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--- concepts:views [2009/10/27 00:15]
shona.weldon
+++ concepts:views [2009/11/05 13:41]
shona.weldon
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 ====== Views ======
+A dynamic and flexible way to extend a model, views are a powerful tool in the whatIf? suite.
-The power of views is that they are a dynamic and flexible extention to an otherwise resonably static and rigid model.  Models, especially once populated with data are pretty ridgid, changing the design and reloading data.  Views provide a mechanism for extending the model either through preprocessing input data or additional analysis of output data.
+Models, especially once populated with data, are fairly rigid. Modifying any working model requires changing the design and reloading data.  Views provide a mechanism for extending the model either through preprocessed input data, additional analysis of output data and even implementing feedback loops in the model's logic.
-One example of using a view to extend a model is writing a view which builds a control variable which ha
+==== Example 1: Extend a model by changing input data ====
-The model is a rigid structure views add a layer of flexibility to that...
+Suppose you had a model which had a control variable specifying exogenously the market share for new vehicles over time.  There are many ways to create that data and one must have been used to load the original model.  If you found a new algorithm for determining that market share based on something inside the model, something totally external or some mix of these, then a view could be written to implement this algorithm and feed it into the model as the new market share.  Essentially you have extended the model's scope but have taken on the work of actually modifying the model.  Of course the model can be changed later to encapsulate the new logic in the model itself but it doesn't need to.
+==== Example 2: Implementing feedback ====
+Supp
+Part of the design process is deciding what should be part of the rigid structure of the model and what should be dynamic and implemented by views.
 In the whatIf? platform views are the method used for interacting dynamically with the model.  Views are used to import and export data, to mediate interaction with the model, do analysis and display it to the user, do iterative runs of the model to converge on parameter settings and every combination of these.

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