Data flow diagrams represent the logical flow of data within the system. DFD uses few symbols like circles and rectangles connected by arrows to represent data flows. DFD can easily illustrate relationships among data, flows, and external entities stores. DFD can also be drawn in increasing levels of detail, starting with a summary high level view and proceeding to more detailed lower level views.. The open-ended boxes represent data stores, sometimes called files or databases. These data stores correspond to all instances of a single entity in a data model. Arrow represents data flows, inputs and outputs to end from the processes. A number of guideline should be used in DFD Choose meaningful names for the symbols on the diagram.
Number the processes consistently. The numbers do not imply the sequence. Avoid over complex DFD.
Make sure the diagrams are balanced Data Dictionary
The data dictionary is used to create and store definitions of data, location, format for storage and other characteristics. The data dictionary can be used to retrieve the definition of data that has already been used in an application. The difficulty to determine a correct and complete set of information is on account of the factors given below: The capability constraint of the human being as an information processor, a problem solver and a decision-maker. The nature and the variety of information in precise terms. Reluctance of decision-makers to spell out the information for the political and the behavioral reasons. The ability of the decision-makers to specify the information. In spite of these difficulties, methods are evolved based on the uncertainty scale, starting from the low to the high level of uncertainty. There are four methods of determining the information requirements. They are: Asking or interviewing
Determining from the existing system
Analyzing the critical success factors
Experimentation and modeling.
Asking or Interviewing
In this method a designer of the MIS puts questions or converses with the user of the information and determines the information requirements. When the user has to select one answer from a finite set of answers a closed question should be asked. For example, "Which are the raw materials used for making a product? “But an open question is put, when the user has no precise knowledge but has an ability to determine all answers to select one out of them? For example, "Which are the raw materials which can be used in a product?" In open questions, the answers may not be immediate but can be obtained by surveying the domain knowledge of the user. When multiple users or several decision-makers in similar functions or positions are involved, a brain storming session is performed to cover all possible answers to the questions. The experts or experienced users are asked to give their best answers - this approach is called the Delphi method. In all these methods, the system designer has to test the validity of all the answers independently.
Determining from the Existing System
In a number of cases the existing system, which has been evolved after a number of years, and has been designed out of experience gives straightaway the requirement of information. In any situations, systems from other companies can give additional information requirements. The fund of knowledge is available from the textbooks, handbooks, research studies which can determine the information requirement. For example, systems such as the accounts receivables, the accounts payables, the pay roll, the inventory control, the financial accounting, etc., have a well determined, information requirement. Irrespective of the type of organization and business, ninety percent of the information requirement is common and the balance ten per cent may be typical to...