Separate a company-database item master into a shared product definition and legal-entity released products, and unpick item groups that carry posting and reporting meaning at the same time.
Product data feels like the least conceptual workstream on a migration. It is a list of things the business sells and buys, it has a primary key, and everybody agrees what an item is.
Work through the source item record attribute by attribute and assign each to a target layer. The layers, and what belongs in each:
Because each company runs in its own database, item coding never had to agree. Estates therefore contain three patterns, often simultaneously:
Source item groups commonly serve posting and reporting simultaneously. The concept mapping records this directly — item groups are often overloaded for reporting and posting, and the target may split that intent.
Source estates express product variation through item coding: a base code with a suffix for colour, size, pack or grade. That convention is evidence of how somebody organised a list, not evidence of how the business operates.
Units of measure load in the first canonical wave, before products, and they are cheap to get wrong in ways that surface late.
User-defined fields on the item master are one of the most common extension patterns in this estate, and one of the most commonly overlooked in product design. They hold classification, supplier data, compliance attributes, dimensions, certifications, and whatever else somebody needed once.
Units of measure and conversions — first wave, before products exist. Product dimension, storage and tracking groups; item model groups; item groups; product categories — configuration, before any product record. Shared products, from the identity-resolved catalogue.
One source item record supplies several target layers — shared product, released product, dimension groups, item model group, item group, category and warehouse item. Item identity across company databases is a business decision that must precede the shared-product design. Item groups usually do two jobs.