PropertyDefinition :: sharedData - Is data shared between instances?

Data referred to in relationships and base structures can be shared between different instances, i.e. is can be referenced from different instances.

When sharing base type data, several instances may inherit from the same base instance (e.g. when a person IS An employee in different companies, each employee instance will inherit from the same person).

If the function is not called with a valid database property definition it throws an exception.