Yousef Nabulsi

Why database abstraction layer ?

A database abstraction layer is a database-independent interface, it is a layer of abstraction over the actual database access methods and allows developers to deal with different databases without changing their code on a per-database basis.

By placing a layer of abstraction between the database and the developer,  the database abstraction layer insulates the programmer from database implementation details.  If you initially write a script to talk directly to Oracle for example and later need to have it work with another database server, you will have to rewrite all the database-specific parts but If you use a database-independent API, then all you need is just to change some littel settings, Pear provide us DB data object that give us good features to accomplish this technque.
  
Now to the Examples

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Introduction

Regular expressions is a way to describing a pattern in piece of text, PHP supports two styles of regular expressions syntax : POSIX and Perl, The Posix style of regular expression is compiled ito PHP by default , but you can use the Perl style by compiling in Perl-compatable regular expression (PCRE) libraray.

 If you used the php matching functions you will note that all pattern matching you have done used String functions, and you have been limited to exact matches, So if you want to do more complex pattern matching you should use the regular expression, it is difficult at first but it is extremely usefull.

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The character encoding is a code that pairs a sequence of characters from a given character set with some thing else to represent it in a form which you can store and transmit it in telecommunication networks, the given characters form before encoded is called character set.
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