Systems Design - Overview

Designing Output:

The most common output is screen or printer output. Other types of output such as plotters, audio response, multimedia etc. need to be considered. Instead of printers, reports can be put on computer output microfilm (COM), on disk, sent as a FAX, put on the Web etc.
Documentation of output consists of layout form (printer layout, screen layout etc.) and a report analysis form that gives basic information such as:
Detail lines and summary total lines should both be explained when detailing the layout of the report/screen.
Types of reports include:
Types of screens include:

Designing input:

Input data is decided on based upon the output that is required. You must have the input to produce the output. The analyst must decide how to have the data available to the computer. Some data is keyed in directly, some data is keyed in a code form and the translation of that code is either on a table file, in a memory table, or translated using IF etc. Data should only be collected for the system once. If it is needed in more that one application than it should be accessible from storage.

Analyst must consider both data gathering and data entry into the system. Data entry can be done either by data entry clerks where speed and accuracy are important and knowledge of the data is not or by clerks involved in the actual application of the data who can make corrections to the data as they enter/process it.

Data can be gathered by:
  1. Clerks filling out forms with information (the inventory clerk fills out a form for a new product to be carried or the payroll clerk fills out a form on a new employee).
  2. By completed turnaround documents (the oil man is given a document that tells the identification number, name and address to deliver to and they add the amount of the delivery.
  3. Using forms that have been filled in by others and entering the data from them (add/drop forms are filled out by a student and turned in to the registrar)
  4. Information over the phone or in person can be keyed into a screen program that edits the data and interactively requests changes and corrections
  5. Character reading such as standardized test forms
  6. Scanning
  7. Misc. data entry devices.
Input Documentation:

If a form or screen is used, the form/screen and the instructions to fill it out should be part of the documentation.

There should be a layout of the computer readable input record accompanied by a input documentation form that shows the field, description, data type, number of characters, source and appropriate comments.

Design of Files:

When designing files, you must determine the following:
  1. Database system being used and how the file fits into the database.
  2. Non-database system, file structure.
  3. Storage media - disk etc.
  4. Organization of the file: sequential, indexed, relative, relational database
  5. Access to the file: sequential, random, dynamic
  6. Backup procedures
  7. Set-up including blocking factors, fixed or variable length records etc.
  8. Make choices based on file accessibility, file activity, file capacity, file processing speed, file costs
  9. Determine the fields that are needed, the type of data in each field, whether it is to be packed, display or binary
  10. Controls
  11. Security
Documentation for the file:

Design of Processing:

Flow of data through the system is analyzed using the data flow diagrams from the analysis state. These diagrams are now refined and completed and possibly a systems flowchart is draw showing the flow of data (files and processing).

Processing considerations:
In processing, we determine what manual operations need to be done to prepare the data and deal with the results of the processing. We determine the order of processing that must be accomplished. We determine what programs must be written and develop program specifications to enable to programming staff to write the programs. Logic tools can be used to show the logic that must be dealt with in certain procedures/programs. The programmer will receive the necessary input, output, file descriptions and layouts and the program specifications complete with logic descriptions where necessary as well as the controls that must be included.

Documentation includes a write-up of the whole system accompanied by data flow diagrams and/or systems flowcharts as well as the input, output and file documentation developed and the program descriptions and any accompanying logic definitions.

Controls: The purpose of controls is to:
  1. Verify that all data has been processed
  2. Block or trap data with errors from entry into processing
  3. Be able to reconstruct information if computer files are destroyed
  4. Prohibit tampering with information by unauthorized individuals
  5. Prevent employee fraud
  6. Provide an audit trail

Four major types of controls: