2010/12/15 - Apache Excalibur has been retired.  For more
information, please explore the Attic.  Avalon Framework - Guide
- COP in Avalon  Components in Avalon  At the core of the Avalon
framework is the component. We define it as "a passive entity
that performs a specific role". This is important to grasp
because it requires a specific way of thinking.  A passive API
A passive entity must employ a passive API. A passive API is one
that is acted upon, versus one that acts itself. See the
Inversion of Control pattern for an explanation.  A specific
Role  The concept of roles comes from the theater. A play,
musical, or movie will have a certain number of roles that
actors play. Although there never seems to be a shortage of
actors, there are a finite number of roles. I am not going to
make reference to different types of roles at this point, but
simply bring the concept to light. The function or action of a
role is defined by its script.  We are introducing this concept
now because you need to have it in mind