Business Models are Like Building Plans

Business Models help portray different aspects of a business.

Just as we would make sure that we use the correct building plan to portray a particular aspect of a building, so should we make sure that we use the correct model to portray each particular aspect of a business.

Function Model

The Function Hierarchy is the only business model that can show a business as an integrated whole. If used to describe a building it would describe each section of a building and the rooms that went to make up each section.

Process Model

Process Models are best suited to showing slices through the business but not the overall structure.

From a building point of view they can bethought of a routes through the building, for example, how to get from Reception to the Personnel Department or from the Restaurant to the Car Park in an emergency.
Many analysts make the mistake of decomposing Process Models. They mistakenly think that this is a method of providing an overall structure, whereas this approach, apart from being very expensive both in time and money, actually introduces many logic flaws. It is about as useful as trying to describe a building by describing a series of routes through the building.

DFDs and IFDs

Data Flow Diagrams (DFDs) and Information Flow Diagrams (IFDs) are very useful for showing how the interrelationship between Business Functions terms of data/information flow but actually conceal rather than reveal the overall structure of the business.
In terms of a building, IFDs can be thought of as describing the type of information that flows from room to room in the building.

Summary

Always choose the most appropriate business model to portray the relevant facet of the business.
Always start with Function Model - ALL other models are derived from this.
Read more on Function Modelling
Read more on Process Modelling
Read More on Data / Information Flow Modelling