Web Services for Loosely Coupled Systems
Two systems are considered loosely coupled if the only mandate imposed on both systems is to understand the aforementioned self-describing, text-based messages. Tightly coupled systems, on the other hand, impose a significant amount of customized overhead to enable communication, and require a greater understanding between the systems.
By using XML-based messaging as the mechanism by which the service is created and accessed, both the web services client and the web services provider are freed from needing any knowledge of each other beyond inputs, outputs, and location. A high degree of abstraction exists between the implementation and the consumption of a web service.
Loosely coupled and coarse-grained characteristics make web services very suitable for exposing high-level business functionalities, and a good distributed platform to expose a business module.