ENFORM User's Guide

Connecting Record Descriptions to Form New Relationships
Developing an ENFORM Query
3–12 058058 Tandem Computers Incorporated
Figure 3-7. Diagram of LINK OPTIONAL Where Employee is Linked to Region
Employee Record Occurrences
empnum
1
23
32
43
• • •
343
empname
ROGER GREEN
JERRY HOWARD
THOMAS RUDLOF
PAUL WINTER
• • •
ALAN TERRY
Logical Records
1
23
32
43
• • •
343
1
43
• • •
343
empnum manager regname
HEADQUARTERS
GERMANY
• • •
CANADA
ROGER GREEN
JERRY HOWARD
THOMAS RUDLOF
PAUL WINTER
• • •
ALAN TERRY
empname
LINK OPTIONAL
Appears to Create
New Logical Records
Region Record Occurrences
manager
1
29
43
• • •
343
regname
HEADQUARTERS
EAST
GERMANY
• • •
CANADA
Session-Wide Links and the WHERE Clause
When your query specifications contain a WHERE clause, ENFORM uses any request
qualifications specified in the WHERE clause to produce the target records (the
records from which your ENFORM output is produced). ENFORM takes the logical
expressions specified in your WHERE clause and converts them into conjunctive
normal form. This means that ENFORM converts the logical expressions into one or
more “terms”. These “terms” consist of logical expressions that are connected to other
logical expressions by the boolean operator AND. Each “term” can have “subterms”
that are connected by the boolean operator OR. Note that what appears as a “term” in
your WHERE clause might not be the same as a “term” in the converted WHERE
clause. Refer to Appendix D of the ENFORM Reference Manual for more information
about the “terms” of a WHERE clause.