Lets look at simple example.
Following organization using different systems to achieve their day to day operations (ex- Inventory controlling , HR management , Sales monitoring ..etc). By the time this organization reach the huge market and operating as a large company.
Inventory controlling , HR management , Sales monitoring all those systems are independently operating. When the company need to use some of the data with in the two different system it will not possible with above existing system because those are tightly coupled.
Lets look at following system,
The same system once expose with defined interface to communicate with each other then the above three components act as services. Services may also be wrappers for existing Legacy systems to achieve the organization expectation.
With in the Organization system follows the global standard interface to communicate to each other then the system can expose to the out side world as well then it will improve the interoperability among organizations.