SAD-System Design

System Design is a solution. It tells the approach to the creation of a new system. It provides the methods to implement the system given in the feasibility study. Emphasis is placed on transforming the performance requirements to design specifications. Design is done both logically and physically.


The design phase focuses on the detailed implementation of the system recommended in the feasibility study. The design phase is a transition from a user-oriented document to a document oriented to the programmers or data base personnel.

System design goes through two phases of development
  • Logical design
  • Physical design
Logical design:

The logical system design specifies the user needs at a level of detail that determines the required information flow into and out of the system and the required data resources. The design covers the following:

1. Reviews the current physical system-its data flow, file content, volumes, frequencies, etc.
2. Prepares output specifications-determines the format, content, and frequency of reports, including terminal specifications and locations.
3. Prepares input specifications-format, content, and most of the input functions.  This includes determining the flow of the document from the input data source  to the actual input location.
4. Prepares edit, security and control specifications.
5. Specifies the implementation plan.
6. Prepares a logical design of the information flow, output, input, controls and  implementation plan.
7. Reviews benefits, costs, target dates and system constraints.

Physical design:

This produces the working system by defining the design specifications that tell programmers exactly what the candidate system must do. In turn programmers write the necessary programs or modifies the software package that accepts input from the user. It performs the necessary calculations on the existing file or data base, produces the report on a hardcopy or displays it on a screen, and maintains an updated data base at all times.

Physical system design consists of the following steps.

1.Design the physical system.

a. Specify input/output media.
b. Design the database and specify backup procedures.
c. Design physical information flow through the system and a physical design walkthrough.

2.Plan system implementation

a. Prepare conversion schedule and a target date.
b. Determine training procedure, courses, and timetable.

3.Devise a test and implementation plan and specify any new hardware /software 

4.Update benefits, costs, conversion date, and system constraints.
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