请教高手关于RIM:Role

JohnDoe

在Role中有一个域positionNumber : LIST<INT>不知道干什么用的，英文解释：
An integer specifying the position of the Entity playing the Role with respect to the Entity that scopes the Role.</p>

<i>Discussion:</i> This attribute is primarily used with respect to containment roles.  For example, some containers have discrete positions in which content may be located. Depending on the geometry of the container, the position may be referenced as a scalar ordinal number, or as a vector of ordinal numbers (coordinates). Coordinates always begin counting at 1.</p>

Some containers may have customary ways of referring to the positions or no way at all. In the absence of any specific regulation for a specific container type, the rule of thumb is that the coordinate that is changed earlier is positioned first. For an automated blood chemistry analyzer with a square shaped tray, this means that the first coordinate is the one in which direction the tray moves at each step and the second coordinate is the one in which the tray moves only every 10 (or so) steps.</p>