With the Eclipse provisioning system p2 what is a feature and a plugin

I'm trying to get my head around some of the concepts and I understand what a profile is and what an installable unit (IU) is but I'm struggling wit开发者_如何学JAVAh plugins and features. Does anyone have any insight. How do they relate to profiles and IUs?

Thanks in advance, Chris.

From eclipse wiki

Installable Unit:

As the name implies, Installable Units (IUs for short) describe things that can be installed, updated or uninstalled. They do not contain the actual artifacts but rather essential information about such artifacts (e.g., names, ids, version numbers, dependencies, etc) and are not aware about what they deliver. They describe things. They are NOT the things. So for example an IU for a bundle is NOT the bundle. The bundle is an "artifact". The metadata allows dependencies to be structured as graphs without forcing containment relationships between nodes. Here is detailed presentation of what an installable unit is made of.

In this context features and plug-ins are artifacts.

A plug-in in Eclipse is an OSGi bundle which may contain UI contributions and make use of Eclipse extension points. A feature is a collection of plug-ins, fragments and features.