DOM

Although DOM support in PHP 4 was also based on the libxml2 library, it was quite buggy, had memory leaks and the API in many cases was not W3C compliant. The DOM extension went through a thorough facelift for PHP 5. Not only was the extension mostly rewritten it is now also W3C complaint. For example, function names now use studlyCaps as described by the W3C standard making it easier for you to read general W3C documentation and implementing what you learnt, right away in PHP. In addition, the DOM extension now supports three kinds of schemas for XML validation, DTD, XML Schema and RelaxNG.

As a result of these changes PHP 4 code using DOM will not always run in PHP 5. However, in most cases adjusting the function names to the new standard will probably do the trick.

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XSLT

In PHP 4, there were two extensions that supported XSL Transformations. The first was using the Sablotron extension and the second was using the XSLT support in the DOM extension. In PHP 5, a new XSL extension was written and, as mentioned, is based on the libxml2 extension. As in PHP 5, the XSL Transformation does not take the XSLT stylesheet as a parameter but depends on the DOM extension to load it, the stylesheet can be cached in memory and may be applied to many documents saving execution time

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SimpleXML

Probably when looking back in a year or two it will be clear that SimpleXML has revolutionized the way PHP developers work with XML files. SimpleXML could really be called "XML for Dummies". Instead of having to deal with DOM or even worse SAX, SimpleXML represents your XML file as a native PHP object. You can read, write or iterate over your XML file with ease accessing elements and attributes.

Consider the following XML file:

<clients>
<client>
<name>John Doe</name>
<account_number>87234838</account_number>
</client>
<client>
<name>Janet Smith</name>
<account_number>72384329</account_number>
</client>
</clients>

The following piece of code prints each client's name and account number:
$clients = simplexml_load_file('clients.xml');
foreach ($clients->client as $client) {
print "$client->name has account number $client->account_number ";
}

It's obvious how simple SimpleXML really is.

And in case there is something advanced you need to do to your SimpleXML object which isn't supported in this lightweight extension, you can convert it to a DOM tree by calling dom_import_simplexml(), manipulate it in DOM and covert it back to SimpleXML using simplexml_import_dom(). Thanks to both extensions using the same underlying XML library switching between these two has been made a reality.

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SOAP

Official native SOAP support in PHP 4 was lacking. The most commonly used SOAP implementation was PEAR's but as it was implemented entirely in PHP it could not perform as well as a built-in C extension. Other available C extensions never reached stability and wide adoption and, therefore, were not included in the main PHP 5 distribution.

SOAP support in PHP 5 was completely rewritten as a C extension and, although it was only completed at a very late stage in the beta process, it was incooperated into the default distribution due to its thorough implementation of most of the SOAP standard.

The following calls SomeFunction() defined in a WSDL file:

$client = new SoapClient("some.wsdl");
$client->SomeFunction($a, $b, $c);

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New MySQLi (MySQL Improved) extension

For PHP 5, MySQL AB has written a new MySQL extension that allows you to take full advantage of the new functionality in MySQL 4.1 and later. As opposed to the old MySQL extension, the new one gives you both a functional and an object oriented interface so that you can choose what you prefer. New features supported by this extension include prepared statements and variable binding, SSL and compressed connections, transaction control, replication support and more...

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SQLite extension

Support for SQLite was first introduced in the PHP 4.3.x series. It is an embedded SQL library which does not require an SQL server and is very suitable for applications which don't require the scalability of SQL servers or if you're deploying at an ISP who doesn't give you access to an SQL server. Contrary to what its name implies SQLite is very feature rich and supports transactions, sub-selects, views and large DB files. It is mentioned here as a PHP 5 feature because it was introduced so late in the PHP 4 series and as it takes advantage of PHP 5 by providing an object oriented interface and supporting iterators.

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Tidy extension

PHP 5 includes support for the useful Tidy library. It allows PHP developers to parse, diagnose, clean and repair HTML documents. The Tidy extension supports both a functional and an object oriented interface, and it's API uses the PHP 5 exception mechanism.

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Perl extension

Although not bundled in the default PHP 5 package, the Perl extension allows you to call Perl scripts, use Perl objects and use other Perl functionality natively from within PHP. This new extension sits within the PECL (PHP Extension Community Library) repository.

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New memory manager

The Zend Engine features a new memory manager. The two main advantages are better support for multi-threaded environments (allocations don't need to do any mutual exclusion locks) and after each request freeing the allocated memory blocks is much more efficient. As this is an underlying infra-structure change you will not notice it directly as the end-user.

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Dropped support for Windows 95

Running PHP on the Windows 95 platform is not supported anymore due to it not supporting functionality which PHP uses. As Microsoft has officially stopped supporting it over a year ago the PHP development community decided that this is a wise decision.

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A Completely Rewritten MySQL Extension

Many developers power their web sites with MySQL.

Also, the latest versions of MySQL, 4.1 and 5.0, introduce many new features, some of which require significant changes to the extension. As a result, PHP 5 comes with a completely new and improved MySQL extension. Dubbed MySQLi, for MySQL Improved. It offers:

* Prepared statements
* Bound input and output parameters
* SSL connections
* Multi-query functions

MySQLi even takes advantage of PHP 5's new object-oriented support to provide an OO interface to MySQL. On top of that, the latest versions of MySQL now enable subselects, transactions, and replication.

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Design Patterns

As previously discussed, the ability to use design patterns in large (and often also small) PHP software projects is extremely important. It was possible to take advantage of such patterns in PHP 4, but—lacking important language features such as static properties and methods, PPP access modifiers, and interfaces—it was often hard to enforce all of the semantics of these patterns.

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Singleton Pattern

An often-used and excellent example is the Singleton pattern. Although it is one of the simpler patterns, in order to implement it in its entirety, static properties and methods and PPP access modifiers are a necessity.

For example:

<?php

class MySingleton {
static private $instance = NULL;

private function __construct() {
}

private function __clone() {
}

static public function Instance() {
if (self::$instance == NULL) {
self::$instance = new MySingleton();
}
return self::$instance;
}
// ... Additional code for the MySingleton class.
}

This implementation takes advantage of the new PHP 5 features, which results in a cleaner and less error-prone Singleton implementation. For example, the ability to declare the constructor and clone methods as private prevents developers from mistakenly instantiating an additional copy of the MySingleton class, as only the class itself may access these methods. The support for static properties is used in order to have a globally accessible property (self::$instance) that references the single instance of the class. Declaring the property private makes sure that only the class itself may fiddle with this property.

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Immutable Object Pattern

Another slightly less common design pattern is the Immutable Object pattern. This pattern is usually used in applications where a large amount of references to a relatively small group of values exists. It allows the application's code to share objects by making the objects immutable (forbidding their state to change), and forcing code that wants to do so to create a new instance of the class.

The following example shows how you can create a class that represents a SQL query. The assembled query statement itself might be used in many places in your application. Code that wishes to change the value of the query may do so using the changeStmt() method, which returns a handle to a new object that represents the specified query string.

<?php

final class ImmutableQueryStatement {
private $stmt;

public function __construct($stmt) {
$this->stmt = $stmt;
}

public function getStmt() {
return $this->stmt;
}

public function changeStmt($stmt) {
return new ImmutableQueryStatement($stmt);
}
}

This example takes advantage of a few new PHP 5 language features. To begin with, it uses the final keyword so that the class may not be "subclassed." This approach prevents developers from subclassing and implementing a version that may be mutable. In addition, changeStmt() takes advantage of the new object handles and returns the newly created object by-value (in PHP 4, a new object instance would have to be returned by reference, complicating the implementation). Last but not least, similar to the previous example, access modifiers are used to specify the access contract this class should adhere to.

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PHP5 with Oracle

General Released in July 2004, PHP 5 has only been around for a short time. Despite that, there are already quite a few interesting things happening in PHP development. There has been a lot of work on improving the performance of the scripting engine and, most importantly for the Oracle readers, there are many new database-related initiatives. Use of Oracle is strong in the PHP community, and a large amount of Zend customers are Oracle users. Their use of Oracle varies as it does with other databases but is usually a very conscious choice, which has to do with Oracle's proven track record, advanced features, and often an already existing investment in Oracle infrastructure.

Scripting Engine Performance When developing PHP 5, Zend and the community focused more on functionality than on performance. Therefore, except for a few exceptions, performance of the scripting engine was not improved between PHP 4 and 5.

In most PHP applications, the raw execution performance of PHP is not the main bottleneck. The most common bottlenecks are related to I/O and are usually database-related. That said, we still believe that improving the performance of the scripting engine itself will definitely benefit the PHP user. For this reason, we decided to invest significant resources to improve performance for PHP 5.1.x.

