Rapid Application Development / Advanced Excel Development

Basic design (N-tier)

The core components of most significant models are:

• The inputs - either manual, system based or a mix
• Reference data - non model specific data such as interest rates, overhead rates, concrete strength etc
• Logic - The combination of inputs, reference data and business rules
• Reports - presentation of the results of the logic element

Sometimes these elements gets combined - that often leads to hard to maintain/adapt models

As well as the core model there should also be a support structure of standard components that ease the working with, maintenance of, and management of the model. These are:

• Assumptions that underpin the model, eg that inflation stays within a boundary, that results are cyclical etc.
• WorkbookStructure is an index of each sheet what it does and why its needed
• Accountability indicate who is responsible for different elements of the model, who checked it for correctness, how and when, and to what level of assurance
• Revision history should be a fairly high level readable list of changes that have been made over time. The full minute detail of this should be recorded or available in a full source control system, or by differencing two versions. This is more of a management summary.