<commit_before>This chapter gives an overview of the overall architecture, terminology and constraints of 
Doctrine 2. It is recommended to read this chapter carefully.

++ Entities

An entity is a lightweight persistent domain object. An entity can be any regular 
php class that obeys to the following restrictions:

* An entity class must not be final or contain final methods.
* An entity class must not implement `__clone` or [do so safely](http://www.doctrine-project.org/documentation/cookbook/2_0/en/implementing-wakeup-or-clone).
* An entity class must not implement `__wakeup` or [do so safely](http://www.doctrine-project.org/documentation/cookbook/2_0/en/implementing-wakeup-or-clone).<commit_msg>[DDC-540] Doc improvement<commit_after>This chapter gives an overview of the overall architecture, terminology and constraints of 
Doctrine 2. It is recommended to read this chapter carefully.

++ Entities

An entity is a lightweight, persistent domain object. An entity can be any regular
PHP class observing the following restrictions:

* An entity class must not be final or contain final methods.
* An entity class must not implement `__clone` or [do so safely](http://www.doctrine-project.org/documentation/cookbook/2_0/en/implementing-wakeup-or-clone).
* An entity class must not implement `__wakeup` or [do so safely](http://www.doctrine-project.org/documentation/cookbook/2_0/en/implementing-wakeup-or-clone).
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