# Introduction

Warning

This extension is EXPERIMENTAL. The behaviour of this extension including the names of its functions and any other documentation surrounding this extension may change without notice in a future release of PHP. This extension should be used at your own risk.

SCA for PHP makes it possible for a PHP programmer to write reusable components, which can be called in a variety of ways, with an identical interface and with a minimum of fuss. At present components can call each other either locally or via Web services, but in the future it is expected that other ways will be possible. It provides the programmer with a way of doing this which will look as natural as possible in PHP.

SCA components use phpDocumentor-style (see http://www.phpdoc.org/) annotations to declare dependencies on other SCA components or Web services. The SCA for PHP runtime resolves these dependencies at runtime on behalf of the components, and thus allows the PHP programmer to focus on the business logic rather than on locating and obtaining references to dependencies.

The SCA for PHP programming model can be extended to support a number of service types, such as REST and Atompub. However, Web services (more accurately, WSDL defined, SOAP/HTTP services), are the only type currently specified.

Components also use annotations to define the interface which they expose as a service. The SCA for PHP runtime will automatically generate WSDL from these annotations, so that an SCA component is easily exposed as a web service. These annotations are a natural extension to those provided by phpDocumentor. Deploying a Web service can be as simple as placing a PHP component under the document root of a web server.

Components also use annotations to specify data structures (expressed using XML schema complex types) which are then handled using Service Data Objects (SDOs).

A PHP script which is not an SCA component and which contains no annotations can use the services of an SCA component. A PHP script or component can make calls to a web service that is not an SCA component, but using the same system of calls or annotations to obtain a reference.

First we show a single SCA component, ConvertedStockQuote which illustrates many of the features of SCA for PHP. It has one method, getQuote(), which given a stock "ticker" obtains a price quote for that stock, converted to a given currency. We shall be using this example as a basis for explaining the SCA for PHP throughout the rest of this document.

Example #1 A sample SCA component

`<?php
include "SCA/SCA.php";
/**
* Calculate a stock price for a given ticker symbol in a given currency.
*
* @service
* @binding.soap
*/
class ConvertedStockQuote {
/**
* The currency exchange rate service to use.
*
* @reference
* @binding.php ../ExchangeRate/ExchangeRate.php
*/
public $exchange_rate;
/**
* The stock quote service to use.
*
* @reference
* @binding.soap ../StockQuote/StockQuote.wsdl
*/
public $stock_quote;
/**
* Get a stock quote for a given ticker symbol in a given currency.
*
* @param string $ticker The ticker symbol.
* @param string $currency What currency to convert the value to.
* @return float The stock value is the target currency.
*/
function getQuote($ticker, $currency)
{
$quote = $this->stock_quote->getQuote($ticker);
$rate = $this->exchange_rate->getRate($currency);
return $rate * $quote;
}
}
?>`

In this example, we see that an SCA component is implemented by a script containing a PHP class and includes SCA.php. The class contains a mixture of business logic and references to other components or services. In the illustrated getQuote() method there is only business logic, but it relies on the instance variables $stock_quote and $exchange_rate having been initialized. These refer to two other components and will be initialized by the SCA runtime with proxies for these two services, whenever this component executes. The annotations for these two services show one to be a local component, which will be called within the same PHP runtime, and one to be a remote component which will be called via a SOAP request. This component also exposes the getQuote() method both locally and as a web service, so it in turn can be called either locally or remotely.