Large Scale Design

Learn about large-scale design!

characteristics of large scale design

usually cross responsibilities within an organisation, typically cross organisations

how do the issues change with scale?

as scale increases, the number of people affected by decisions increases, often non-linearly

object level (small and medium scale)

getting the algorithms and data structures right, worrying about method signatures and visibility

micro level (small and medium scale)

combinations of a few objects

macro level - component frameworks (small and medium scales)

combinations of objects covering fairly large abstractions

application level - sub systems (larger scale)

emphasis on a “good fit” to a specific task

system level (larger scale)

integrate different applications, innovation gets more risky, changes propagate

enterprise level (large scale)

an organisation’s entire IT support, changes affect the organisation’s economics

global level (larger scale)

cooperation between organisations, interoperability, policy and security

what do strong cohesion and weak coupling look like in small and medium scale design?

single function and loose dependencies

difficulty with large scale

elements aren’t orthogonal - functions should be accessible through the UI and through scripting

what orthogonalities are present?

multiple different UIs, multiple automation routes, shared functionality between applications

what is the ideal decomposition?

one that maximises orthogonality while allowing interaction

application architecture

defines how smaller parts fit together and relate to each other, lives within a system architecture

what issues must each level balance?

ease of extension and optimisation, change and maintenance, use and reuse

application architecture principle 1

identify the components of each application

application architecture principle 2

define interfaces and stick to them

application architecture principle 3

stress consistency of UI, behavior, representation, etc