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Review the explanatory note for establishment saying only one service, which is really about how the statistical structure is generated. It mainly has to do with having one NAICS code associated with an establishment for statistical purposes, not necessarily limiting an establishment to a single offering.
Need to think more about the relationship between an establishment and an enterprise – where an establishment could potentially be part of more than one enterprise depending on how the accounting works, so potentially we need a new property to represent that relationship rather than isPartOf, although there is a hierarchical relationship between an establishment and an enterprise.