Enform Plus Reference Manual

Enform Plus Reference Manual—422684-001
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Links and the LINK OPTIONAL
Statement Rules
To fully understand the rules for the LINK OPTIONAL statement, you must first
understand how Enform Plus defines links. This appendix describes how Enform Plus
defines a link, reviews the rules for the LINK OPTIONAL statement, and provides some
examples of invalid links.
How Enform Plus Defines a LINK
Enform Plus recognizes links that are established in these ways:
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by a LINK statement that references both record descriptions
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by a LINK OPTIONAL statement that references both record descriptions
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by a WHERE clause containing a term that references both record descriptions
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through the transitive property of links.
The following paragraphs discuss the characteristics of these links.
Links Initiated by a LINK Statement
A link initiated by a LINK statement is a two-directional link. Therefore, a two-way
dependency condition exists between the record occurrences associated with the linked
record descriptions. For example, if you specify:
LINK apple TO orange VIA seeds;
the following is true of the logical records built for the link:
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A given apple record occurrence appears in the logical records only if its linking
field value matches the linking field value in an orange record occurrence. Thus,
an apple record occurrence depends upon an orange record occurrence.
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A given orange record occurrence appears in the logical records only if its linking
field value matches the linking field value in an apple record occurrence. Thus, an
orange record occurrence depends upon an apple record occurrence.
A two-directional link established for a LINK statement can be sketched as follows:
record-description-1 record-description-2
where the two-headed arrow indicates the two-way dependency condition.