Introduction To Web Services

What are Web Services?

Web services are a standardized way of integrating web-based applications using open standards such as HTML, XML, WSDL, and SOAP. Web services allow different applications from different sources to communicate with each other without time-consuming custom coding, and because all communication is in XML, web services are not tied to any one operating system or programming language.

Types of Web Services

There are mainly two types of web services:

SOAP Web Services
RESTful Web Services

SOAP Web Services

SOAP (Simple Object Access Protocol) is a protocol for exchanging structured information in the implementation of web services in computer networks. It relies on XML Information Set for its message format, and usually relies on other application layer protocols, most notably HTTP and SMTP, for message negotiation and transmission.

Example SOAP Request:

POST /StockQuote HTTP/1.1
Host: www.example.org
Content-Type: text/xml; charset=utf-8
Content-Length: nnnn
SOAPAction: "http://www.example.org/StockQuote"

<?xml version="1.0"?>
<soap:Envelope
    xmlns:soap="http://www.w3.org/2003/05/soap-envelope"
    soap:encodingStyle="http://www.w3.org/2003/05/soap-encoding">
  <soap:Body xmlns:m="http://www.example.org/stock">
    <m:GetStockQuote>
      <m:StockName>IBM</m:StockName>
    </m:GetStockQuote>
  </soap:Body>
</soap:Envelope>

RESTful Web Services

REST (Representational State Transfer) is an architectural style that defines a set of constraints to be used for creating web services. Web services that conform to the REST architectural style, called RESTful web services, provide interoperability between computer systems on the internet. RESTful web services allow the requesting systems to access and manipulate textual representations of web resources using a uniform and predefined set of stateless operations.

Example RESTful Request:

GET /users/123 HTTP/1.1
Host: www.example.org
Accept: application/json

Creating a Simple RESTful Web Service in PHP

Let's create a simple RESTful web service in PHP. This service will have a single endpoint that returns a JSON representation of a user.

Example PHP Code:

<?php
header("Content-Type: application/json");

$response = array(
    "id" => 123,
    "name" => "John Doe",
    "email" => "john.doe@example.org"
);

echo json_encode($response);
?>

When you access this PHP script from your browser or a HTTP client, you will get the following JSON response:

{ "id": 123, "name": "John Doe", "email": "john.doe@example.org" }

Conclusion