Systems Design - Overview
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
- description of field
- source of data
- data type
- comments about layout
Types of reports include:
Types of screens include:
- external forms to be sent outside company (bills, invoices etc.)
- menus to show options
- screens that gather data
- screens that display retrieved data
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:
- 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).
- 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
- 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)
- Information over the phone or in person can be keyed into a screen program that edits
the data and interactively requests changes and corrections
- Character reading such as standardized test forms
- Misc. data entry devices.
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:
Documentation for the file:
- Database system being used and how the file fits into the database.
- Non-database system, file structure.
- Storage media - disk etc.
- Organization of the file: sequential, indexed, relative, relational database
- Access to the file: sequential, random, dynamic
- Backup procedures
- Set-up including blocking factors, fixed or variable length records etc.
- Make choices based on file accessibility, file activity, file capacity, file processing speed, file costs
- Determine the fields that are needed, the type of data in each field, whether it is to be packed, display or binary
- layout form
- record format analysis form including field, description, type, length, source and
comments (If this information is included in a data dictionary then you just need to list
fields and possible source and comments)
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).
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.
- Manual Procedures
- Maintenance - updating
- Output that needs to be generated
- File retention
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:
- Verify that all data has been processed
- Block or trap data with errors from entry into processing
- Be able to reconstruct information if computer files are destroyed
- Prohibit tampering with information by unauthorized individuals
- Prevent employee fraud
- Provide an audit trail
Four major types of controls:
- Source document controls
- Matching counts an/or amounts on source documents to controls and amounts entered into
- Batch-balance totals or for transaction processing a transaction-batch total
- Input controls
- Account/user # and password
- Checking data transmission via journal - recorded transmissions can be used for error
checking and recovery
- Check point printing
- Control access to certain files and certain fields
- Program controls
- Edit and update programs
- Mixed mode, limit/range, reasonableness, presence or absence of data, special checks
like check digits, matching re3cords and verification on second field, field relationships
- Control reports
- Verify that control totals balance
- Verify that record is correctly processed through the system
- Batch processing
- Test records and transactions to follow processing through the system
- Maintain file balance procedures
- Store beginning and ending balances of record counts and amounts
- Keep track of additions, changes, deletions, errors and their effects
- Output controls
- Special output controls on documents (numbered checks, orders, special forms etc.)
- Regulating access
- Balance printing at end of documents to indicate number printed, amounts etc.
(helps provide audit trail)
- Control of exception or errors
- Sampling of data