Database constraints and validity checks are sometimes loosely referred to as business rules (see Semantic Data Integrity Constraints and Semantic Constraint Specifications). They define conditions that must be met before a given value is permitted to be written to a column such as value ranges, equality or inequality conditions, and intercolumn dependencies. Teradata Database supports constraints at both the column and table levels. Constraints are defined using the CREATE TABLE and ALTER TABLE SQL statements.
Database triggers, too, are often referred to as business rules. They define certain actions that are to be taken when a particular condition occurs during the update of the table on which they are defined.
- Lists all constraints, triggers, and validity checks defined for a database.
- Provides input to the Table form.
This form supports the second step in the ATM process (see Goals of the ATM Process).
Information Recorded on the Constraints Form
The Constraints form records the following information about each constraint, trigger, and validity check.
|ELDM Page||Page of the Extended Logical Data Model to which this constraint pertains.|
|System||Name of the business system in which the applications using this constraint are defined.|
|Constraint Number||The number that applies to this constraint. This number is used by other forms as a “foreign key” value to refer to the constraints defined by this form.|
|Constraint Description||Full text description of the constraint.|
|NC||No changes permitted|
|ND||No duplicates permitted|
Example: Contraint Codes
Page: ___ of: ___
ELDM Page: _____
|Constraint Number||Constraint Description|
|001||ND, NN, NC, PK|
|002||Must be greater than zero (whole positive integer)|
|003||Mutually exclusive: One required|
|004||Mutually exclusive: All required|
|005||No recursion and no loops|
|006||Excludes Saturdays, Sundays, and legal holidays|
|007||Prevent delete rule|
|008||Reassign delete rule|
|009||Nullify delete rule|
|010||Cascade delete rule|
|011||Copy rows to History table before deleting|
|012||Trigger update to OrderPart Category table on insert to Order or Part tables.|