This boolean attribute signals whether the number is signed or not. This attribute is currently only used for binary fields which are stored externally. Binary types 16. The attribute NAME can be used for all fields, regardless of the type of the field. Its value denotes the name of the column in the database.
Null values have special properties in relational databases.
For example, two fields both with null values are not necessarily equal. Furthermore null values are different from empty strings. Representing null values as empty elements has the disadvantage, that null values cannot be distinguished from empty strings and is therefor not used.