Source and Target Segments are Dependent Segments of Same Segment Type

Assuming an application that use the CUSTOMER database, requires direct access to receivable segments based on invoice number of RECVABLE segment. The existing structure forces us to go through the customer path to retrieve a RECVABLE segment. This can be avoided by defining a secondary index for it.

CUSTOMER database needs to be indexed in sequence by invoice number - the sequence field not of the root segment, but of the RECVABLE segment. As a result this secondary index allows to access the RECVABLE segments in invoice number sequence. In this example the source segment is RECVABLE segment (RSINVNUM is a field of this segment) and, RECVABLE segment itself is the target segment.

The CUSTDBD needs to be defined as shown below.

PRINT   NOGEN
DBD     NAME=CUSTDBD3,ACCESS=HIDAM
DATASET DD1=CUST3,DEVICE=3350
SEGM    NAME=CUSTOMER,PARENT=0,BYTES=128
FIELD   NAME=(CUSTNUM,SEQ,U),BYTES=6,START=1,TYPE=C
FIELD   NAME=CUSTNAME,BYTES=31,START=7,TYPE=C
..........
SEGM    NAME=RECVABLE,PARENT=SHIPTO,BYTES=57
FIELD   NAME=(RSINVNUM,SEQ,U),BYTES=6,START=1,TYPE=C
LCHILD  NAME=(XRECVBL1,XCSTDBD3),POINTER=INDX
XDFLD   NAME=XINVNUM,SEARCH=RSINVNUM
FIELD   NAME=RSINDATE,BYTES=6,START=7,TYPE=C
FIELD   NAME=RSPONUM,BYTES=25,START=13,TYPE=C
FIELD   NAME=RSPRDTOT,BYTES=4,START=38,TYPE=P
..........
DBDGEN
FINISH
END

The DBD for Secondary Index is as follows:

PRINT   NOGEN
DBD     NAME=XCSTDBD3,ACCESS=INDEX
DATASET DD1=XCUST3,DEVICE=3350
SEGM    NAME=XRECVBL1,PARENT=0,BYTES=57
FIELD   NAME=(RSINVNUM,SEQ),BYTES=6,START=1,TYPE=C
LCHILD  NAME=(RECVABLE,CUSTDBD3),INDEX=XINVNUM
DBDGEN
FINISH
END

The PSB required for this example is:

PRINT   NOGEN
PCB     TYPE=DB,DBDNAME=CUSTDBD3,KEYLEN=30,PROCOPT=L,
        PROCSEQ=XCSTDBD3
SENSEG  NAME=RECVABLE
SENSEG  NAME=SHIPTO,PARENT=RECVABLE
SENSEG  NAME=CUSTOMER,PARENT=SHIPTO
SENSEG  NAME=BUYER,PARENT=SHIPTO
SENSEG  NAME=PAYMENT,PARENT=RECVABLE
SENSEG  NAME=ADJSTMNT,PARENT=RECVABLE
SENSEG  NAME=LINEITEM,PARENT=RECVABLE
PSBGEN  PSBNAME=CUSTPSB3,LANG=COBOL
END

The Secondary index defined changes the apparent hierarchical structure of the database, as because when data is accessed using secondary index, the index target segment (RECVABLE) is presented to the program as if it were a root segment, even if it is not the root segment of the database.

The Figure below shows the secondary data structure for the customer database when accessed by the secondary index.

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