Definition: bill of materials
The list of components that make up a system. For example, a bill of materials for a house would include the cement block, lumber, shingles, doors, windows, plumbing, electric, heating and so on. Each subassembly also contains a bill of materials; the heating system is made up of the furnace, ducts, etc. A bill of materials "implosion" links component pieces to a major assembly, while a bill of materials "explosion" breaks apart each assembly or subassembly into its component parts.
The first hierarchical databases were developed for automating bills of materials for manufacturing organizations in the early 1960s.