The Data Vault Handbook - Concepts and Applications

On the other hand, Data Vault also makes use of the so-called “hard” rules. Differently from (soft) business rules, hard rules are those that don’t change the data, but just adapt the data structure to load it into the data platform. For instance, a hard rule could be the change of a data type of an attribute, or the addition of technical fields into our table.

Hard Rules Technical adjustments without altering the data’s content

Soft (Business) Rules Transform the data by adapting it from its original form to serve end-user requirements

In summary, hard rules help us to integrate and work with our data without transforming it in a fundamental way, while (soft) business rules transform the data to reach the end-user’s needed specifications. 1.3.2. BUSINESS KEYS Business keys are unique identifiers of relevant business objects, such as customer or order, enabling their identification, tracking, and location with- in a data system. Furthermore, they serve as the foundation for data integra- tion, allowing businesses to establish a common language for organizing and understanding their data. Identifying business keys involves a thorough understanding of how busi- ness users navigate and retrieve information. Analyzing business process- es, source system data, and data models also aids in pinpointing business keys. Keep in mind that a good business key should have a low propensity to change and be unique.