1. 13- 1 Chapter 13

2.  Overview of Sequential File Processing  Sequential File Updating - Creating a New Master File  Validity Checking in Update Procedures  Update Procedures with Multiple Transaction Records 13- 2

3.  Balanced Line Algorithm for Sequential File Updating  Sequential File Updating - Rewriting Records on Disk  Matching Files for Checking Purposes  Interactive Updating of Sequential File 13- 3

4.  Records always read in sequence  Read first record, process it, then read second record, process it and so on ◦ For example payroll records in order by employee number may be processed in sequence for updating or printing reports 13- 4

5.  May be sorted into any sequence using any field in record ◦ To distribute checks more easily, records may be sorted by department  Sequential processing then used to print checks, reading first record, then second, etc. 13- 5

6.  Set of files used to store companies data in areas like payroll, inventory  Usually processed by batch processing  Need updated on a regular basis 13- 6

7. Typical procedures for sequential processing in batch mode are:  Designing Master File  Creating Master File  Creating Transaction File  Updating Master File  Reporting from Master File 13- 7

8.  Place key fields that uniquely identify record at beginning of record  If possible, choose numeric key fields  Secondary fields after primary key fields  Remaining fields appear in order of importance 13- 8

9.  Choose field size large enough to accommodate data that may be stored in it  Use coded fields where possible to save space (not a big problem anymore)  Be sure all date fields include four-digit year 13- 9

10.  Original master file data entered interactively, stored on disk file  Ensure data integrity by using data validation techniques to minimize risk or errors  Control listing or audit trail produced to show data stored in new master file and control totals 13- 10

11.  Changes to master file made with separate procedure  Changed records stored in file called transaction file 13- 11

12.  Create a new blank file (New Master)  Updating is process of making master file current  Update master file by incorporating changes from transaction records 13- 12

13.  Scheduled reports prepared on regular basis from data stored in master file ◦ Sales reports, customer bills, checks, etc. ◦ Use detail, exception and group printing techniques  On demand reports produced as need arises ◦ May be in report form or displayed on screen 13- 13

14.  Data may be read in from another file or entered interactively from keyboard  If data entered is valid, move it to master or transaction record fields  WRITE new record to file 13- 14

15. Two input files  Input Master File (Old-Master) ◦ Current through previous updating period ◦ Does not contain changes since previous update  Input Transaction File (Trans-File) ◦ Contains changes since previous update to be applied to Old-Master 13- 15

16. Two output files  Output Master File (New-Master) ◦ Integrates data from Old-Master with all of changes from Trans-File ◦ Will become Old-Master for next update  Control Listing or Audit Trail ◦ Print file showing changes made to master file, errors during processing and control totals 13- 16

17.  Records in Old-Master and Trans-File must be in order by same key field  Compare key fields to determine if given master record is to be updated 13- 17

18.  For accounts receivable file, account number may be selected as key field  Records in both input files in sequence by account number ◦ Old-Master key field is M-Acct-No ◦ Trans-file key field is T-Acct-No  New-Master file also created in account number sequence (Acct-No-Out) 13- 18

19.  One transaction record for each master record to be updated (p. 570) ◦ Contains total amount to be added to amount field in corresponding master record  Initially, record read from both Old-Master and Trans-File  Comparison of M-Acct-No and T-Acct-No determines next step 13- 19

20.  Means transaction record exists with same account number as master record  Perform regular update, adding Trans-File amount to Old-Master amount, storing result in New-Master field  Write record to New-Master file  Read next record from both Old-Master and Trans-File 13- 20

21.  Means master record exists for which there is no corresponding transaction record  Write record from Old-Master to New-Master as is, since no changes need to be made to it  Read next record from Old-Master  Basically do nothing but copy  The most likely thing to happen 13- 21

22.  Means transaction record exists for which there is no corresponding master record  Two ways to process this transaction ◦ Create record in New-Master file for this transaction (maybe a new client?) ◦ May assume that T-Acct-No is invalid since no match found in Old-Master file and treat as error condition (depends on how the accounting works) 13- 22

23.  COBOL reserved word HIGH-VALUES  Move it into a variable (p. 573)  Refers to largest value in computer's collating sequence  Used so all records from both Old-Master and Trans-File are processed  So the program keeps transferring the old trans data to the new trans data  May reach end of Old-Master file before reaching end of Trans-File or vice versa 13- 23

24.  When last record read from Old-Master, M- Acct-No set to HIGH-VALUES ◦ For all remaining transaction records ◦ T-Acct-No < M-Acct-No ◦ Processed as new accounts and added to New- Master ◦ This allows the transaction file to keep going when you are out of files from the old master file 13- 24

