Business Data Diagram (BDD) defines the structure of how data is thought of in a business. BDDs are an RML data model which show the relationships between business data objects. They show how many of one object can be related to another object (which is a cardinality), such as how many shipped products or payment types an order can have. BDDs look similar to entity relationship diagrams (ERDs), but BDDs are actually conceptual data models that show business data objects from a business user perspective, while ERDs show the implementation of data objects in a schema.
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Learn more about requirements models in our book Visual Models for Requirements. (See Chapter 19 for Business Data Diagrams)