Logical and Physical Design of an Information System

Logical Design of an IS You develop the logical design of an information system during the systems analysis phase. The logical design defines the functions and features of the system and the relationship among its components. The logical design includes the output that must be produced by the system, the input needed by the system, and the process that must be produced by the system without regard to how tasks will be accomplished physically.

Logical Design of an IS a logical design defines what must take place, not how it is to be accomplished. logical designs do not address the actual methods of implementation.

Example: The Logical Design of a Customer Record System describes the data that must be entered for each customer specifies that records must be displayed in customer number order, and explains what information to produce for a customer status report Specifications for the actual input, or entry, of data, the sorting method, the physical process of creating the report, and the exact format of the report are not part of the logical design.

Physical Design of an IS the physical design of an information system is a plan for the actual implementation of the system. you develop the physical design during the systems design phase. the physical design is built on the system’s logical design and describes a specific implementation, much like a working blue print describes the actual construction of a building.

Physical Design of an IS the physical design describes the actual processes of entering, verifying, and storing data; the physical layout of data files; the sorting procedures; the exact format of reports; and so on. Whereas logical design is concerned with what the system must accomplish, physical design is concerned with how the system will meet those requirements.

The relationship of Logical and Physical design good system design is impossible without careful, accurate system analysis. the design phase typically cannot begin until the analysis work is complete. It is better to complete the analysis phase before moving on to systems design.

SYSTEMS ANALYSIS GUIDELINES

Three (3) main activities of system analysis phase: STEP ACTIVITY DESCRIPTION 1 Requirements modeling Involves fact-finding to describe the current system and identification of the requirement s for the new system, such as outputs, inputs, processes, performance, and security. 2 Data and process modeling A graphically modeling process to represent system data and process using traditional structured analysis techniques. Structured analysis identifies the data flowing into a process, the business rules that transform the data, and the resulting output data flow.

Development strategies STEP ACTIVITY DESCRIPTION 3 Development strategies In development strategies, you will consider various options and prepare for the transition to the systems design phase. The deliverable, or end product, of the system analysis phase is a system requirement document, which is an overall design for the new system

SYSTEMS DESIGN GUIDELINES

Three (3) main activities of system design phase: STEP ACTIVITY DESCRIPTION 1 Review system requirements Become familiar with the logical design. 2 Design the system User interface Design an overall user interface, including screens, commands, controls, and features that enable users to interact with the application. Input processes Determine how data will be input to the system and design necessary source documents.

STEP ACTIVITY DESCRIPTION Input and output Design the physical layout for each input and output formats and reports screen and printed reports. Data Determine how data will be organized, stored, maintained, updated, accessed, and used. System Architecture Determine processing strategies and methods, client/server interaction, network configuration, and internet/intranet interface issues.

Present the system design STEP ACTIVITY DESCRIPTION 3 Present the system design Create the system design specification document, in which you describe the proposed system design, the anticipated benefits of the system, and the estimated development and implementation costs.

SYSTEM DESIGN CONSIDERATIONS User Consideration Data Consideration Architecture Consideration Consider points where users interact with the system Anticipate future user, system, and organizational needs Enter data where and when it occurs Verify data where it is input Use automated data entry methods whenever possible Control access for data entry Report every instances of entry and change of data Enter data only once Use a modular design Design independent modules that perform a single function

Logical System Design (System Analysis Phase) Data Flow Diagrams Data Dictionary Process Descriptions Physical System Design (System Design Phase) Entity-Relationship Diagram Normalization of Database User Interface and Reports