Component Definitions

This panel enables you to define parameters of the CREATE TABLE command for a component of the Entity or Relationship.

All the options that are written in capital letters refer to keywords of the CREATE TABLE command. For full details please see your SQL language reference manual.

Components (attributes) of Entities and Relationships are transferred to columns in tables. For this purpose each attribute is identified by the name of the attribute and the name of the parent Entity or Relationship.

NULL Constraint enables you to specify if a column can contain nulls. If you choose None then the column can contain nulls by default. If you choose NULL then the column can contain nulls. If you choose NOT NULL then the column cannot contain nulls. To satisfy this constraint, every row in the table must contain a value for the column.

Datatype represents the datatype of the column. Either type the name of a datatype in the text field or click on the Select button to select a datatype from a list of available types. The types available depend on the SQL dialect that you have chosen.

DEFAULT specifies a value to be assigned to the column if a subsequent INSERT statement omits a value for the column. The datatype of the expression must match the datatype of the column.

CHECK  specifies a condition that each row in the table must satisfy.

CONSTRAINT  defines an integrity constraint. An integrity constraint is a rule that restricts the values for one or more columns in a table.Remember that all the constraints that are inherent to the Information Model, such as primary keys and referential constraints for the foreign key are automatically generated by Data Base Designer. Use this field to define any additional constraints that may be needed.