Creating/Defining Your Data Model › Defining Your Data Model › Relation Sequencing

Relation Sequencing

CA 2E uses default sequence order for relations. You can override the default sequence by entering different sequence numbers into the Seq column of the Edit Database Relations panel.

The default order and sequence of relations is as follows:

The two levels of sequencing are key level and attribute level. You cannot sequence key relations after attribute relations. If you use the same sequence number on different relations within the same level, the order of these relations follows the default ordering.

Sequence numbering follows the collating sequence order of importance. Blank is first, followed by 1, 2, 3, and so on.

Note: You can add sequence numbers after all relations for the file have been entered. Blank sequence numbers come before numbered sequence numbers.

The Refers to relation for involuted relations should appear after all other relations on the file if virtual fields are to be specified for the relation.

The sequence number you use may have some consequence when you later add virtual fields to a file that references itself.

CA 2E expands the relationship based on which file entries are known at the time the relation is resolved. If a field is to be virtualized but has not been expanded or is not known to the file, the field cannot be virtualized.

For example, Employee Refers to Department and Employee Refers to Employee For Manager. If Department Name is virtualized from Department and Department Name is also desired for Manager's Department, the Employee Refers to Department relationship must be sequenced before the Employee Refers to Employee For Manager relationship.

A file-to-file relationship is expanded to place the fields that are the key of the related file on that file. In the above example, if Department is keyed by Department Code, the relationship Employee Refers to Department is expanded to show the Department Code as a foreign key on the Employee file. Department also has an attribute of Department Name that is to be virtualized onto the Employee file. Upon expansion of the relationships, the virtual fields create file entries. As a result, when the Employee Refers to Department relationship is expanded, the virtual field Department Name also becomes a file entry for Employee.

When the relationship Employee Refers to Employee For Manager is expanded, the key of Employee is another file entry such as Employee Code. For this relationship, you want to virtualize the field Department Name of the manager. Expanding the relationship Employee Refers to Employee For Manager will also include another field: Department Name for Manager.

If the Employee Refers to Employee For Manager relationship is expanded before the Employee Refers to Department relationship, the virtual field Department Name for Manager is not known as a file entry and will not be expanded as a virtual field.

For more information about:

• Procedures, see the chapter on Relation Sequencing.
• Virtual fields, see the chapter "Maintaining Your Data Model."