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user interface layer
subject			fact

user interface layer	handles the user interface
	is a subtopic of 9.5 - Architectural Patterns
	is a kind of layer
	must be independent because there will often be several different UIs for the application
	should be at the top of a multi-layer system
layer	communicates using procedure calls or by inter-process communication where the lower layers can become servers and the higher layers can become clients
	has example The set of related services which could form a layer might include: Services for computation Services for transmission of messages or data Services for storage of data Services for managing security Services for interacting with users Services provided by an operating system Services provided directly by the hardware
	has well-defined interface that is used by layer immediately above
	is often divided into smaller subsystems
	is part of multi-layer system
	only communicates with the layer immediately below it
	sees a lower layer as a set of services it can use
	usually provides services through an API
component	may perform a special-purpose function such as the user interface for a particular system