Keys (PDM)

A key is a column, or a combination of columns, that uniquely identifies a row in a table. Each key can generate a unique index or a unique constraint in a target database.

The physical diagram supports the following types of keys:

Example

The TITLE table shown below has a primary, alternate and foreign key:

• TITLE_ID is the primary key and consists of the column TITLE ISBN which identifies each book title in the table

• TITLE_NAME is an alternate key containing the columns TITLE NAME and TITLE TYPE. It allows each title to be identified by its name and type, The fact that it is an alternate key indicates that there is a constraint that no two titles of the same type can have the same name

The TITLE table also contains the foreign key column PUBLISHER ID. This column references the primary key column in the Publisher table.

• Creating a Key
  The method for creating a key depends on the type of key. See the appropriate section:
• Key Properties
  To view or edit a key's properties, double-click its Browser or list entry. The property sheet tabs and fields listed here are those available by default, before any customization of the interface by you or an administrator.
• Primary Keys
  A primary key is the primary identifier for a table, and is attached to one or more columns whose values uniquely identify every row in the table. Every table must have a primary key, composed of one or more of its columns.
• Alternate Keys
  An alternate key is a key attached to one or more columns whose values uniquely identify every row in the table, but which is not a primary key. An alternate key can also be a foreign key. Each alternate key can generate a unique index or a unique constraint in a target database.
• Foreign Keys
  A foreign key is a primary or alternate key that migrates from another table. Depending on selected model options, a primary key can be automatically migrated to a child table as a foreign key at reference creation.
• Adding Parent Table Columns to a Key
  You can add additional columns from the parent table to a primary key or an alternate key.
• Naming Key Constraints
  Naming key constraints helps you to identify and customize key constraints in scripts for database creation and modification. The constraint name gives you greater flexibility for modifying keys in subsequent database generations.