# Low Level Code Generation Process (PARTS.P4)
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The PARTS.P4 procedure updates the low level code field in the Parts file. Low level codes are used by MRP and cost rollup procedures, and define the lowest level in the product structure where a given part is referenced.
Frequency of Use
Low level codes are updated automatically as changes are mode to the bill of material records with BOM.E . PARTS.P4 usually only needs to run after loading bill of material data from an external source, such as when converting data from another system.