91 
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Figure 3: Example of a widget developed under Tcl/Tk for the editing of the model inputs. 
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created, in which interaction is possible only to a limited extent. 
Tcl/Tk is a scripting tool that allows a user to build, in a simple way, graphical front-ends to any 
kind of application [Ousterhout 1994]. Tcl/Tk is similar to many other scripting tools, and is easy 
to learn. It is available freely as a public domain package. This is an advantage in a collaborative 
project involving various institutes, since all partners can have access to the applications built with 
it. 
A part of the Tcl/Tk interface being developed for the hydrologic model is shown in Figure 3. 
The widget controls the input of the parameters necessary to generate the 3D mesh and initial 
conditions for the model. The script simply accepts the input data and re-writes them in the 
format of the original input file. During this process validity checks can easily be applied, and 
it becomes also easier to produce different versions of a file or to provide the user with default 
configurations. Numerical flags are substituted by checkbuttons. The widget may even change its 
appearance, according to the selected options, leaving to the user only a minimum set of displayed 
parameters, while “hiding” those which are not necessary. Such front-ends to the input phase can 
be developed without modifying the structure of the input files for the model. This allows a very 
fast, though not always optimized, implementation.