One of the most frequently asked questions on business modelling is how many levels and what should be modelled at each level. The Zachman framework gives us some basic clues on this suggesting that the higher levels should be conceptual and the lower levels physical detail. This good indicative concept sets the scene but no more.
I wish the answer had a a simple framework reply as so many students of business architecture expect "painting by numbers" templates and it takes some level of experience of delivering architecture to realise why this is not possible. I find myself replying with the dreaded phrase " It depends"! The reason is that levels relate to the output and motivation for that output and one size doesn't fit all.
Zachman gives us a clue on the rows and that is where the stakeholder audience sits to the left in many depictions. Each and every level should relate to a stakeholder alignment, in that the model at the chosen level should provide information on the relationships appropriate to the stakeholders needs. This is because business architecture is about communication and its artifacts respond to a demand for clarity and information. The "it depends" then relates to the reason for the model and the stakeholders involved.
The first stage in determining levels therefore needs to be a stakeholder analysis with the stakeholders and the communication messages defined first; this should give some indication of the nature of the levels and the number required, This also stop wasteful modelling of either items that don't add to the needs of recipient which clouds clarity, or modelling of detail for modelling detail sake i.e. stop drilling.
Further issues around modelling layer choice are about the size of the diagram and item consistency. You need levels to keep the size sensible and if having more levels allows further stakeholder segmentation of the information then that is good too. The final issue for this post is that items have to be a the same level of importance in that grouping say " Perform Strategy Planning" with " Create invoice" would be ridiculous albeit that is an extreme example but it does illustrate the point. So, if you have items of obviously different levels then you need extra levels. People get really hung up about levels but it is just common sense.