Chapter 13 Sequential File Processing Master Files Set

Chapter 13 Sequential File Processing

Master Files • Set of files used to store companies data in areas like payroll, inventory • Usually processed by batch processing • Typically stored on magnetic disk – Disks can store billions of characters – Disk drives read, write data quickly – Disk records can be any size

Sequential Files • Records always read in sequence • Read first record, process it, then read second record, process it and so on – Payroll records in order by employee number may be processed in sequence for updating or printing reports

Sequential Files • 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.

Master File Procedures Typical procedures for sequential processing in batch mode are: • Designing Master File • Creating Transaction File • Updating Master File • Reporting from Master File

Designing a Master File • 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 • Group common fields together (i. e. , address)

Designing a Master File • Choose field size large enough to accommodate data stored in it • Use coded fields where possible to save space • Be sure all date fields include four-digit year

Creating a Master File • 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

Creating a Transaction File • Changes to master file made with separate procedure • Change records stored in file called transaction file

Updating a Master File • Updating is process of making master file current • Update master file by incorporating changes from transaction records

Reporting from a Master File • 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

Creating Master, Transaction Files • 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

Sequential File Updating 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

Sequential File Updating 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

Ordering of Records • 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

Master/Transaction Processing • Records in both files must be sorted (sequenced) on the same key • Records from each file are “matched”