p2的相关概念

1.The role of P2
p2的核心构架是agent[代理]，这个agent是抽象的概念，它不是真正的代理对象，它
真实是一个逻辑实体，它用来说明：metadata元数据管理profiles，通过管理
下载aritfacts从仓库repositories中,使用engine来操作profiles.
      artifacts被安装或更新，它大多是一些bundles
      metadata说明：依赖的信息，它从产品配置文件或manifests中抽取得到
      profiles:represent runnable configurations of software,recorded intalled artifact.
     
2.p2 Architecture
      the directors and engine can be remote
     
      All metadata is captured in {installable unit}IUs
     
      IU has an ID and a version,the combination of which must be globally unique.
     
     
      agent
        Director      ->[]Metadata
        TouchPoints   ->[]Runtines  ->[]Eclipse,other,os
        Engine        ->[]app.part,profiles
        Repositories  ->[]Artifact
       
        director is the brains{大脑}of the p2 operation.
                : the metadata available in the known repositories
                  the profile being managed
                  a set of install,uninstall,update operations
       
        Engine : to execute a given set of install,unstall,and update operation.
       
        when a bundle is installed into an Equinox system,its start level
       and auto-start state need to configured,This is done by the Equinox
       touchpoint.
 
  3.Using the p2 Api
    p2暴露一些集合，关于provisional Api
    你可以完全自已的安装向导，以及整个工作流程。
    IProfileRegistry
    IInstallableUnit
    IPlanner
    IEngine
    IMetadataRepositoryManager
    IArtifactRepositoryManager
   
   4.publishing Metadata
     三种创建repositories方法：
      导出向导，PDE Build,使用publisher