MELJUN CORTES Data Flow Diagram


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MELJUN CORTES Data Flow Diagram

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  • This phase is divided into two subphases: preliminary design , in which the analyst establishes the new system concept, followed by detailed design , in which the analyst determines exact design specifications. The reason this phase is divided into two parts is that an analyst wants to make sure management approves the overall plan before spending time on details.
  • At this stage it is wise to make a formal presentation of the plan or the alternatives. The point is that you do not want to commit time and energy to - nor does the user wants to pay for - a detailed design until you and the user agree on the basic design.
  • MELJUN CORTES Data Flow Diagram

    1. 1. Systems Modeling MELJUN CORTESMELJUN CORTES
    2. 2. System Model A representation of an in-place or proposed system that describes the data flow throughout the structure. The model describes the points where data or information enters a system and places where it will be processed, as well as the actions taken and the points where data will be output.
    3. 3. A system model is documented through a variety of DESIGN DIAGRAM a graphic or visual representation of a structure. It includes data flow diagrams, structured charts, decision trees, and other items.
    4. 4. Advantages of a Design Diagram • Serves as a communications tool. It provides a concrete, visual medium for describing complex plans or problem solution • Serves as a planning tool. It helps the SA to visualize the relationships and movements that will exist within a system while it is still in the planning stages • Provide an overview of a system. Makes it possible to see the important elements and relationships in a system , free of extraneous details - birds-eye view of the major steps and processes.
    5. 5. Advantages of a Design Diagram • Define roles. It spells out in pictorial forms the roles played by personnel and workstations and processes in a system where it shows data, forms and reports generated and the end results produced. • Demonstrate relationships. Points out relationships that may not be readily obvious from verbal or written descriptions. It shows how data elements relate to each other, as well as the relationships between parts of a system.
    6. 6. Advantages of a Design Diagram • Promote logical procedures. It helps SA clarify and refine their thinking and to describe explicitly all paths, branches and flows in a system. With this, SA can identify incorrect branches and missing elements and may discover more efficient way to implement a part of a system. • Facilitate troubleshooting. It serves as a blue print of the inner working of a system, to which the troubleshooter can refer when diagnosing a system failure.
    7. 7. Advantages of a Design Diagram • Document a system. It records graphically, clearly, and permanently the important elements of a system. This facilitates making changes, revisions, and modifications at a later date. It also enables those unfamiliar with a system to grasp its elements easily and quickly.
    8. 8. System Design the evaluation of alternative solutions and the specification of a detailed computer- based solution this phase includes resolving any user design issues and developing the technical, detailed design of each specific program
    9. 9. System Design review system requirements, then to consider some of the major aspects of a system. Preliminary Design “Should the system be centralized or distributed?” “Should the system be on-line?” “Should packaged software be purchased as opposed to having programmers write new software?” “Can the system be run on the user’s personal computer?” “How will input data be captured?” “What kind of reports will be needed?”
    10. 10. Modeling Tools
    11. 11. Data Flow Diagram a graphic illustration that shows the flow of data and logic within a system. the shape of the symbol indicates to the analyst that a specific operation is performed. The arrows that connect the symbol shows the different direction in which the data flows.
    12. 12. Data Flow Diagram The detail and complexity of data flow diagram varies with the system being described. As you work As you work with the systems, you will find yourself continually relying upon diagrams such as these to shows points where data originates, is processed or transformed, and is output.
    13. 13. Four Basic Symbols External Entity a square box that specifies either the source or the destination of data. It shows where data originates outside a system or where it will be transmitted after processing, always outside the system. • sometimes called sources and sinks. Source - a point outside the system that generates data Sink - a point outside the system that receives data • both are external entities, drawn as square boxes
    14. 14. Four Basic Symbols Process drawn as a rectangle with rounded corners. It represents the transformation or processing of information within a system. The process symbols shows those places in a system where calculations are made or where information is changed in character. 1.5 The top of the process box is usually ruled off, leaving space to enter a reference number. The reference number is used to key more detailed data flow diagrams to the box
    15. 15. Four Basic Symbols Data Store a point in a system where information is permanently or temporary stored or held. It shown as a rectangle with one end open. The left side of the box may be ruled off to enter a reference number, which keys the box to other diagrams 1.7 data may be stored on filing cards, ledger sheets, floppy disk or even on the check stubs in a checkbook. While stored, the information remains intact and is not changed or modified in any way.
    16. 16. Four Basic Symbols Flowline sometimes called pipes or vectors, connect external entities, process, and data store elements. Information flow may be one-way or two-way. One or two arrows are drawn between boxes to show which way the information flows these lines, always drawn with a arrowhead, trace the flow of information throughout the system.
    17. 17. How To Draw Data Flow Diagrams
    18. 18. How to draw data flow diagrams 1. Do not mix levels of detail on one chart. Instead, draw several data flow diagrams, each with a different level of detail. 2. Select either the Gane and Sarson or Yourdon* notations and use them consistently. *Yourdon uses a circle for a process, while Gane and Sarson uses a rectangle with rounded corners. Yourdon’s data store symbol is a rectangle open at each end. Gane and Sarson show a data store as a rectangle closed at one end.
    19. 19. How to draw data flow diagrams 3. Use a template to draw uniformly sized and shaped symbols for permanent system documentation. Symbols may be drawn freehand for rough or temporary diagrams. 4. Connect symbols with flowlines. Draw connections using pipes or lines with arrowheads to show the flow of data between symbols. Place an arrowhead at each end of the pipe to show a two-way flow of data between symbols. Place an arrowhead at one end of the pipe to show a one-way flow of data.
    20. 20. How to draw data flow diagrams 5. Name and label all symbols and connectors. Select names that are descriptive and reflect what is being done. Place text within each symbol describing the function or transformation taking place. Place textual labels next to flowlines or pipes to describe the movement or transformation of data taking place. 6. Correlate symbols to other data flow diagrams, using reference numbers to show relationships
    21. 21. How to draw data flow diagrams 7. Desk check all data flow diagrams to make sure each symbols is logically connected to another 8. Connect symbols with flowlines. Draw connections using pipes or lines with arrowheads to show the flow of data between symbols. Place an arrowhead at each end of the pipe to show a two-way flow of data between symbols. Place an arrowhead at one end of the pipe to show a one-way flow of data.
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