php4 to php5 migration

We got project, its migration site开发者_如何学C from php4 to php5,

What are the thing first i should do,

In which parts i should concentrate,

Is there any procedure ,

Give top high 15 point for php4 to php5 migration,

Guess client using the Informix , ut not sure, may be Mysql also,

To be honest, what you probably need to do is simply study the Migrating from PHP 4 to PHP 5 FAQ and the more detailed Migrating from PHP 4 to PHP 5.0.x section of the PHP manual - as this will tell you pretty much all you need to know.