Pathmaker Programming Guide

Creating a DB Requester Application
Pathmaker Application Development Overview
3–32 067868 Tandem Computers Incorporated
You cannot mix the ordering (ascending or descending) of the columns of a
primary key or index.
A primary key has uniform ordering if all the columns of the table’s primary
key have the same ordering.
A unique index has uniform ordering if all the columns of a unique index have
the same ordering.
A nonunique index has uniform ordering if all the columns of the index and
all the columns of the table’s primary key have the same ordering.
An index cannot include a column that accepts null values.
No other columns are efficient keys.
Rules for Determining Efficient Access Fields
The rules the Pathmaker product follows to mark efficient access fields for a DB
requester are:
Rule 1 For a single-file DB requester, or for the outermost parent, the first column of
every efficient key is an efficient access field if it is displayed.
Rule 2 For a child joined to a parent on an efficient single column key, the join
column is an efficient access field.
Rule 3 For a child joined to a parent on the first column of an efficient multicolumn
key, the second column is an efficient access field if it is displayed. Because
you could have several efficient multicolumn keys that begin in the join
column, you could have several efficient access fields of this type.
No other columns are efficient access fields.
Examples illustrating each of these rules are on the following pages.
Rule 1: Outermost Parents. For a single-file DB requester or for an outermost parent, the
first column of every efficient key is an efficient access field if the column is displayed.
In a multifile DB requester, tables and views are joined through a join field in parent-
child relationships. If you have joined three tables together, where A is the parent of B
and B is the parent of C, then A is the outermost parent of the three tables. If only two
tables are joined together, where A is the parent of B, A is the outermost parent.
DB requesters that access only one table are called single-file applications.
Rule 1 applies equally to outermost parents of multifile applications and to single-file
DB applications.