Entities are simply formed by grouping Attributes together. One or more Attributes are shared between two or more Entities. According to the AtomicDB terminology, shared attributes are called bridge concepts and this is the equivalent of the relationship that is implemented with primary and foreign keys on two tables but here we are completely independent to mix and match them. For example PartColor, could be merged with another attribute from a different table in another relational database. … Atomic Information Resource Data Model (AIR)