Semantic Integrity

Semantic integrity ensures that data entered into a row reflects an allowable value for that row. The value must be within the domain, or allowable set of values, for that column. For example, the quantity column of the items table permits only numbers. If a value outside the domain can be entered into a column, the semantic integrity of the data is violated.

The following constraints enforce semantic integrity:

• Data type

  The data type defines the types of values that you can store in a column. For example, the data type SMALLINT allows you to enter values from -32,767 to 32,767 into a column.

• Default value

  The default value is the value inserted into the column when an explicit value is not specified. For example, the user_id column of the cust_calls table defaults to the login name of the user if no name is entered.

• Check constraint

  The check constraint specifies conditions on data inserted into a column. Each row inserted into a table must meet these conditions. For example, the quantity column of the items table might check for quantities greater than or equal to one.

For more information on how to use semantic integrity constraints in database design, see the IBM Informix: Database Design and Implementation Guide.