Fujitsu UDS/SQL V2.5 用户手册
Schema DDL
Linking record types
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Example 4
In order to resolve a many-to-many relationship, it is necessary to define an auxiliary record
type. This requires the following types of set membership:
type. This requires the following types of set membership:
Figure 21: Types of set membership in the case of a many-to-many relationship
The purpose of an auxiliary record type is to link the ORDERS records with the ARTICLE
records. The link is only effected if every auxiliary record is present in each set occurrence
of the two sets. This is why membership is enforced by the AUTOMATIC option.
records. The link is only effected if every auxiliary record is present in each set occurrence
of the two sets. This is why membership is enforced by the AUTOMATIC option.
If the auxiliary records contain no valid information once they have been released from their
owner records, the link to the owner records can be retained unless the records are to be
deleted. Membership can thus be specified as MANDATORY.
owner records, the link to the owner records can be retained unless the records are to be
deleted. Membership can thus be specified as MANDATORY.
(MANDATORY AUTOMATIC)
ORDERS
ARTICLE
AUX. RECORD
TYPE
(MANDATORY AUTOMATIC)