Data Flow Diagram - DFD Levels, Symbols, Case Study, Tutorial, Example,

The Analysis Model is the first technical representation of a system. Analysis Modeling uses a combination of text and diagrams to represent software requirements (data, function, and behavior) in an understandable way. Building analysis models helps make it easier to uncover requirement inconsistencies and omissions. Two types of analysis modeling are commonly used:  (1) Structured Analysis (2) Object-Oriented Analysis Data Modeling uses Entity-Relationship Diagrams to define data objects, attributes, and relationships. Functional Modeling uses Data Flow Diagrams (DFD)   to show how data are transformed inside the system. Behavioral Modeling uses State Transition Diagrams to show the impact of events. Analysis work products must be reviewed for completeness, correctness, and consistency . Work Products of Analysis Modeling: Data object descriptions Entity relationship diagrams Data flow diagrams State transition diagrams Process specifica...

1.       Explain the relationship and differences between a module and a program. A program is a set of modules that work together to perform all the required functions. A module is a relatively small set of statements that carry out a single function.  2.       What is the purpose of the automation system boundary? How do you develop one? The automation system boundary defines which processes are going to be automated within the computer system, and which processes are part of the environment, or manual system. The system boundary, although needed for both structured and object-oriented development, needs to be defined explicitly for the structured approach. The object-oriented approach already has the system boundary defined in the use case diagram.  The automation system boundary is developed at the DFD fragment level or below, by defining which processes are manual and which are aut...

A data flow diagram, like other models, has limitations. It is important to be aware of these limitations. Otherwise, it is easy to misunderstand data flow diagrams by making invalid inferences or by trying to read into a data flow diagram meaning which were not intended. (1) A data flow diagram does not show flow of control.   It is not a flowchart.   When alternative outputs may result from decisions within a transformation; a data flow diagram shows only the alternative outputs, not the decisions.  Only the incoming data flows appear as inputs to a transformation; if events or stimuli other than these inputs are necessary to activate the transformation, they are not shown. A transformation may be carried out many times while the system is in operation, but it is shown only once. A data flow diagram does not show details linking inputs and outputs within a transformation. It shows only all possible inputs and outputs for each...

     A Data Flow Diagram is a network model of an information processing system. The arcs of the network represent data flows, and the nodes represent data stores, transforms, or selected elements of the environment. A Data Flow is a movement of information within the system or across the system boundary. A data flow which crosses the system boundary to enter the system is called a net system input  or simply System Input .  A data flow which crosses the boundary to leave the system is called a net system output or System Output . A Data Store is a time-delayed repository of information, where data is kept temporarily or permanently, avoid thinking of them in computer "file" terms, there are many quite different forms. A Process , or Transform , is a transformation that inputs one type of data and outputs a different type. It is a conversion of data from one form to another. A process cannot output data without ge...

A data dictionary is a catalog- a repository of the elements in a system. The major elements are data flows, data stores and processes. For example suppose you want to print the vendor’s name and address at the bottom of a cheque the data dictionary might define vendor’s name and address as follows Why Data dictionary is important ? ·          Analysts use data dictionaries for five important reasons : 1.    To manage the detail in large systems 2.    To communicate a common meaning for all system elements 3.    To document the features of the system 4.    To facilitate analysis of the details in order to evaluate characteristics and determine where system changes should be made. 5.    To locate errors and omissions in the system.

An implementation dependent view of the current system, showing what task are carried out and how they are performed. Physical characteristics include -       Names of people -       Forms and document Name -       Names of department -       Master and transaction files -       Equipments and devices used -       Locations Most comprehensive and useful approach to developing an accurate and complete description of current system begins with the development of a physical DFD. The use of physical DFD is desirable for 3 reasons Firstly it is easier to describe the interaction between physical components then it is to understand the policies that are used to manage the applications. Secondly physical DFD are useful for communication with users. User’s relate easily to peop...

(1)         Simplicity of Notation makes user to understand the process being studied and hence users can make suggestion for modification to more accurately understand and describe business activity. Avoiding mistakes at early stages helps in preventing system failure. (2)         It permits analyst to isolate areas of interest in the organization and study them by examining the data that enter the process and seeing how they are changed when they leave. (3)         A comprehensive system investigations produces set of many data flow diagrams some providing overview and other’s going into detail to show data elements, data stores and processing steps for specific components of a larger system.

(1)         Data Flow Diagram : A graphic tool used to describe and analyze the movement of data through the system- manual or automated including the processes, data stores and delays in the system. (2)         Data Dictionary : The logical characteristics of current systems data stores, including name, description, aliases, contents, and organization. (3)         Data Structure Diagram : A pictorial description of the relation between entities (people, places, events and things) in a system and the set of information about the entity. (4)         Structure Chart : A design tool that pictorially shows the relation between processing modules in computer software.

·          What processes make up the system? ·          What data are used in each process? ·          What data are stored? ·          What data enter and leave the system? ·          Entire emphasis is on the data analysis as can be seen from the previous question. ·          Following the flow of data through business processes tells analyst a great deal about how organization objectives are accomplished. ·            In the course of handling transactions and completing task data are input, processed, stored, retrieved, used, changed and output. ·          Data Flow Analysis studies the use of data in each activity. ·        ...

Structured Analysis is a development method for analysis of existing manual or automated systems, leading to the development of a specification for a new modified system. The underlying objective in structured analysis is to organize the task associated with requirements determination to provide an complete understanding of a current situation. The word “structure” in structured analysis means 1.     The method attempts to structure the requirements determination process beginning with the documentation of existing system. 2.     The process is organized in such a way that it attempts to include all relevant detail that describe the current system. 3.     It is easy to verify when relevant details have been omitted. 4.     The identification of requirements will be similar among individual analyst and will include best solution and strategies for systems development. 5.     ...