Page 644 - ExtendSim User Guide
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618 Presentation
Hierarchy
Since it has multiple uses, the Navigator is discussed fully in the How To: Miscellaneous chap- ter. For more information, see “Navigator” on page 792.
Hierarchy
As you saw in “Introduction to hierarchy” on page 37, ExtendSim’s hierarchical capability lets you combine basic modeling constructs (such as a group of connected blocks) into a single, higher-level construct, then combine several of those new constructs into an even higher-level construct, and so forth. This process causes portions of a model, or even the entire model, to be implemented in layers, where you can drill down from the highest system level to the smallest detail. For example, the Santee River Basin model on page 8 was created using many layers of hierarchy; without hierarchy the model would be overwhelmingly complex.
The mechanism for creating hierarchical layers in ExtendSim is by building a hierarchical block, a special type of block that usually has a group of blocks nested inside it. These blocks represent a portion of the model, a subsystem or submodel. Using hierarchical blocks you can nest subsystems in an unlimited number of layers for top-down or bottom-up modeling.
☞ Top-down modeling is starting with a new hierarchical block and building a model or a series of submodels in it. Bottom-up modeling involves selecting a group of blocks within a model and making them into a hierarchical block. You can create multiple hierarchical layers from the top down or from the bottom up.
Uses for hierarchy
Although you do not have to use them as you build models, hierarchical blocks can help orga- nize models logically, make models appear more attractive, improve productivity, and enhance comprehension.
• Simplifyacomplexmodelbygroupingareasofthemodelintohierarchicalblockscontain- ing submodels. These submodels can then be reused in other models without having to reproduce all of the connections.
• Insteadofshowingallthedetail,presentamodelasafewsimplebutlogicalsteps.Toreveal the subsystems within a step, just double-click the hierarchical block.
• To increase productivity and comprehension, create a hierarchical block that represents a process element, then use it in several models that have that element in common. By chang- ing the parameters, each instance of the hierarchical block can be customized for its model.
• When developing a new model, go from the simplest assumptions to more complex ones by creating more and more levels of hierarchy. This helps structure your thinking and makes models easier to follow as they become more complex.
• Althoughhierarchicalblocksusuallycontainsubmodelsofblocks,theydon’thaveto.They can also be useful for enhancing and documenting the model, serving as popup windows that reveal pictures, text, and so forth when double-clicked. For an example, see “Help block” on page 592.
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