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<br />e <br /> <br />e <br /> <br />e <br /> <br />< ,~_:~"_",,,,:,;.,i:, <br />JJtJ~~S3 <br /> <br /><,"' <br /> <br />Functional Specification for the Planning Model <br /> <br />The model should be an effective tOill for making in-depth studies of <br />the central problems which motivated its development. <br /> <br />The model should be a flexible tool for examining a wide range of <br />impacts of the central problems viewed from different perspectives. <br /> <br />5. The model should be easy to understand and to operate. <br /> <br />3. <br /> <br />4. <br /> <br />6. To the extent possible, the model should detect user errors. <br /> <br />These design objectives arise directly from the nature of the planning process and the <br />variewof groups who are interested in having access to the model. There are inevitably <br />tradeoffs among the objectives, To achieve consistency, stability and robustness, the flexibility <br />to define arbitrary network configurations must be given up. To maximize useful flexibility, <br />the user must accept complexity in the model, which conflicts with ease of use. To maximize <br />ease of use, resources must be diverted from detailed development of data and refinement of <br />the Baseline assumptions. <br /> <br />The user interface design proposed herein is intended to make the best use of project <br />resources and to strike the most appropriate balance in supporting those activities that will give <br />the model the greatest utility to the end users. These areas of support and the interface features <br />that will provide the support are discussed below. <br /> <br />Support for Determining Underlying Data and Assumptions in the Baseline <br /> <br />The basic procedure for using the model will be to specify scenarios that differ in <br />particular respects from the Baseline and to compare the output from model runs. In order to <br />decide what changes in Baseline assumptions and data would correctly represent a hypothetical <br />situation, the user must be able to determine exactly what assumptions are reflected in the <br />Baseline. . <br /> <br />Information that is conceptually complex or unchanging, such as the general rules <br />represented in the model for the operations of reservoirs, will be presented most effectively in <br />the model's printed documentation. Other types of information, such as point-specific data <br />which can be expressed concisely or which may be modified by the user as part of the <br />definition of a scenario, should be available to the user both in the printed documentation and, <br />upon request, within the user interface. Still other types of information, such as a list of <br />scenarios which the user has defined and saved, can only be made available to the user through <br />the user interface. <br /> <br />A firm design criterion for the Planning Model is to make all essential data, such as arc <br />capacities or ranks which can be modified by users to define new scenarios, easily 'accessible <br />through the user interface. In addition, a design objective for the Planning Model will be to <br />make as much supporting information as possible accessible through the user interface. <br />Supporting information might include the total irrigated acreage represented by each <br />agricultural demand in the Baseline or the exact definition of the aggregated tributary areas for <br />each inflow point represented in the model. <br /> <br />Finally, a design objective which will be kept in view during the programming design <br />and implementation phases of the project, will be to provide support for users to modify <br />assumptions in the Baseline by modifying factors used in the derivation of Baseline data, as an <br />alternative to modifying the data directly. The basis for this objective is the recognition that <br />refinements in basic data are expected during the lifetime of the model and that the model's <br />usability would be enhanced if, for example, demands could be manipulated in terms of such <br />factors as acreage and efficiency, or if inflows could be modified in terms of unit runoff <br /> <br />17 <br /> <br />"- --",',' <br />k--__"'_Ji~-;~. ~;; ,:t~~:.-.;i;1 <br />