpoints.
   
   
   
   


3. WSDL doesn't introduce a type definition language. Supports XSD as canonical type system. Allows using other type definition languages via extensibility.


4. Binding mechanism is used to attach a specific protocol or data format or structure to an abstract message or operation or end point.


5. It introduces specific binding extensions for the following protocols and message format : SOAP 1.1, HTTP GET/POST, MIME. Other binding extensions can also be used.


6. Message definitions are always considered to be an abstract definition of the message content. A message binding describes how the abstract content is mapped into a concrete format.


7. WSDL has four transmission primitives that an endpoint can support:
   
   
   
   1. One-Way:endpoint receives a message.
   
   
   2. Request-Response:endpoint receives a message, and sends a correlated message.
   
   
   3. Solicit-Response :endpoint sends a message, and receives a correlated message.
   
   
   4. Notification : endpoint sends a message.
   
   
   
   


8. There may be any number of binding for a port type. A Binding must specify exactly one protocol. Binding must not specify address information.


9. A port must not specify more than one address. It must not specify any binding information other than address information.


10. Ports within service have the following relationship:
    
    
    
    1. None of the ports communicate with each other (e.g. the output of one port is not the input of another).
    
    
    2. If a service has several ports that share a port type, but employ different bindings or addresses, the ports are alternatives. This allows a consumer of a WSDL document to choose particular port(s) to communicate with based on some criteria (protocol, distance, etc.).
    
    
    
    


11. SOAP Binding extends WSDL with the following extension elements:
    
    
    
    1. soap:binding - Signify that the binding is bound to the SOAP protocol format: Envelop, header and body. URI for the transport attribute of this element signifies which transport of SOAP. Can be HTTP, SMTP, FTP etc.,
    
    
    2. soap:operation - Required for the HTTP protocol binding of SOAP. For other SOAP protocol bindings, soap:action attribute must not be specified and this attribute may be omitted.
    
    
    3. soap:body - specifies how message parts appear inside soap body element. May be abstract schema defintiions or concrete. If abstract, then serialized according to some encoding style. The soap:body element is used in both RPC-oriented and document-oriented messages, but the style of the enclosing operation has important effects on how the Body section is structured:
       
       
       
       1. If the operation style is rpc each part is a parameter or a return value and appears inside a wrapper element within the body
       
       
       2. If the operation style is document there are no additional wrappers, and the message parts appear directly under the SOAP Body element.
       
       
       
       
    
    
    4. soap:address - The SOAP address binding is used to give a port an address (a URI). The URI scheme specified for the address must correspond to the transport specified by the soap:binding.
    
    
    
    

SOAP Message Embedded in HTTP Request

POST /StockQuote HTTP/1.1 
Host: www.stockquoteserver.com 
Content-Type: text/xml; charset="utf-8" 
Content-Length: nnnn 
SOAPAction: "Some-URI"  

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org

/soap/envelope/"> 
    <soapenv:Body> 
        <m:GetLastTradePrice xmlns:m="Some-URI"> 
            <m:tickerSymbol>DIS</m:tickerSymbol> 
        </m:GetLastTradePrice> 
    </soapenv:Body> 
</soapenv:Envelope>

SOAP Message Embedded in HTTP Response

HTTP/1.1 200 OK 
Content-Type: text/xml; charset="utf-8" 
Content-Length: nnnn  

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org

/soap/envelope/"> 
    <soapenv:Body> 
        <m:GetLastTradePriceResponse xmlns:m="Some-URI"> 
            <m:price>34.5</m:price> 
        </m:GetLastTradePriceResponse> 
    </soapenv:Body> 
</soapenv:Envelope>