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affect the model. All of this may require that the user also understand the directory structure of the <br />model and know how to use an editor of some type in order to edit input files. Additionally, in order <br />to get meaningful results from the output of the model, the user may need to translate the output into <br />a graphical format. <br />The purpose of a GUI is to minimize or eliminate any need for the user to know about the underlying <br />structure of a model's input and output. The GUI consists of some type of menu or icon driven user <br />interface that allows the user to graphically select and edit parameters of interest. The user is then <br />free to concentrate on analytical tasks and will hopefully be able to perform analyses with less effort <br />and can therefore perform a more thorough analysis in a given time. <br />The development of GUIs for complicated applications can result in a GUI that is equally <br />complicated and which may require extensive budget to complete. Because the focus of the CRDSS <br />is to develop products that provide sound engineering results, the resources devoted to GUI <br />development (and the resulting GUI products) must be weighed to ensure that the effort does not <br />deter from the main goals of the project. Guidelines must be set in place so that the future <br />RTi therefore proposes that limits be <br />development of GUIs within the CRDSS are not hindered. <br />placed on GUI development but that a firm foundation for GUI components be built such that <br />future enhancements to applications can build on this foundation <br />. <br />Limits on GUI development are discussed in the individual task memoranda related to GUI <br />components (time series plotting, network display, general map display). The remainder of this <br />discussion concentrates on the details of implementing the foundation for GUIs. Other task <br />memoranda (some to be written in Phase II(a)) discuss very detailed design of GUI components, e.g., <br />the specific design of a diversion structure form. <br />Background on GUI Builders <br />A GUI builder is a product that allows the developer to build a GUI by using a what-you-see-is- <br />what-you-get (WYSIWYG) GUI. For example, the GUI builder allows the user to create menus and <br />buttons by selecting appropriate features from a selection box in the GUI builder. The developer can <br />then size and position the menus and buttons in the GUI application. The product that is being <br />developed is shown as it would appear to the end-user. A GUI builder also typically allows the <br />specification of event callbacks (e.g., when event X happens, call Y routines to perform an action). <br />After initial development with the GUI builder, the GUI code components will be in a form that is <br />suitable for a prototype and can be revised during further sessions with the GUI builder. <br />Depending on which GUI builder is used, the products of a GUI builder may be one or both of the <br />following: <br />source code that can be compiled to create an executable program, <br />? <br />a macro-language version of the code that can be interpreted. <br />? <br />The GUI builder typically creates an executable program by calling a compiler and linking in <br />appropriate graphics libraries. Source code that is generated by a GUI builder conforms to the <br />conventions of the author of the GUI builder software. Quite often, this code is not very <br />understandable to developers because the code makes reference to utility routines that are used by <br />the GUI builder but are not standard X Window code (or Microsoft Windows code). Additionally, <br />2 <br />A275 07.28.94 1.05-15 Malers <br />