Today I created a abstract layer for accessing a database in PHP. This class includes such operator
as "connect","disconnect","executeQuery",and so forth. My purpose is to provide a uniform interface
of accessing database. So,I created two sub classes of that class. One is to access MysqL database.
Another is to access Postgresql database.

To seek a property sub classes I created a special class to adapt a sub class in according to a argument.That is a factory class,in acutal fact,it is a adaptation.