productIdentifier

indicates whether this specific product attribute is a unique identifier for a specific product instance. An example might be a "serial number" product attribute. The attribute can have one of the following values:
- "no" (D), indicates that the product attribute cannot be used to identify a specific product instance
- "primary" - indicates that the specific product attribute is the preferred attribute to use for selecting a specific product instance. When a product attribute is identified as a primary Product identifier, it must be included in the PCT.
- "secondary" - indicates an optional search key for identifying a specific product instance. When a product attribute is identified as a secondary Product identifier, it can be included in the PCT product description, but it is not required.