System design is the process of defining the architecture, components, modules, interfaces, and data for a system to satisfy specified requirements. Systems design could be seen as the application of systems theory to product development.
Types of DFD : DFDs are of two types: Physical DFD and Logical DFD.
Physical DFD :
Logical DFD :
A system has the following properties −
For example, in an organization, purchasing department must interact with production department and payroll with personnel department.
System Documentation : System documentation serves as the technical specifications for the IS and how the objectives of the IS are accomplished. Users, managers and IS owners need never reference system documentation. System documentation provides the basis for understanding the technical aspects of the IS when modifications are made.
Major Activities in requirement Determination :
Requirements Anticipation :
Requirements Investigation :
Requirements Specifications :
Types of Files used in an Organization System
Master file − It contains the current information for a system. For example, customer file, student file, telephone directory.
Table file − It is a type of master file that changes infrequently and stored in a tabular format. For example, storing Zipcode.
Transaction file − It contains the day-to-day information generated from business activities. It is used to update or process the master file. For example, Addresses of the employees.
Temporary file − It is created and used whenever needed by a system.
Mirror file − They are the exact duplicates of other files. Help minimize the risk of downtime in cases when the original becomes unusable. They must be modified each time the original file is changed.
Log files − They contain copies of master and transaction records in order to chronicle any changes that are made to the master file. It facilitates auditing and provides mechanism for recovery in case of system failure.
Archive files − Backup files that contain historical versions of other files.
Feasibility Study : Feasibility Study can be considered as preliminary investigation that helps the management to take decision about whether study of system should be feasible for development or not.
Steps Involved in Feasibility Analysis :
The following steps are to be followed while performing feasibility analysis
Program Documentation :
Operations Documentation : Operations documentation contains all the information needed for processing and distributing online and printed output. Operations documentation should be clear, concise, and available online if possible.
It includes the following information −
Secondary Research or Background Reading : This method is widely used for information gathering by accessing the gleaned information. It includes any previously gathered information used by the marketer from any internal or external source.
Questionnaires : This method is used by analyst to gather information about various issues of system from large number of persons.
There are two types of questionnaires :
Open-ended Questionnaires − It consists of questions that can be easily and correctly interpreted. They can explore a problem and lead to a specific direction of answer.
Closed-ended Questionnaires − It consists of questions that are used when the systems analyst effectively lists all possible responses, which are mutually exclusive.
Advantages of questionnaires :
Systems Models :
Schematic Models :
Flow System Models :
Static System Models :
Dynamic System Models : Business organizations are dynamic systems. A dynamic model approximates the type of organization or application that analysts deal with. It shows an ongoing, constantly changing status of the system. It consists of −
Types of Systems :
Physical or Abstract Systems : Physical systems are tangible entities. We can touch and feel them.
Physical System may be static or dynamic in nature. For example, desks and chairs are the physical parts of computer center which are static. A programmed computer is a dynamic system in which programs, data, and applications can change according to the user's needs.
Abstract systems are non-physical entities or conceptual that may be formulas, representation or model of a real system.
Open or Closed Systems : An open system must interact with its environment. It receives inputs from and delivers outputs to the outside of the system. For example, an information system which must adapt to the changing environmental conditions.
A closed system does not interact with its environment. It is isolated from environmental influences. A completely closed system is rare in reality.
Adaptive and Non Adaptive System : Adaptive System responds to the change in the environment in a way to improve their performance and to survive. For example, human beings, animals.
Non Adaptive System is the system which does not respond to the environment. For example, machines.
Permanent or Temporary System : Permanent System persists for long time. For example, business policies.
Temporary System is made for specified time and after that they are demolished. For example, A DJ system is set up for a program and it is dissembled after the program.
Natural and Manufactured System : Natural systems are created by the nature. For example, Solar system, seasonal system.
Manufactured System is the man-made system. For example, Rockets, dams, trains.
