AS400 interview questions and answers-Part 3


1. What is logical file in AS400? What are the types of logical file?

Ans:

 Logical file

 

·         Logical file does not occupy any memory.

·         One or more logical file can be derived from a single physical file.

·         It simply contains the record selection definition and when accessed retrieves the records from the physical file to which it refers.

·         A logical file can contain up to 32 record formats.

·         It selects records dynamically. It cannot exist without a physical file.

·         We can filter the data with criteria by using select and omit command.

·          A logical file does not contain any data but provides the ‘VIEWS’ of the data to satisfy end-user’s needs.

 

Ü  Types of Logical file

 There are two types:

1)      Non-join logical file

2)      Join logical file

 

 

1)     Non-join logical file

Non-join logical files can either be a simple logical file, which contains only one record format or a multiple record format logical file, which contains more than one Record format.

Logical files can be derived from 1 to 32 physical files and so a logical file can have a maximum of 32 record formats.

 

ü  Single record format Non-join logical file:

If a logical file is derived from single physical file it is called simple logical file.

 


Columns . . . :    1  71           Browse                        AMINEM/DDSSRC 
SEU==>                                                               MULTIFRMT 
FMT LF .....A..........T.Name++++++.Len++TDpB......Functions++++++++++++++++++        
       *************** Beginning of data *************************************
0002.00      A          R ACCOUNT                   PFILE(AMINEM/ACCOUNT)      
0003.00      A          K ACCOUNTNUM                                               
0005.00      A          K ACCURRENCY

 

 

ü  Multiple record format Non-join logical file:

·         Multiple record non-join logical files will select records from 2 or more physical files by referring to only one logical file.

·         Each record format is always associated with one or more physical file.

·         The same PF can be used in more than one record format.

 


Columns . . . :    1  71           Browse                         AMINEM/DDSSRC
SEU==>                                                               MULTIFRMT
FMT LF .....A..........T.Name++++++.Len++TDpB......Functions++++++++++++++++++
*************** Beginning of data *************************************
0002.00      A          R ACCOUNT                   PFILE(AMINEM/ACCOUNT)
0003.00      A          K ACCOUNTNUM
0005.00      A          K ACCURRENCY
0006.00      A          R TRANS                     PFILE(AMINEM/TRANS)
0007.00      A          K TACCOUNT
0008.00      A          K TCURRENCY
****************** End of data ****************************************

 

 

2. What is DYNSLT?

Ans:

     DYNSLT: Use this file-level keyword to indicate that the selection and omission tests specified in the file (using select/omit specifications) are done at processing time. This keyword specifies dynamic select/omit rather than access path select/omit.

    Only a Physical file contains data. Logical files just contain pointers for processing the data in a specific sequence and/or subset of data.     
When a record is added/changed/deleted in a physical file, the system has to put a lock on it and then go out to check and update any logical files before it can release the lock. While the amount of time to do this is hardly measurable, it can be significant if massive batch updates are done to a file.            
If you are using the Select/Omit option in your DDS and using DYNSLT, the above process does not need to be done at record update time.         
Where this is beneficial is when your selection process includes almost all the records in the file. Now when you process using DYNSLT, it will read all the records in the file, but do the selection of which records to process at that time rather than having done all the maintenance ahead of time.

 

3. What is the Difference between access path and Dynamic select?

Ans: Dynamic select occurs whenever the program reads file. But access path occurs before the file is read (but  not necessarily).

 

4. What is the use of JDUPSEQ in AS400?

Ans:

JDUPSEQ

This join–level keyword is used to specify the order in which records with duplicate join fields are presented when the JLF is read.

 

The format for this keyword is:

JDUPSEQ (Sequencing field-name [*DESCEND])

                  

ü  This keyword has no effect on the ordering of records with unique keys.       

ü  If *DESCEND is not specified then the default is sequencing in ascending order.

Example:  JDUPSEQ (Sequencing Duplicate Objects)

 


Columns . . . 1 71            Edit                     AMINEM/EXAMPLE
 SEU==>                                                         SEQ1
 FMT PF.
        *************** Beginning of data ***********************
0001.00                 R SEQREC1
0002.00                   EMPNO          5P 0
0003.00                   EMPNAME1      20A
0004.00                   ADDRESS       20A
0005.00                 K EMPNO
        ****************** End of data **************************

 

         EMPNO   EMPNAME1              ADDRESS
 000001 10,001   BOB                   23,OLD MADIWALA
 000002 10,002   DANNY                 50,LONG ISLAND
 000003 10,003   PRINC                 90,ATTUR
 ****** ******** End of report  ********

 

 

 


Columns . . . 1 71            Edit                     AMINEM/EXAMPLE
 SEU==>                                                         SEQ2
 FMT PF
        *************** Beginning of data****************
0001.00                 R SEQREC2
0002.00                   EMPNO          5P 0
0003.00                   EMPNAME       20A
0004.00                   TEL           10P 0
        ****************** End of data ******************


   EMPNO   EMPNAME                         TEL
 000001 10,001   BOB                         825,777
 000002 10,001   BOB                         825,999
 000003 10,001   BOB                         825,888
 000004 10,002   DANNY                     4,222,600
 ****** ******** End of report  ********
 

 

 


Columns . . . 1 71            Edit                     AMINEM/EXAMPLE
 SEU==>                                                   JDFTSEQ
 FMT LF
        *************** Beginning of data ******************
0001.00                 R RECSEQ                    JFILE (SEQ1 SEQ2)
0002.00                 J                           JOIN (1 2)
0003.00                                             JFLD (EMPNAME1 EMPNAME)
0004.00                                             JDUPSEQ (TEL)
0005.00                   EMPNO                     JREF (2)
0006.00                   EMPNAME1
0007.00                   ADDRESS
0008.00                   TEL
        ****************** End of data************************

 

        EMPNO   EMPNAME1              ADDRESS                         TEL
 000001 10,001   BOB                   23,OLD MADIWALA             825,777
 000002 10,001   BOB                   23,OLD MADIWALA             825,888
 000003 10,001   BOB                   23,OLD MADIWALA             825,999
 000004 10,002   DANNY                 50,LONG ISLAND            4,222,600
 ****** ******** End of report  ********

 

 

5. What is the use of JDFTVAL in AS400?

Ans:

JDFTVAL

·         When this file-level keyword is used the system provides default values for all for fields when a join to a secondary file does not produce any records.

·         If this keyword is not specified a record in the primary file for which there is no corresponding record in the secondary file is skipped.

 





 

 







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