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PHP is an intuitive, server side scripting language. Like any other scripting langauge language it allows develpers developers to build logic into the creation of web page content and handle data returned from a web browser. PHP also contains a number of extensions that make it easy to interact with databases, extracting data to be displayed on a web page and storing information entered by a web site visitor back into the database.

When a user visits a web site or clicks on a link on a page the browser sends a request to the web server hosting the site asking for a copy of the web page. The web servber server receives the request, finds the corresponding web page file on the file system and sends it back, over the internet, to the user's browser.

Now let's consider what kind of web page content a web browser understands. These days a web page is likely to consist of HTML, XHTML and JavaScript. The web browser contains code that tells it what to do with these types of content. For example, it understands the structure HTML in terms of rendering the page, and it has a JavaScript interpreter built in that knows how to execute the instructions in a JavaScript script. A web browser, however, knows absolutely nothing about any PHP script that may be embeeded embedded in an HTML document. If a browser was serverd served a web page containing PHP it would not know how to interpret that code.

where Once loaded into the browser, it is rendered just like any other web page. The fact that the web page originally contained PHP is completely transparent to the web browser.

The above example is certainly an oversimplification of the pwer power of PHP. Some may question why one would use PHP to output some static text that could have been achieved more easily using an HTML tag. The fact is, however, HTML only makes sense if you know before hand beforehand exactly what needs to be displayed in the web page. Imagine instead, that you are developing an online banking application. One of the pages you need to display must contain the customer's bank account number combined with the current balance. Obviously this information is going to be different for each customer. In this scenario you would develop an HTML page that essentially serves as a template for the page, and then embed PHP into the page to extract the account and balance information from a database. Once processed by the PHP module integrated into the web server, this customer specific content will then appear in the HTML page in place of the PHP script when the page is loaded into the browser.

When talking about JavaScript it is important to understand that it is, by design, a client side scripting language. By this we mean that the script gets executed inside the user's browser and not on the web server on which the web page originated. Whilst this is fine for many situations it is often the case that by the time a script reaches the browser it is then either too late, or inefficient, to do what is needed. A prime example of this involves displaying a web page which contains some data from a database table. Since the database resides on a server (either the same physical server which runs the web server or on the same network as the web server connected by a high speed fibre fiber network connection) it makes sense for any script that needs to extract data from the database to be executed on the server, rather than waiting until it reaches the browser. It is for this kind of task that PHP is perfectly suited. It is also fast and efficient (because the script is executed on the server it gets to take advantage of mutlimulti-processing, large scale memory and other such enterprise level hardware features.

In addition to the advantages of being a server side scripting language PHP is easy to learn and use. The fact that PHP works seemlessly seamlessly with HTML makes it accessible to a broad commumity community of web designers.