What is a Loosely Coupled System?

In a loosely coupled system (e.g. Service Oriented Architecture i.e. SOA), the dependencies can be either a Real Dependency or an Artificial Dependency.

Real dependencies are the services that you need to fulfil your need, this is something that cannot be eliminated or reduced.

Artificial dependency on the other hand are the features you need to adhere to in order to consume the services you need. Typically these fall in the categories of platform dependencies, API dependencies, language, etc. Although artificial dependencies cannot be eliminated it can be reduced.

A loosely coupled application is on that minimise its Artificial Dependency.