Intranet Design Magazine: Free Software Profile: PHP

By Christophe Lauer, TechMetrix Research

PHP at a glance

General Overview

PHP is an HTML-embedded scripting language. Like Microsoft’s ASP
technology, it is designed to be processed on the server side and
produce dynamic Web pages.

PHP3 is the third version of the interpreter initially developed
by Rasmus Lerdorf. It was originally destined to bring dynamic
scripting functionality to personal HTML Web pages, which explains
why it was christened Personal Home Page. For the second version of
PHP, its engine was rewritten so that HTML form management
functionality could be added, and its name became PHP/Form
Interpreter (PHP/FI) to reflect this change. The arrival of PHP3
coincided with the rise of the Internet wave, a time when many
personal and professional users were in need of dynamic behavior on
their Web sites: online catalogs and e-commerce applications with
shopping cart management. PHP now officially stands for PHP:
Hypertext Preprocessor.

PHP4 has finally obtained the ‘Release’ tag and can be
downloaded at http://www.php.net./version4. Many high-traffic sites
have already been using PHP4 for several months and no major
problems have been reported. The interpreting engine has been
completely rewritten in PHP4. In terms of internal architecture,
this means that the interpreter is clearly separated from the rest
of PHP (even if this is totally transparent to users or
developers). In light of this, PHP’s developers came up with a
generic engine called Zend (http://www.zend.com/), whose name is a contraction of its
author’s names: Zeev Suraski and
Andi Gutmans.

Architecture and Functionality

PHP3 and PHP4 are open software programs. Indeed, they propose
an API that can be used to add functions to the languages. It is in
this manner that numerous contributors progressively built upon the
language’s core functions and instructions by adding functions that
make it possible to exploit all of the language’s protocols and
standards. The following elements can be cited as examples: an XML
parser, manipulation of WDDX data, access to LDAP directories, and
support for IMAP, POP and NNTP protocols. As such, PHP natively
provides access to all existing. and future. intranet standards,
and this is in a large part due to the community of developers
involved in PHP’s development. Moreover, PHP interfaces with a
large number of proprietary and free DBMSs (MySQL, PostgrSQL,
Oracle, Sybase, Informix, IBM DB2 and so on). Unlike Perl which
offers an abstraction layer via DBI and DBDs, access to the various
DBMSs depends on DBMS-specific functions. PHP does not offer
database connection pooling.

PHP is multi-platform when it comes to operating systems and
HTTP servers. Thus, PHP can run on all free and proprietary Unix
systems, and on all HTTP servers supporting at least the CGI
interface.

Nonetheless, PHP’s favorite platform remains the one made up of
the Unix/Apache couple. PHP3 can be used in CGI mode on most HTTP
servers, but it offers the most features and much better
performances when it is used as a loadable Apache module (like
mod_perl). With PHP4 one now has the possibility to use PHP as an
ISAPI filter with Microsoft’s HTTP server.

PHP4’s architecture is more open and scalable than that of PHP3,
characteristics that spawned the ISAPI interface. Among its new
functionalities, one finds session management and context variable
manipulation primitives. In its latest version, PHP4 provides
openness to the world of Java, thus enabling servlet execution and
direct instantiation and manipulation of Java classes as if they
were simple PHP classes. This “gateway” to Java has been tested
using the JVMs of Sun, BlackDown and Kaffe on Linux and Windows NT
systems only.

In terms of performance, PHP4 improves on its predecessor by at
least 15%. In order to obtain even better performances, one must
use PHP4 extensions. One of the three extensions, the optimizer,
can currently be downloaded at no charge. It is important to point
out that this optimizer is situated at the level of the
interpreter’s Zend engine. Therefore, this optimizer is not
available under a free license, but under the same license as Zend,
the QPL. One of the other announced extensions is the execution
cache, which follows the same principle as the mod_perl Registry by
enabling the storage of scripts that have been pretokenized,
preanalyzed and preprocessed. The third extension will be a
compiler for all PHP scripts. However, the compilers will probably
come from third-party vendors and may be available under a free
license.

PHP’s open API makes it possible to extend the language by
adding processing functions that are coded in C and used from PHP.
These functions aim to improve performance, and do so in a
transparent manner. In practice, this possibility is never used.
The arrival of optimizers and other third-party compilers should
provide a more elegant solution to performance problems than a
combination of C and PHP.

Beyond the language itself, one of PHP’s current strengths is
that is offers a set of “ready-to-use” building blocks that were
developed by PHP users and made available under free licenses.
Among these essential building blocks one finds database
administration interfaces such as phpMyAdmin and postgresAdmin;
interactive forums such as Phorum, NeoBoard and W-Agora; HTML mail
server access interfaces such as IMP, FocalMail; management of
shared calendars and agendas such as TimeSheet and Keystone;
indexing and search engines such as UdmSearch; HTML page templates
such as FastTemplate; e-commerce business solutions such as eShop
and FishCartSQL; and helpdesk management such as Ministry of Truth.
Distribution

• PHP is principally available as source code for Unix and
  similar systems, and Windows platforms. Nonetheless, the binary
  units that are precompiled for Windows can be downloaded directly
  from the official Web site.
• PHP has become a part of all Linux distributions; it can be
  found as RPM or DEB packages, or in the software packages ported to
  FreeBSD.
• No official support, but there is a mailing list.
• GNU GPL for PHP3, PHP License for PHP4 (see details), but it
  is important to note that the Zend engine is available under a QPL
  license, which is the license for Troll Technologies’ Qt
  library.

Reprinted from www.techmetrix.com

TechMetrix Research is a technically focused analyst firm
focused on e-business application development needs. Based in
Boston, Mass., the firm publishes comparison reports and product
reviews designed to aid enterprises with decision making and to
keep pace with the fast-moving e-business market.

TechMetrix is a U.S.-based subsidiary of SQLI, a European web
agency that offers on-site development services to international
organizations. SQLI specializes in e-business project
development.