doctrine2/manual/docs/Coding standards - Naming Conventions - Constants.php

Following rules must apply to all constants used within Doctrine framework:

<ul><li \> Constants may contain both alphanumeric characters and the underscore.</ul>

<ul><li \> Constants must always have all letters capitalized.</ul>

<ul><li \> For readablity reasons, words in constant names must be separated by underscore characters. For example, ATTR_EXC_LOGGING is permitted but ATTR_EXCLOGGING is not.
</ul>
<ul><li \> Constants must be defined as class members by using the "const" construct. Defining constants in the global scope with "define" is NOT permitted.
</ul>

<code type="php">
class Doctrine_SomeClass {
    const MY_CONSTANT = 'something';
}
print Doctrine_SomeClass::MY_CONSTANT;
</code>