A B/M (standing for Bill of Materials) usually has two master data, item master and product structure master. But a Bill of Materials showing the relationship between parent items and child items cannot be generated by only this data, something connecting these two masters is necessary. To make a Bill of Materials, two connections with items and the product structure are usually required: one is the connection to search one's child(ren), or lower-level item(s), another is the one to search one's parent(s), or upper-level item(s). The former is generally called "Chain", while the former "Where-used Chain".

Chain means the connection with items and the product structure to show what (lower-level) items an item consists of. In the B/M shown in the figure, the lower-level items of Product X are a and b, and Item X and Product structure X-a, X-b are connected as Chain. Item a is also connected with Product structure a-"イ". In this way, the connections to search one's own child(ren) are made for other items.

Related term: Bill of Materials,Where-used Chain