Since the release of PHP 5, we have invested a lot of resources in tuning the scripting engine. Many ideas were taken from a performance patch that Thies Arntzen and Sterling Hughes published about a year ago. Other ideas came from inside Zend and the PHP developer's community. The end result is an engine that is commonly more than twice as fast as PHP 4.0 and PHP 5.0 for synthetic benchmarks (benchmarks that don't include I/O and real-world code).

The improvement is quite impressive, and when PHP 5.1.0 is released all of the PHP users will enjoy it without having to make any changes to their source code. I believe that PHP 5.1.0 will be released early in the first quarter of 2005, but one can never tell with an open source project.

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SQL Relay

SQL Relay (is a very interesting third-party project. It is a project that implements a proxy broker for SQL connections (including Oracle), allowing for connection pooling of database connections using PHP.

The project provides its own version of a PHP database extension (you will be required to change your PHP database code). This extension talks to the SQL Relay broker that relays queries and result sets to and from the database.

Some of SQL Relay's advantages:

* Using connection pooling, you can limit the amount of open connections to the database.
* In case PHP persistent connections can't be used in your environment, this solution solves the problem of long connect times when initiating an Oracle database connection.
* The project supports other programming languages too. If you have a hybrid environment, you can take advantage of the same SQL Relay daemons that are being used from PHP. In addition to PHP, language support includes C, Java, Perl, and quite a few more.
* Getting up and running with SQL Relay, although not trivial, is quite simple. I'd also like to note that the SQL Relay author was very responsive to my questions.

Some of SQL Relay's disadvantages:

* You have to use a different API than the PHP Oracle extension.
* Result sets are copied twice: first to the SQL Relay broker and then to PHP.
* You don't have as rich an API as you do when using PHP's native oci8 extension.

I think that if your project does require Oracle database connection pooling, it is a good idea for you to check out SQL Relay. It might not be perfect, but it might still take a while until a better solution comes along, and this one does seem to work.

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PDO

The PHP community has been working on a new database abstraction layer in addition to the existing oci8 PHP extension that has a native interface to the Oracle Database. As Oracle Technology Network already has an in-depth article covering PHP Data Objects (PDO), by Wez Furlong, suffice to say that PDO is something to watch. PHP has been waiting for quite some time for good native database abstraction. I believe that PDO may very well be the solution we have all been waiting for. The designers of PDO are some of the lead developers of the PHP community, and I like their approach with PDO. The following is a list of their design goals, as written in the PDO README file:

1. Be lightweight.
2. Provide a common API for common database operations.
3. Result in high performance.
4. Keep the majority of PHP-specific code in the PDO core (such as persistent resource management); drivers should only have to worry about getting the data and not about PHP internals.

On one hand it gives a common API for working with databases. But it also allows each driver to add its own additional functionality, so that PDO not only supports the least common denominator of the database APIs but will actually give you the opportunity to use all the features your database has to offer. And we all know Oracle has lots of them.

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Propel

Propel is an object persistence and query framework. It implements object/relational mapping (ORM) and is based on the Apache Torque project, which does the same for Java. Unlike PDO, Propel is a very high-level database abstraction layer, redefining how you query, create, and manipulate persistent objects. Propel, as expected from an OO/RDBMS mapping system, also deals with database schema creation.

There are many advantages to a system like this. For starters, developers can concentrate most of their time on writing business logic and have to deal less with the intricacies of the database—whether it is schema management or writing fancy SQL statements. Database manipulation is very natural, as developers just deal with regular objects and the persistence layer deals with the low-level details of updating the right fields and rows in the database.

The disadvantage is that you do lose some control. The automatic mapping of the OO model to the relational database is not always straightforward. Not only does it make it hard to write fancy, powerful, hand-crafted queries, but you're also not supposed to do so—you break the abstraction, and a tiny update of the mapping might break the application. Therefore, using such a system means you have to play by the rules of the tool. In most cases, this price is acceptable, as increased productivity helps shorten development times and improves code quality. However, there are certain instances where you might absolutely require this control.

Propel is a very interesting project and can come in handy. In addition, it is built on top of a database abstraction layer called Creole. Unlike PDO, this abstraction layer tries to mimic JDBC as much as possible and might be easier to use if you are converting existing Java code to PHP. That said, if PDO becomes mainstream and is distributed as part of standard PHP, it might be best to stick with that.

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