DL/I and CA IDMS/DB › Secondary Indexing (Index Databases) › Defining Secondary Indexes

Defining Secondary Indexes

Secondary indexes are defined in a manner similar to HIDAM index databases. Related statements must be included in both the index DBD and the associated physical DBD.

Sample DBD Definitions

The sample below shows the DBD definitions for a physical HDAM database (DB2) and an associated secondary index database (DBINDX2).

 DBD      NAME=DB2,ACCESS=HDAM,
               RMNAME=(GLDHDC20,5,660,850)
 DATASET  DD1=DBHDAM,DEVICE=3350,BLOCK=2048,SCAN=1
 
 SEGM     NAME=SEG1,PARENT=0,BYTES=15
 
 FIELD    NAME=(FIELD1,SEQ,U),BYTES=5,START=1
 LCHILD   NAME=(SEG6,DBINDX2),PTR=INDX
 XDFLD    NAME=XDFLD1,SEGMENT=SEG2,
               SRCH=FIELD2,DDATA=FIELD3
 
 SEGM     NAME=SEG2,PARENT=SEG1,BYTES=25
 
 FIELD    NAME=(FIELD2,SEQ,U),BYTES=5,START=1
 FIELD    NAME=(FIELD3),BYTES=10,START=6
 SEGM     NAME=SEG3,PARENT=SEG2,BYTES=15
 FIELD    NAME=(FIELD4,SEQ,U),BYTES=10,START=1
 SEGM     NAME=SEG4,PARENT=SEG2,BYTES=30
 FIELD    NAME=(FIELD5,SEQ,U),BYTES=20,START=1
 DBDGEN
 FINISH
 END



 DBD      NAME=DBINDX2,ACCESS=INDEX
 DATASET  DD1=INDX2,DEVICE=3350,BLOCK=23,
               RECORD=88,SCAN=1
 
 SEGM     NAME=SEG6,PARENT=0,BYTES=15
 
 FIELD    NAME=(FIELD6,SEQ,U),START=1,BYTES=15
 LCHILD   NAME=(SEG1,DB2),POINTER=SINGL,INDEX=XDFLD1
 DBDGEN
 FINISH
 END

Figure 15. DBD definitions for a physical and secondary database

Index DBD Statements

The index DBD must contain the following statements:

• DBD statement ── ACCESS parameter must specify INDEX.
• SEGM statement ── Defines the index pointer segment as the root for the index database. Only one SEGM statement is allowed.
• FIELD statement ── Defines the sequence field for the pointer segment. Only one FIELD statement is allowed.
• LCHILD statement ── Identifies the target segment and the physical DBD in which it is defined. The INDEX parameter specifies the name of the indexed field (XDFLD) in the associated physical DBD. Only one LCHILD statement is allowed.

Physical DBD Statements

The physical DBD must contain the following statements:

• DBD statement ── ACCESS parameter must specify HISAM, HDAM, or HIDAM. While it is possible to set up a secondary index for a logical database (ACCESS=LOGICAL), it is not recommended for reasons of performance and data independence. HSAM databases are restricted to sequential access.
• LCHILD statement ── Identifies the pointer segment and the index DBD in which it is defined. The PTR (pointer) parameter must specify INDX (for index). The LCHILD statement must be included under the SEGM statement for the target segment.
• XDFLD statement ── Identifies a source segment and its index field. The value for the NAME parameter is referenced in the LCHILD statement in the index DBD. The SEGMENT parameter specifies the source segment. The SRCH parameter specifies the sequence field in the source segment to be used for indexing. The DDATA parameter specifies a data field in the source segment to be used for indexing.

  Note that the values for the SRCH and DDATA fields will be concatenated to produce the actual index-key field values. The XDFLD statement must be included under the SEGM statement for the target segment.