One of Activity Attributes - effort type

PMBOK 2004 3rd P130中提到活动的属性可以包括该活动的类型，例如 level of effort(LOE), discrete effort(DE) and apportioned effort(AE), 第一次看到这几个概念，从字面不太好理解其含义，在这里找到了一些解释，可以帮助理解:

A Work Package describes the work to be performed by a specific organizational unit, and serves as a vehicle for monitoring and reporting on progress, cost and schedule. All work packages fall into one of three different categories:

• Discrete Tasks which have a specific end result or objective. These normally cover 60 to 75 percent of the total work in a project.
• Apportioned-effort Tasks which can be directly related and apportioned to discrete tasks. Examples include quality control or inspection. These tasks are required in support of the discrete tasks, and hence, their schedule and budget can be related to the discrete tasks.
• Level-of-effort Tasks which have performance standards rather than specific end results. These consist mainly of the overhead accounts, e.g., management, administration, liaison, coordination, etc. These tasks are characterized by relatively level, time-phased budgets and are not time-limited as in the case of the discrete tasks.