Single-Level Bill of Material
Definition
A single-level bill of material lists only an item's immediate components (one level down) with quantities per parent, serving as the building block from which multilevel product structures are assembled.
In Practice
ERP systems store BOMs single-level: the finished item's bill lists its direct subassemblies and parts, each subassembly has its own single-level bill, and the multilevel structure is generated on demand by chaining them. This modularity is what keeps maintenance sane, when a bracket changes inside a motor subassembly, only the motor's single-level bill is edited, and every product using that motor inherits the change automatically.
Single-level bills are also the natural view for execution: a work order to build the motor needs the motor's direct components, not the whole product tree. Cost roll-ups, backflushing, and where-used queries all run off the network of single-level parent-child links.
Frequently Asked Questions
Why do ERP systems store BOMs as single-level structures?
Modularity. Each parent-child relationship is stored once; multilevel and indented views are computed by chaining single-level bills. An engineering change to a shared subassembly is made in one place and propagates to every product that uses it, impossible if each product carried its own full flattened structure.
When is a single-level BOM view used?
In execution and maintenance: a production order picks and backflushes against the parent's direct components; engineering edits one level at a time; costing rolls up level by level. The full multilevel or indented view is for analysis, understanding structure, lead-time stacking, and total component content.
Related Terms
A multilevel bill of material is the complete product structure showing every level of assembly (from the finished item through subassemblies down to purchased components and raw materials) with quantities linking each parent to its children.
Indented Bill of MaterialAn indented bill of material is a multilevel BOM display that shows the product structure hierarchically, indenting each level so parents, subassemblies, and components appear in their true structural relationships.
Where-Used ListA where-used list is a report showing every parent assembly and product in which a given component appears, tracing the bill of material upward, the reverse of a BOM explosion.
Low-Level CodeA low-level code is a number assigned to each item identifying the lowest level at which it appears in any bill of material, used by MRP to ensure an item's requirements are fully accumulated before its needs are calculated.