Types of web services

There are many types of web services that have evolved over time. Some of the more prominent ones are as follows:

• Simple Object Access Protocol (SOAP)
• Universal Description, Discovery, and Integration (UDDI)

• Web Services Description Language (WSDL)
• Representational State Transfer (REST)

Out of these, SOAP became popular in the early 2000s, when XML riding on a high wave. The XML data format is used by various distributed systems to communicate with each other.

A SOAP request usually consists of these three basic components:

• The envelope
• The header
• The body

Just to perform an HTTP request and response cycle, we have to attach a lot of additional data in SOAP. A sample SOAP request to a fictional book server, www.example.org, looks like this:

POST /Books HTTP/1.1
Host: www.example.org
Content-Type: application/soap+xml; charset=utf-8
Content-Length: 299
SOAPAction: "https://www.w3.org/2003/05/soap-envelope"

<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope" xmlns:m="https://www.example.org">
  <soap:Header>
  </soap:Header>
  <soap:Body>
    <m:GetBook>
      <m:BookName>Alice in the wonderland</m:BookName>
    </m:GetBook>
  </soap:Body>
</soap:Envelope>

This is a standard example of a SOAP request for getting book data. If we observe carefully, it is in XML format, with special tags specifying the envelope and body. Since XML works by defining a lot of namespaces, the response gets bulky.

The main drawback of SOAP is that it is too complex for implementing web services and is a heavyweight framework. A SOAP HTTP request can get very bulky and can cause bandwidth wastage. The experts looked for a simple alternative, and in came REST. In the next section, we will briefly discuss REST.