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Total Capacity

Design choices affect the capacity of an interface to store pieces of information to a large degree. Such choices limit capacity due to limitations on systems resources (screen space, color, etc.) and human capabilities (short and long term memory, recall, attention, etc.).

Total capacity can be determined using the presentation hierarchy model by successive multiplications of each node capacity along a branch and accumulation of branch capacities at the composite nodes. The unit of the capacity measure can be the count of any of the node instances in the presentation hierarchy. To make comparisons between different interfaces however, one must choose a node which exists in all of the interfaces. For example, the number of web pages can be used to compare the capacities of the WebBook and the Web Forager, the vtwm and the Elastic Windows interfaces.

Using the presentation hierarchy, the total capacity of the WebBook and the Web Forager interface yields tex2html_wrap_inline2318 , i.e. the maximum number of pages in a book times the maximum number of books that can be placed on the shelf, the desk and in the air. For the vtwm interface, the total capacity is tex2html_wrap_inline2320 i.e. the number of pages in a window multiplied by the number of windows that can fit on a desktop times the number of desktops available in an overview. The total capacity of the Elastic Windows interface is tex2html_wrap_inline2322 due to self containment of the window node in the presentation hierarchy. However, this does not tell that its capacity is unlimited. It only states that it is not limited due to the interface design.

Eser Kandogan
Sun Sep 13 18:34:46 EDT 1998

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