Introduction
WarningThis 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.
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