Single- versus Multi-Table Relationships 

A sibling relationship always relates main table records. By contrast, a parent/child relationship can relate records within a single table or between any two tables. Specifically, it can do the following:

●      Relate records within the products of the main table (for example “products and accessories”)

●      Relate between records of the main table and non-main table records of a subtable in either direction (for example “kits and parts” [main ® subtable] or “bundles and products” [subtable ® main])

●      Relate records within the non-products of a single subtable (for example “parts and subparts”)

●      Relate between non-main table records of one subtable and non-main table records of a different subtable (for example “interchange part number groups”).

The figure below illustrates two parent/child relationships between tables: a “bundles and products” relationship and a “kits and parts” relationship.

From a relationship-centric standpoint, a parent/child relationship represents a single relationship among a set of related records. By contrast, from a product-centric standpoint, a parent/child relationship within a single table (for example, main/main or subtable/subtable) in effect represents two distinct relationships for each record: (1) the “parent” relationship of the parent/child relationship in which the record is the parent (looking “down” at its children); and (2) the “child” relationship of the parent/child relationship in which the record is one of the children (looking “up” at its parent).