My third law is not so much of a law as a principle and is about architectural modelling. Models are all about complexity simplification and communication and so architectural models should be based around differing levels of abstraction for simplification and views for communication. Thus my third law is
Large projects are best managed using a set of abstractions and views or Architectural Framework.
There are normally three levels of abstraction (conceptual, logical and physical) and a number of views (Business, Technology etc) dependant on the number of stakeholders in the project.
The abstractions provide complexity management and simplification, the views or perspectives provide a communication and collaboration structure.
I met the CEO of a multinational manufacturing company and he said that he thought of architecture as giving him a Rubik’s cube of his organisation; sets of independent elements with different perspectives at different levels of abstraction. This allowed him to switch elements in and out of his organisation at will rather than having one large and unchangeable mass. I thought this was an interesting perspective (sic) on the third law.
Some time ago I wrote a paper on this which, whilst old, is probably still valid. It had three levels of abstraction and 4 views (business, application, information and technology). If I was to rewrite this paper I would probably say that the number and type of views is variable and dependant on the number of users of the Framework.
There are a huge number of different frameworks such as Zachman,
I think I’m all lawed out now!