August 1999
SD206 : SYSTEMS DESIGN

QUESTION 3

Total Marks: 20 Marks

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(a) Describe each of the following type of file:

(i) History file.

(ii) Transaction file.

(iii) Security file.

(iv) Work file.

  

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(i) A history file is a copy which is created and saved for archiving ; new history files do not replace old ones: both are saved.

(ii) A transaction file is a temporary file, which is usually considered to be finished with when the data is transferred to the master file.

(iii) A security file exists for backup purposes, which must be created periodically to replace outdated copies.

(iv) A work file is a temporary file used for a single task; some work files contain copies of master file records, while others contain copies of transaction file records.

 
(b) (i) What are access controls?

(ii) List three access controls which might be considered during the design of a system.

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(i) Access controls are means of limiting access of data to authorised personnel only.

(ii)

  • Unique transaction codes.
  • Use of non-display fields.
  • Restricted functions.
  • Separation of duties.

 
(c) (i) Describe two types of file controls which are direct concern to a systems analyst.

(ii) Describe two effective methods for maintaining backup copies of files.

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(i)
  • Include a grand total as the last record of the master file. As new records are developed, the totals of transactions are accumulated; if the beginning grand total plus the accumulated transaction total is equal to the new grand total, processing may continue.
  • Identify all fields necessary to reconstruct the current versions of critical files. Typically, this will be concerned with files necessary to satisfy business, legal and regulatory requirements.

 
(ii)
  • Master file dumps. This involves duplicating the master file to create another copy of it; if the current copy becomes damaged or erased, the transactions accumulated since the last dump can be applied to the backup copy.
  • Record image copies. This involves keeping before and after images of the master file, which can provide enough information to reconstruct records if they are damaged or lost.