This is a Conceptual Data Model for Bill of Materials, which is a hierarchical structure. This Model shows that each entry in the Hierarchy can have a 'parent' which is another entry in the Hierarchy. At the Conceptual level, which is shown below, this is indicated as a 'rabbits ear' or associative relationship. In the Physical Data Model, this is shown explicity, and is somewhat easier to understand, and here's a version for a Paper Manufacturing facility with a Warehouse

Barry Williams
Principal Consultant
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