WIMOVAC Parameter Database

A wimovac model module can be run with the default settings by simply clicking the start button on the appropriate dialog (Figure 7vi). Alternatively the properties of the model may be explored by varying model parameters. This is done in wimovac by either editing input values, multiple choice selectors and action buttons on the model dialog form itself (Figure 7, Figure 7), or by modifying the model parameter database (Figure 9, Figure 10). Because wimovac includes over 200 potential input parameters, it is most practical to have two levels of parameter entry. The most commonly modified parameters and initial conditions for a sub-model are accessible on the model dialog itself, these parameters are commonly the driving variables of the model.

These and all other parameters can also be accessed by entering the model parameter database. Changes made on the form are only active until the form is closed, permanent changes must be made in the model parameter database, using the File-exit and save changes option, on completion. In situations where a parameter occurs in both the model database and on a model dialog form the value outlined on the form takes precedence when the model is run.

Traditionally model parameter files have been manipulated as complex ASCII files and required a separate ASCII file text editor. There are a number of problems with this approach however. These include difficulties with starting a separate text editor program within the modelling environment, and the discontinuity of user interface that this represents, and the complex formatting and abbreviations generally used in such files. To avoid these problems and to meet the specifications on ease of use, wimovac, employs a parameter database editor in a spreadsheet format which is consistent with the structure and user interface of the rest of wimovac. This spreadsheet like mode of operation will be familiar to anyone who has used a modern spreadsheet package such as Lotus 123 for Windows or Microsoft Excel. The wimovac parameter database editor is called in a seamless fashion from the model dialog menu (Figure 8ii) and appears as an integral part of the modelling environment itself. The parameter database editor has facilities to cut, copy and paste information from other applications using the Windows clipboard and to search for text entries and values within the parameter database. It is also possible to printout either selected areas or the whole of the database to any printer supported by Windows. A typical search of the database entries takes less than a second on a 25MHz 80486 machine.

To help users find model parameters more easily the model parameter database is hierarchically organised in a similar manner to the model module launcher. When the model parameter database option is selected from the menu line (Figure 8ii) the outliner dialog shown in Figure 9 is opened as a child window. From this dialog the user can choose to work with a either the whole parameter database or more selectively with one of the sub-module parameter sheets. The hierarchical organisation of parameter sheets used by the database once again reinforces the scaling process of the model and allows the user to quickly identify which parameters have a direct effect on a given sub model. Once a user has selected which part of the database they wish to work with the necessary parameters are automatically retrieved from the database and displayed in the form of a parameter database input form.

Figure 9. Model parameter database hierarchical outline. i) Access to all model parameters in a single table. ii) Double clicking on a closed folder expands the selection hierarchically to show the sub parameter properties of the selected category. Open folder indicates that the database category is expanded and sub parameter properties should be visible. (iv) Double clicking on the document icon lines shows requested portion of the model parameter database. v) Displays the help file. vi) Alternative to double clicking to show selected parameter section. vii) Close hierarchical view of parameter database. Note that this dialog has a grey background to make it easy to distinguish from the model module launcher.

The complexity of mechanistically rich models strongly emphasises the need for "self documenting" models and parameter datasheets. A good model should be accompanied by documentation that describes as a minimum, i). Underlying model assumptions ii). Sources of model theory and details of the algorithms used iii). Sources of model parameters on an individual parameter basis. The underlying assumptions of the vegetation model in wimovac are dealt with in the help system. However some of the information about sources of model theory, details of algorithms used and sources of model parameters on an individual basis are best located as close to the model parameters as possible. Consequently the parameter database input form consists of a dialog with four columns. The first column contains a plain English description of the parameter, units of the parameter and where applicable the range of acceptable values and a suitable default value (Figure 10iv). The second column contains the parameter value (Figure 10v) and the third the literature citation from which the parameter was obtained (Figure 10vi). The fourth column contains a textual reference to the parameter, which is used by wimovac to search for the parameter within the database (Figure 10vii). The user may modify any of these settings and include their own notes and experimental findings.

Wimovac saves any changes made to the parameter database to two separate disk files. The first of these is a plain ASCII, tab delimited, file for use with applications outside of wimovac. The second file is a specialised ASCII file compatible with the string handling facilities built into Windows and is the file used by wimovac model dialogs. The Windows string handling functions are highly optimised and make it possible to search for hundreds of model parameters within the database in just a few seconds. The wimovac parameter sheet also allows copies of the parameter database to be saved to disk under any MS-DOS/Windows compatible file name and this makes it possible to set up multiple test scenarios using different parameter datasets and to permanently store these on disk. Saving all the model parameters needed to perform a model run to a single file, in this manner, makes it easier for a researcher to send all the information needed to duplicate a piece of work to other workers for validation and discussion.

Figure 10. Model parameter database dialog. i). Top lines of each parameter section contain the software switches which control model behaviour and allow selection between optional model components. ii) User input box which is automatically validated for datatype. iii) Parameter sheet cursor operated with cursor keys allows entry and modification of text and parameter values. iv) An optional field that contains the parameter description and where aplicable the range of acceptable values which may be entered into the parameter field. v) Compulsary field containing the model parameter value. vi) Optional field containing the literature citation or other related information. vii) Compulsary field containing a unique search description for parameters, used internally by wimovac to find the model parameter in the database.

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Last modified: August 19, 1997