Deterministic or Probabilistic System : Deterministic system operates in a predictable manner and the interaction between system components is known with certainty. For example, two molecules of hydrogen and one molecule of oxygen makes water.
Probabilistic System shows uncertain behavior. The exact output is not known. For example, Weather forecasting, mail delivery.
Social, Human-Machine, Machine System : Social System is made up of people. For example, social clubs, societies.
In Human-Machine System, both human and machines are involved to perform a particular task. For example, Computer programming.
Machine System is where human interference is neglected. All the tasks are performed by the machine. For example, an autonomous robot.
Man–Made Information Systems : It is an interconnected set of information resources to manage data for particular organization, under Direct Management Control (DMC).
This system includes hardware, software, communication, data, and application for producing information according to the need of an organization.
Man-made information systems are divided into three types −
Interviewing : Systems analyst collects information from individuals or groups by interviewing. The analyst can be formal, legalistic, play politics, or be informal; as the success of an interview depends on the skill of analyst as interviewer.
It can be done in two ways
Advantages of Interviewing :
A system must have three basic constraints −
For example, traffic management system, payroll system, automatic library system, human resources information system.
User Documentation : It includes instructions and information to the users who will interact with the system. For example, user manuals, help guides, and tutorials. User documentation is valuable in training users and for reference purpose. It must be clear, understandable, and readily accessible to users at all levels.
The users, system owners, analysts, and programmers, all put combined efforts to develop a user’s guide.
A user documentation should include:
System design takes the following inputs :
System design gives the following outputs :
It is a process of collecting and interpreting facts, identifying the problems, and decomposition of a system into its components.
System analysis is conducted for the purpose of studying a system or its parts in order to identify its objectives. It is a problem solving technique that improves the system and ensures that all the components of the system work efficiently to accomplish their purpose.
The objective of system must be central. It may be real or stated. It is not uncommon for an organization to state an objective and operate to achieve another.
The users must know the main objective of a computer application early in the analysis for a successful design and conversion.
Structured Analysis is a development method that allows the analyst to understand the system and its activities in a logical way.
It is a systematic approach, which uses graphical tools that analyze and refine the objectives of an existing system and develop a new system specification which can be easily understandable by user.
It has following attributes :
Documentation Control :
Documentation is a process of recording the information for any reference or operational purpose. It helps users, managers, and IT staff, who require it. It is important that prepared document must be updated on regular basis to trace the progress of the system easily.
After the implementation of system if the system is working improperly, then documentation helps the administrator to understand the flow of data in the system to correct the flaws and get the system working.
Programmers or systems analysts usually create program and system documentation. Systems analysts usually are responsible for preparing documentation to help users learn the system. In large companies, a technical support team that includes technical writers might assist in the preparation of user documentation and training materials.
Types of Feasibilities :
Economic Feasibility :
Operational Feasibility :
Behavioral Feasibility :
Schedule Feasibility :
The word System is derived from Greek word Systema, which means an organized relationship between any set of components to achieve some common cause or objective.
A system is “an orderly grouping of interdependent components linked together according to a plan to achieve a specific goal.”
Structured Analysis Tools : During Structured Analysis, various tools and techniques are used for system development. They are −
Joint Application Development (JAD) : It is a new technique developed by IBM which brings owners, users, analysts, designers, and builders to define and design the system using organized and intensive workshops. JAD trained analyst act as facilitator for workshop who has some specialized skills.
Advantages of JAD
A requirement is a vital feature of a new system which may include processing or capturing of data, controlling the activities of business, producing information and supporting the management.
Requirements determination involves studying the existing system and gathering details to find out what are the requirements, how it works, and where improvements should be made.
File Organization : It describes how records are stored within a file.There are four file organization methods.
It comes to System Design, there are following four main documentations :
Review of Records, Procedures, and Forms : Review of existing records, procedures, and forms helps to seek insight into a system which describes the current system capabilities, its operations, or activities.