Page 235 - DCAP307_PLANNING_AND_MANAGING_IT_INFRASTRUCTURE

Unit 14: Enterprise Architecture

14.2.8 Layered Notes

This architectural style is suitable for applications that involve distinct classes of services that
can be arranged hierarchically. Often there are layers for basic system-level services, for utilities
appropriate to many applications, and for specific tasks of the application. To date, the layered
architectural pattern has been used mostly to model message-passing situations. But this
architectural style has the capabilities to model other kinds of problems, for which it is not
generally used. Almost all architectural representations of the pipeline style and the main
program and subroutines style can be modelled by a layered style. So obviously the Block
Builder system can be modelled as a layered architecture.

The strict layer structure as explained above is not too useful. But, by introducing some flexibility,
the layered structure can be used to model many software systems.

Example: We might allow the layers to be transparent, i.e. interfaces from the lower
layers show through as opaque so that only the interface defined by a layer can be used by the
next layer up.
We can also define the method of interaction between processes in the same layer. In a strict
layering model the components in the same layer cannot communicate, while in a lenient
layering model such communication is allowed.

Figure 14.6: Block Builder as a Layered Architecture

Input
File

Sentence Builder
red create
input a
line sentence
Layer 1

Sentence Evaluator
evaluate
a
sentence
Layer 2

Block Tree Bulider
check build
sentence block
type tree
Layer 3

Block Code Displayer
display
block
tree
Layer 4

Source: http://etd.lsu.edu/docs/available/etd-07082004-152330/unrestricted/Banerjee_thesis.pdf
We can also apply constraints on the direction of inter-layer communication direction. In a strict
scheme, the inter-layer communication is unidirectional, while in a lenient scheme such

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