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| Direct manipulation - giving
a testable definition |
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| By Fred
Voorhorst (Zürich, 2000). |
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| Direct
manipulation is an ill-defined concept. It belongs
to the category of quality, intuitiveness, ease
of use and so forth. The typical 'every body knows
what it is when they see it' type of criteria. Because
it is ill defined every body feels competent to
formulate an opinion about it, and those who actually
are competent have no real measuring stick to help
guide development. |
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| On this
page I will present some examples showing how concepts
like direct manipulation and ease of use have been
driven more from a technical point of view and less
from a user's. At the end I propose a measurable
definition for ease of use and direct manipulation. |
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| Qualification
of the user interface is driven by hardware development.
At the time of a keyboard based systems were common,
the mouse-based pointer was considered 'direct manipulation'.
The pen swiftly followed this, when pen based systems
became fashionable. At the moment the virtual reality
systems are topic for research and are the modern
synonyms for ease of use and direct manipulation. |
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| Although
technology improved, the interface did not. The
interface seems to be designed to fit the technology
rather than the task or user. For example, Virtual
reality systems, with the ability to react to any
possible user action, still ask the user to 'push
a button'. Research recently caught up to the fact
that humans actually have two hands, and hopefully
soon will find out these hands is skilled in detailed
manipulation. |
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| To improve
usability and direct manipulation you need to measure
that what hinders these: control over the user interface.
The more time and effort the user has to invest
in controlling the interface the less time and effort
the user can invest in completing the task. |
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| I therefore
propose to use 'time spent in controlling the interface'
as measure for usability. Usability (for a specific
user) is optimal when the task is completed without
ever having to find a button, search for a function
or even having to look at how the mouse is oriented. |
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| Consequence
of this definition is that on the one side usability
becomes measurable, and on the other side that it
becomes decoupled from the hardware implementation;
instead it is coupled to the relation between task
at hand, the user's skill and the hardware. A keyboard
becomes perfectly usable to a professional typist
having to type out the minutes on a Dictaphone.
A mouse does not. |
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