Assume that some transactional systems and databases such as CRM exist, a retail sales system, and other systems that keep customer information in the form of one or more tables inside their own databases. There might be multiple ways of inserting customer information, such as importing from files or data entry. And each of those systems might keep only part of the customer information that is required for that system.

This is shown in the following diagram:

As you can see in the previous diagram, customer information is stored in an inconsistent manner. There might be some customer information in the retail system that is outdated while some part of the customer information might even be missed, for example, in CRM. This is an example of customer information as reference data, because all other systems and databases require this data to work (to insert data into it or get data out of it). For this purpose, we'll keep the reference data (customer information...