1. Programming Logic and Design Fourth Edition, Comprehensive
Chapter 11
Sequential File Merging, Matching,
and Updating

2. Objectives Understand sequential files and the need for merging them
Create the mainline and housekeeping() logic for a merge program
Create the mergefiles() and finishUp() modules for a merge program
Modify the housekeeping() module to check for eof
Programming Logic and Design, Fourth Edition, Comprehensive

3. Objectives (continued)
Understand master and transaction file processing
Match files to update master file fields
Allow multiple transactions for a single master file record
Update records in sequential files
Programming Logic and Design, Fourth Edition, Comprehensive

4. Understanding Sequential Data Files and the Need for Merging Files
Sequential file: records are stored one after another in some order
Temporal order: order based on time
Records are often stored based on the contents of one or more fields within each record
Merging files: combining two or more files while maintaining the sequential order
Programming Logic and Design, Fourth Edition, Comprehensive

5. Understanding Sequential Data Files and the Need for Merging Files (continued)
Two conditions required for merging files:
Each file must have same record layout
Each file must be sorted in the same order based on the same field
Programming Logic and Design, Fourth Edition, Comprehensive

6. Understanding Sequential Data Files and the Need for Merging Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

7. Creating the Mainline and housekeeping() Logic for a Merge Program
Mainline logic similar to other file processing programs, except for handling two files
With two input files, must determine when both files are at eof
In housekeeping() module:
Define a flag variable to indicate that both files have reached eof
Must define two input files
At end of module, read one record from each input file
Programming Logic and Design, Fourth Edition, Comprehensive

8. Creating the Mainline and housekeeping() Logic for a Merge Program (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

9. Creating the Mainline and housekeeping() Logic for a Merge Program (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

10. Creating the mergeFiles() and finishUp() Modules for a Merge Program
Two records are in memory, one from each file
Must decide which record to write to output file first
After writing one record, must read again from the same file
Then compare both records again to determine which is written next
Must always have one record from each file to compare before writing one
Programming Logic and Design, Fourth Edition, Comprehensive

11. Creating the mergeFiles() and finishUp() Modules for a Merge Program (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

12. Creating the mergeFiles() and finishUp() Modules for a Merge Program (continued)
Merge technique:
Compare two records
Write the record with the lower value
Read another record from the same input file
Programming Logic and Design, Fourth Edition, Comprehensive

13. Creating the mergeFiles() and finishUp() Modules for a Merge Program (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

14. Creating the mergeFiles() and finishUp() Modules for a Merge Program (continued)
Data to be merged:
Programming Logic and Design, Fourth Edition, Comprehensive

15. Creating the mergeFiles() and finishUp() Modules for a Merge Program (continued)
High value: a value that is greater than any possible value in a field
Because the files are different lengths, you must continue to process the longer file
To use the same loop, you must handle the comparison operation
Technique:
Use a high value for the comparison to guarantee that the record will be “selected” and written
Programming Logic and Design, Fourth Edition, Comprehensive

16. Creating the mergeFiles() and finishUp() Modules for a Merge Program (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

17. Creating the mergeFiles() and finishUp() Modules for a Merge Program (continued)
When both files are at eof, execute the finishUp() module
Programming Logic and Design, Fourth Edition, Comprehensive

18. Modifying the housekeeping() Module in the Merge Program to Check for eof
Must check for eof during first read, in case one file is empty
Programming Logic and Design, Fourth Edition, Comprehensive

19. Modifying the housekeeping() Module in the Merge Program to Check for eof (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

20. Modifying the housekeeping() Module in the Merge Program to Check for eof (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

21. Master and Transaction File Processing
When merging files, the records usually contain the same fields in the same order
When not the same format, one file may be used to update another file
Master file: holds relatively permanent data
Transaction file: contains temporary data to be used to update the master file
Matching record: record in the master file with same key field value as a record in the transaction file
Programming Logic and Design, Fourth Edition, Comprehensive

22. Master and Transaction File Processing (continued)
Matching may be done for several reasons:
To update the master file: transaction file record is used to make changes to the master file record
Use information from both master and transaction file to create another entity, such as an invoice
There may be 0, 1, or many transaction records matching each master file record
Two approaches to updating a master file:
Update in place, changing the existing master file
Create a copy of the master, making the changes in the new version
Programming Logic and Design, Fourth Edition, Comprehensive

23. Master and Transaction File Processing (continued)
When a new copy of the master is created during updating:
Parent file: original saved master file
Child file: updated version of master file
Programming Logic and Design, Fourth Edition, Comprehensive

