This part of ISO 23584, on the basis of the rules set forth in ISO 13584-42, ISO/IEC Guide 77-2 and IEC 61360-1, specifies a reference dictionary of standardized product properties for the area of optics and photonics. The properties are determined on the basis of standardized attributes. To ensure optimum unambiguity, the standardized properties are classified into definition classes forming a so-called standardized “reference hierarchy”.