25.  When last record read from Trans-File, T- Acct-No set to HIGH-VALUES ◦ For all remaining Old-Master records T-Acct- No > M-Acct-No ◦ Old-Master records added to New-Master without changes ◦ Old keeps going 13- 25

26.  Loop to process records ends only when both account numbers equal HIGH-VALUES  May be used only with fields defined as alphanumeric ◦ Define account number fields with PIC of Xs even though fields contain numbers 13- 26

27.  Code field may be added to each transaction record to indicate whether transaction is ◦ New account to be added ◦ Update to existing account ◦ Deletion of existing account  Comparison of keys and transaction code type enable program to detect other update errors 13- 27

28.  To process more than one change for each master record requires different update procedure  In accounts receivable file example, transaction record may be created for each purchase or credit by customer  Amounts in all transaction records for one customer need to be added to amount in Old-Master file record 13- 28

29.  Add loop to regular update routine to read and process multiple transaction records for same Old-Master record ◦ Continue to read records from Trans-File until T-Acct-No Not = M-Acct-No 13- 29

30.  Technique to update master file ◦ With any number of transactions ◦ With checks for error conditions  Viewed as most efficient and effective sequential file updating method  Two new fields used to control updating ◦ WS-Control-Key ◦ WS-Allocated-Switch 13- 30

31.  Determines type of processing  Called control or active key field  Set to smaller of M-Acct-No or T-Acct-No  Then comparison of M-Acct-No or T-Acct- No to WS-Control-Key used to control further processing  Kind of like the control break processing 13- 31

32.  Used for error control ◦ To ensure records processed correctly ◦ To detect erroneous codes in transactions  Set to 'YES' when record should be written to New-Master file  Set to 'NO' if record should not be written to New-Master file 13- 32

33.  WS-Control-Key set to M-Acct-No  WS-Allocated-Switch set to 'YES' because WS-Control-Key and M-Acct-No are same  Since M-Acct-No and T-Acct-No not equal, Old-Master has no transactions ◦ Old-Master record written to New-Master record as is 13- 33

34.  WS-Control-Key set to M-Acct-No  WS-Allocated-Switch set to 'YES' because WS-Control-Key and M-Acct-No are same  Transactions with T-Acct-No = M-Acct-No processed 13- 34

35.  Processing transactions with T-Acct-No = M-Acct-No ◦ Updates posted to New-Master ◦ Additions displayed as errors because WS- Allocated-Switch set to 'YES' (master record with this M-Acct-No already exists) ◦ Deletions move 'NO' to WS-Allocated-Switch to ensure this Old-Master record is not written to New-Master file 13- 35

36.  WS-Control-Key set to T-Acct-No  WS-Allocated-Switch set to 'NO' because WS- Control-Key not equal to M-Acct-No ◦ No master record exists for this transaction 13- 36

37.  Only additions acceptable ◦ Reset WS-ALLOCATED-SWITCH to 'YES' ◦ New-Master record created from transaction record  Update or deletion transaction treated as error  Full example p. 588-590 13- 37

38.  May read a master disk record, make changes directly to same record, and rewrite it or update it in place  Only two files needed ◦ Master-FileOPEN as I-O ◦ Trans-FileOPEN as INPUT  Use REWRITE statement to replace master disk record, currently in storage, that was accessed by preceding READ 13- 38

39.  To delete a record, establish each record with an activity code field ◦ For example, Code-X = 1 if record is active, or 2 if record is inactive ◦ Probably want this code anyway for various bookkeeping reasons  All master records initially active (1 in Code-X)  Master record deactivated by changing activity code to 2, not actually deleting it. 13- 39

40.  New records cannot be added in sequence when file open for I-O  Can add records at end of file by opening file in EXTEND mode OPEN EXTEND file-name  Disk automatically positioned at end of file, immediately after last record  Sort file after records added to arrange them in sequence  Issues here, you need to close then open and records are added unsorted 13- 40

41.  Sequential updating by creating new master uses three files ◦ Incoming master file ◦ Transaction file with change records ◦ New output master file that will incorporate all changes 13- 41

42.  Sequential updating technique ◦ All three files must be in sequence by same key field ◦ Record read from each file ◦ Routine performed depends on whether key fields match 13- 42

43.  Sequential updating technique ◦ Transaction record may include coded field to designate update, deletion, addition ◦ Use HIGH-VALUES to ensure all records in both old master and transaction files are processed  Balanced line algorithm used for sequential updates 13- 43

44.  Can also update records in sequential file by rewriting them in place ◦ Must open file as I-O  Records can be added to end of sequential file ◦ Open in EXTEND mode 13- 44