[1] For example: For the relational model it is a requirement that each part of a tuple be atomic.
[2] The consequence is that each value in the tuple must be of some basic type, like a string or an integer.
For the elementary type to be atomic it cannot be broken into more pieces.
Alas, the domain is an elementary type, and attribute domain the domain a given attribute belongs to an abstraction belonging to or characteristic of an entity.
[clarification needed] For example, in SQL, one can create their own domain for an attribute with the command The above command says: "Create a datatype SSN_TYPE that is of character type with size 9".