Spreadsheet Design Concepts Series
Worksheet modularisation 3 (bad)
Most significant spreadsheet based systems will have multiple worksheets. That does not mean they are modular.
This diagram from a large live model shows the model spread across many many sheets. In this case though there are so many interdependencies that each sheet could not be said to be modular. To understand any one sheet you also need to understand all those it interacts with, and those interactions are complex. this makes the model very difficult to break down and understand in manageable parts.
One important concept is 'flow', the idea that data should flow in one main direction. In the above model there were lots of conceptual circular references. eg the inputs sheet depends on the pricing sheets, and the pricing sheet depends on the input sheet. These may well be unconnected cells, so there is no physical circular reference in the formulas. But from a model comprehension point of view these circular flows need full investigation just to get a basic understanding.
25 January 2012 - UK Excel Developer Conference - London
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