SOAP - SOAP Encoding

1. What is SOAP Encoding?

• SOAP encoding is a set of rules that describe how data types are represented in XML within a SOAP message.

• Defined in the SOAP specification under the namespace:

http://schemas.xmlsoap.org/soap/encoding/

• It tells the sender and receiver how to serialize (encode) or deserialize (decode) data like integers, strings, arrays, objects, etc., into XML format.

2. Why is SOAP Encoding Needed?

• Different programming languages represent data types differently.

• SOAP encoding provides a standard way to represent complex data types in XML so that:

  • A Java program can send data to a .NET program.

  • A Python client can understand a C++ server’s response.

3. SOAP Encoding Styles

There are two common encoding styles:

1. Literal Encoding (document/literal)

   • The XML message directly matches the schema (no extra encoding rules).

   • Most common and widely used today.

2. SOAP Encoding (RPC/encoded)

   • Uses the SOAP encoding rules to represent parameters in an RPC (Remote Procedure Call) style.

   • Was common in early SOAP services but now less popular.

4. Example: SOAP Encoding in Use

Suppose we want to send an array of integers [10, 20, 30].

SOAP Request with Encoding

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
               soap:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
   <soap:Body>
      <ns1:getNumbers xmlns:ns1="http://example.com/">
         <numbers soapenc:arrayType="xsd:int[3]" 
                  xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/"
                  xmlns:xsd="http://www.w3.org/2001/XMLSchema">
            <number>10</number>
            <number>20</number>
            <number>30</number>
         </numbers>
      </ns1:getNumbers>
   </soap:Body>
</soap:Envelope>

Explanation:

• soap:encodingStyle → specifies encoding rules being used.

• xsd:int → defines the data type (integer).

• soapenc:arrayType="xsd:int[3]" → tells the receiver it’s an array of 3 integers.

5. Key Points about SOAP Encoding

1. SOAP encoding defines serialization rules for data types in XML.

2. Declared using the attribute:

   soap:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
   

3. Handles simple types (int, string, boolean) and complex types (arrays, objects).

4. Literal encoding is more widely used today (especially with WSDL + Document/Literal style).

5. RPC/encoded style is now less common, but still important to understand for legacy systems.