Layered Architecture, AKA n-tiered

• probably the most popular
• It is simple, easy to learn, and fits into Conway’s law
• Conway’s law: companies design architectures mirroring their communication systems.
• The most common tiers are presentation, business, persistence, and database.
• When no one develops the solution architecture, the design converges into n-tiered.
• The layers can be Closed or Open
• Closed Layer: The request comes from the presentation and should go through all the layers
• Open Layer: Allows to skip a layer (sometimes used when the code only has a call to the next layer; sinkhole anti-pattern)
• Shared or Common Code usually belongs to an Open Layer
• It is common to see classes with names like “CustomerBusiness, CustomerDao”
• It belongs to monolithic architectures, with low; elasticity, fault tolerance, modularity, scalability, and testability.