24. Matching Files to Update Fields in Master File Records
Logic used to match records in two files is similar to merge logic
Programming Logic and Design, Fourth Edition, Comprehensive

25. Matching Files to Update Fields in Master File Records (continued)
Goal: create a new master file with updated custTotalSales field
Technique:
Inspect each master file record
Determine if there are any new transaction records matching the master file record
Add transaction amount to master file custTotalSales field in master record
Pre-sorting both master and transaction files will improve the efficiency
Programming Logic and Design, Fourth Edition, Comprehensive

26. Matching Files to Update Fields in Master File Records (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

27. Matching Files to Update Fields in Master File Records (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

28. Matching Files to Update Fields in Master File Records (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

29. Matching Files to Update Fields in Master File Records (continued)
3 possibilities when comparing records:
transCustNumber value = custNumber
transCustNumber value > custNumber
transCustNumber value < custNumber
If =, update custTotalSales
If >, there was no sale for that customer
If <, there is no matching master record  error
Programming Logic and Design, Fourth Edition, Comprehensive

30. Matching Files to Update Fields in Master File Records (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

31. Matching Files to Update Fields in Master File Records (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

32. Allowing Multiple Transactions for a Single Master File Record
To handle multiple transactions for a single master file record, you must
Match a transaction to the master file record
Process that transaction
Read again only from the transaction file
Determine if the new transaction applies to the same master record
Programming Logic and Design, Fourth Edition, Comprehensive

33. Allowing Multiple Transactions for a Single Master File Record (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

34. Updating Records in Sequential Files
Application must be able to:
Make changes to data in a master file record
Add new records to master file
Eliminate records in master file
Transaction file records usually contain a transaction code to indicate the type of action to take
Programming Logic and Design, Fourth Edition, Comprehensive

35. Updating Records in Sequential Files (continued)
Types of transaction records:
Addition: create a new master file record
Deletion: remove a master file record
Change: modify data in a master file record
Programming Logic and Design, Fourth Edition, Comprehensive

36. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

37. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

38. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

39. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

40. Updating Records in Sequential Files (continued)
When transaction record matches master file record:
If transaction code = “A”  error
If transaction code = “C”, make the changes in the master record
If transaction code is not “A” or “C”, must be a “D”, so do not write existing master file record to the new master file
When complete, read one new record from each of the input files
Programming Logic and Design, Fourth Edition, Comprehensive

41. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

42. Updating Records in Sequential Files (continued)
If master file record > transaction record, there is no master file record that matches the transaction record
If transaction code is not an “A”  error
When complete, do not read another master record
There may be more transactions for the newly added record
Programming Logic and Design, Fourth Edition, Comprehensive

43. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

44. Updating Records in Sequential Files (continued)
If master file record < transaction record, there is no transaction record that matches the transaction record
Write the master file record to the new master file
Read the next master file record
Programming Logic and Design, Fourth Edition, Comprehensive

45. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

46. Updating Records in Sequential Files (continued)
If transaction file reaches eof first, set transEmpNum to 999
Master file record will always be lower, causing master file record to be written to new master file
If master file reaches eof first, set EmpNum to 999
Transaction record will always be lower, causing new records to be added (if code = “A”) or error to be generated (if code not = “A”)
When both files reach eof, set bothAtEof = “Y” and perform finishUp() module
Programming Logic and Design, Fourth Edition, Comprehensive

47. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

48. Updating Records in Sequential Files (continued)
Programming Logic and Design, Fourth Edition, Comprehensive

49. Summary
Sequential file: records are stored one after another in some order
Key field: field on which you sort records
When merging two files
Compare records from each input file
Write the appropriate record from one file
Read another record from the same file
When eof is reached on one input file, set key field to a high value and finish processing the other file
Programming Logic and Design, Fourth Edition, Comprehensive

50. Summary (continued) Master file: holds relatively permanent data
Transaction file: holds temporary data that corresponds to records in master file
To match transaction file and master file, determine if a transaction record exists for each master
If yes: update or delete the master based on the transaction code
If no: add a new master record based on the transaction code
Programming Logic and Design, Fourth Edition, Comprehensive

51. Summary (continued) With multiple transactions per master file record
Process a matching transaction record
Read again from the transaction file
When transaction record > master file record, read from master file
Transaction file records usually have the same fields as the master, with a transaction code field
Programming Logic and Design, Fourth Edition, Comprehensive