Support defining attributes as having domains. Support definition of composite domains. Support definition of operations between domains, e.g., calculations of time and money. This is also the heading of the table. Each attribute in the schema is the name of a role played by a domain in the schema.
Attributes are unordered the columns are unordered.
Values in a tuple are atomic no composite or multivalued attributes allowed in implementation. No duplicate tuples. In order to specify precisely which attribute one means, you can qualify the attribute name by prefixing the table name. There may be more than one field or combination of fields that are unique identifiers. It contains the minimum number of fields necessary to make a unique key.