I know it probably sounds like very trivial question but I couldn't find any resources on the internet.
Could you please tell me what are open and closed layered architectures and why open layered architecture is apparently more difficult to maintin? Are there any disadvantages of using closed/open layered architectures?
A closed layered architecture means that any given layer (or tier) can only use the services of the next immediate layer, whereas in an open layer architecture a given layer can make use of any of the layers (or tiers) below it. Closed layer architecture promotes independence between layers by reducing dependencies.