DL/I and CA IDMS/DB › DL/I and CA IDMS/DB Correspondences › Logical Relationships and Sets

Logical Relationships and Sets

In CA IDMS DLI Transparency, each segment in a logical relationship corresponds to one of three CA IDMS/DB record types.

Junction Record

The logical child segment is defined as a junction record that is a member of two sets. The owner of one set corresponds to the physical parent segment; the owner of the other set corresponds to the logical parent segment.

Owner and Member Records

If the DL/I physical and logical parents are the same segment, one record type is used to represent both parents. In this case, the record type is the owner of the two sets of which the junction record (equivalent to the logical child) is the member.

The junction record must always have a location mode of VIA. The VIA set is the set of which the record type for the physical parent is the owner. Note that database load procedures can override this consideration.

CA IDMS DLI Transparency requires that all logical relationships (that is, unidirectional, bidirectional virtual, and bidirectional physical) be implemented as bidirectional virtual relationships. The conversion to bidirectional virtual is transparent to an application. However, the conversion of bidirectional physical relationships requires special consideration.

Implementing a Bidirectional Physical Relationship

To implement a bidirectional physical relationship as a bidirectional virtual relationship in CA IDMS/DB, a record type is defined for each of the parent segments. Additionally, a single record type is used to represent the physically paired child segments. This record type is defined as a VIA junction record in the set owned by each of the parent record types. In bidirectional virtual terms, the junction record type becomes the equivalent of the real logical child and the virtual logical child.

DL/I Logical Relationship and CA IDMS/DB Sets

The following diagram illustrates a DL/I bidirectional virtual relationship and the CA IDMS/DB set structures used to implement it.

Figure 21. DL/I logical relationship and corresponding CA IDMS/DB sets