The set from which all objects of that domain must be drawn. In SQLI, all table elements (SQLI_TABLE_ELEMENT) have a domain which restricts them to their domain set. For each data type there is a domain of the same name, representing the same set. Other domains have different set membership restrictions. Each domain has a data type, which determines the rules for comparing values from different domains, and the operators which may be used on them. The PRIMARY_KEY data type and domain is unique to SQLI. It is used to relate primary keys to foreign keys unambiguously (see SQLI_TABLE_ELEMENT)
A value in this field indicates that the domain is derived from a FileMan-specific field type. It is intended to signal vendors that a proprietary function may be required to implement the domain.