The art of coupling is one of the most difficult challenges within an architecture. It directly correlates with software quality criteria and influences many aspects of the software. Decisions about coupling have large impact, if they need to be revoked. Within loosly coupled systems, objects can interact but don’t know much about each other (cfg. principle of segregation). Dependencies between objects must be minimized to ensure re-utilization and minimizing the impact of change. The impact shall be local and not triggering cascades through the application (cfg. open/closed principle).
There are different types of coupling:
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- Call
One building block is directly using another one. - Creation
One building block creates another one. - Data
One building block uses another as call parameter or share the same data structure. - Time
Execution sequence of building blocks matter (cfg. race conditions). - Execution Environment
Middleware, runtime environment, processes, threads, network segments matters or hardware. - Source Code
Shared libraries or deployment artifcats.
Patterns
Patterns to resolve couplin issues can be found below: