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Methods for Processing Disk Files
Random-by-Key Processing
For the random-by-key method of processing, a search argument that identifies the
key of the record to be read is specified in factor 1 of the calculation specifications
for the CHAIN operation. Figure 151 on page 300 shows an example of an
externally described DISK file being processed randomly by key. The specified
record can be read from the file either during detail calculations or during total cal-
culations.
The random-by-key method of processing is valid for a full procedural file desig-
nated as an input file or an update file.
For an externally described file, position 34 of the file description specification must
contain a K, which indicates that the file is processed according to an access path
that is built on keys.
The data description specifications (DDS) for the file specifies the field that contains
the key value (the key field). Position 35 of the file description specification must be
blank.
A program-described file must be designated as an indexed file (I in position 35),
and position 34 of the file description specification must contain an A, D, G, P, T, or
Z. The length of the key field is identified in positions 29-33 of the file description
specification, and the starting location of the key field is specified on the KEYLOC
keyword. Data description specifications must be used to create the access path for
a program described input file (see “Indexed File” on page 288).
Example of Random-by-Key Processing
The following is an example of how to use the random-by-key method of proc-
essing data. Figure 144 on page 294 and Figure 150 show the data description
specifications (DDS) for the physical files used by EMSTUPD ( Figure 151 on
page 300).
A*****************************************************************
A* RELATED PGMS: EMSTUPD *
A* DESCRIPTIONS: This is the DDS for the physical file CHANGE. *
A* It contains one record format called CHGREC. *
A* This file contains new data that is used to *
A* update the EMPMST file. *
A*****************************************************************
A*
A R CHGREC
A ENUM 5 0 TEXT('EMPLOYEE NUMBER')
A NNAME 20 TEXT('NEW NAME')
A NTYPE 1 TEXT('NEW TYPE')
A NDEPT 3 0 TEXT('NEW DEPARTMENT')
A NNHRS 3 1 TEXT('NEW NORMAL WEEK HOURS')
A K ENUM
Figure 150. DDS for database file CHANGE (physical file)
EXAMPLE PROGRAM:
In this example, the EMPMST file is defined as an Update
Full-Procedural file. The update file CHANGE is to be processed by keys. The DDS
for each of the externally described files (EMPMST and CHANGE) identify the
ENUM field as the key field. The read/update processes are all controlled by the
operations specified in the Calculation Specifications.
Chapter 16. Accessing Database Files 299