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>