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MS Project: Data Types - Task, Resource, Assignment

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Project stores and uses data as one of three individual types – Task, Resource and Assignment.  Assignment data bridges task and resource data by matching resources to the task. Each data type has several extra fields associated with it. There are extra text fields, cost fields, etc., and they are all independent, that is, Task Text1 is not the same as Resource Text1 nor is it the same as Assignment Text1. When using Project Professional with Project Server several more enterprise level extra fields are available.
 
When in a task view (e.g. Gantt Chart), only task data can be shown and in a resource view (e.g. Resource Sheet), only resource data can be shown. The Usage views (Task or Resource) are special combined views that display either task and assignment data or resource and assignment data. When extra fields are displayed in a Usage view they must be properly interpreted. If Text1 is shown in the Task Usage view, task rows will display Task Text1 while assignment rows will display Assignment Text1 - and they are completely different and independent.
 
Task and Resource extra fields are customizable by the user. Custom attributes can consist of:

  • Renaming a field so it is more easily recognized. This is called a “friendly” name.
  • Defining a set of values for the field that the user can select from a value list.
  • Calculating a value for the field using a formula. The calculated value can be a number, date, boolean, or text depending on the field type.

In addition, graphical indicators can also be displayed by setting some simple rules. Extra Assignment fields cannot be renamed or contain formulae or value lists but they can be customized with user data. However, in either Usage view Task or Resource value list data can be rolled down to Assignment rows.
 
Project versions up through 2003 have only one set of assignment extra fields. Project 2007 introduced two types of assignment extra fields - those visible in the Task Usage view (Task Assignment fields) and those visible in the Resource Usage view (Resource Assignment fields), and they are completely different.
 
When customizing an extra field with a formula, the formula is only applicable to views of that data type. For example, if a formula is created for Cost1 in the Resource Usage view, it is a Resource Cost1 formula and will ONLY apply to resource data, not to the assignment data, which may also be shown in the view.
 
For versions of Project earlier than 2003 grouping works similar to formulae, that is grouping only applies to task or resource data. Project 2003 added the functionality to allow grouping on task/resource OR assignment data when in a Usage view but the user does need to specify the proper Field Type when selecting the assignment option.
 
Filters are a little more flexible. If a filter is applied to a Usage view, it will filter on both the resource/task data and the assignment data. For example if a simple filter for Flag1 is applied to the Resource Usage view, the result will include all resource rows with [resource] Flag1 AND all assignment rows with [assignment] Flag1.
See also wiki [ MS Project: Extra fields in views http://social.technet.microsoft.com/wiki/contents/articles/32051.ms-project-extra-fields-in-views.aspx

Source reference: This is a revision of MVP FAQ 51 - Data Types: Task, Resource, Assignment: http://project.mvps.org/faqs.htm#Data_Types:_Task,_Resource_and_Assignment