The main concept of Web Services is to exchange data between two devices using standardized protocols and messages.

What is Web Service and WSDL?

The W3C defines a Web services: a software system designed to support machine-to-machine interaction over network. Other systems interact with the Web service using SOAP messages, REST, or using HTTP with an XML serialization with other Web-related standards.

And for be little clear about WSDL (Web Services Description Language) - describes services as collection of network endpoints or ports in XML format.

Exchange messages usually accomplished by protocol HTTP. However, it should be noted that it is still used, but very rarely, protocol - SMTP (Simple Mail Transfer Protocol).

SOAP protocol

Protocol SOAP transfers messages or small amount of information. SOAP messages formatted in XML and are typically send using HTTP. Some time ago SOAP was spelled as Simply Object Access Protocol. But time passed and everybody saws that protocol isn’t simple and nothingness in common with access to objects.

Example of SOAP envelope

The SOAP message has 3 parts: envelope, head, body. Body contains all response/request data. Also can say that head isn’t required and in modern apps doesn’t used.

Example of SOAP XML:

<?xml version="1.0" encoding="utf-8" ?>
<soapenv:Envelope
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema"
    xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:urn="urn:WebservicesName"> <!-- service name -->
    <soap:Header>
        <m:Trans xmlns:m="http://schemas.xmlsoap.org/soap/encoding/">Header</m:Trans>
        </soap:Header>
    <soapenv:Body>
        <!-- method name -->
        <urn:ProductService.getProductByHash
            soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
            <!-- request to server -->
            <return xsi:type="getProductByHash ">
                <product_hash xsi:type="xsd:string">product hash here!</product_hash>
            </return>
        </urn:ProductService.getProductByHash>
    </soapenv:Body>
</soapenv:Envelope>

What here have happened? In the beginning I created SOAP envelope, which call service with URN (Uniform Resource Name). Then calling method getProductByHash.

SOAP response of web-service have next view, only body tag:

<soapenv:Body>
    <urn:ProductService.getProductByHash
        soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
        <return xsi:type="getProductByHash ">.
          <!-- response example -->
            <product_id xsi:type="xsd:string">260891</emag_id>
        </return>
    </urn:ProductService.getProductByHash>
</soapenv:Body>

#Create/receive SOAP request/response via $.soap

This script uses $.ajax to send a SOAP envelope. It can take XML DOM, XML string or JSON as input and the response can be returned as either XML DOM, XML string or JSON too.

Example:

$.soap({
    url: 'http://my.server.com/soapservices/',
    method: 'helloWorld',

    data: {
        name: 'Remy Blom',
        msg: 'Hi!'
    },

    success: function (soapResponse) {
        // do stuff with soapResponse
        // if you want to have the response as JSON use soapResponse.toJSON();
        // or soapResponse.toString() to get XML string
        // or soapResponse.toXML() to get XML DOM
    },
    error: function (SOAPResponse) {
        // show error
    }
})

Full $.soap documentation.