Zohaib Dfd


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Data Flow Diagram

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Zohaib Dfd

  1. 1. Zohaib Siddique<br />presents <br />Data Flow Diagram<br />
  2. 2. What is it?<br />A model that indicates the flow of data through a system.<br />Represented using Data Flow Diagrams(DFD)<br />
  3. 3. Data Flow Diagrams are:<br />Used to perform structured analysis to determine logical requirements<br />A graphical tool, useful for communicating with users, managers, and other IS personnel<br />Useful for analyzing existing as well as proposed systems<br />A relatively simple technique to learn and use<br />
  4. 4. Purposes of DFDs<br />Unexploded DFDs are useful to identify information requirements<br />Exploded DFDs can be used for<br />presentation<br />education<br />gathering feedback information from users<br />
  5. 5. It is the first step towards implementation<br />It helps guide the development of user interfaces<br />Guides the user through choices and avoids meaningless steps<br />Good way to verify requirements with your client.<br />Advantages of DFD<br />
  6. 6. Uses of DFDs<br />Used to analyze the system to ensure that the design is complete <br />Used to partition the system into programs<br />Used for system documentation<br />
  7. 7. Data Flows<br />data in motion<br />marks movement of data through the system - a pipeline to carry data<br />connects the processes, external entities and data stores<br />Unidirectional<br />originate OR end at a process (or both)<br />name as specifically as possible - reflect the composition of the data - a noun<br />do not show control flow! Control flow is easy to identify- a signal with only one byte - (on/off). <br />HINT: if you can&apos;t name it: either it&apos;s control flow, doesn&apos;t exist or you need to get more information!<br />
  8. 8. Processes<br />transform incoming data flows into outgoing data flows<br />represent with a bubble or rounded square <br />name with a strong VERB/OBJECT combination; examples:<br />create_exception_report <br />validate_input_characters <br />calculate_discount<br />process<br />
  9. 9. Data Stores<br />data at rest<br />represents holding areas for collection of data, processes add or retrieve data from these stores<br />name using a noun (do not use ‘file’)<br />only processes are connected to data stores<br />show net flow of data between data store and process. For instance, when access a DBMS, show only the result flow, not the request<br />data store<br />
  10. 10. Different Types of DFDs<br />Context diagram <br />Level-0 diagram (system diagram) <br />Level-n diagram <br />Primitive diagram<br />
  11. 11. Context Diagram<br />defines the scope of the system by identifying the system boundary<br />contains: <br />one process (which represents the entire system)<br />all sources/sinks (external entities)<br />data flows linking the process to the sources and sinks (external entities)<br />
  12. 12. Level-0 Diagram<br />describes the overall processing of the system<br />show one process for each major processing step or functional requirement<br />data flows from the context appear on system diagram also (level balancing)<br />can show a single data store to represent all data in aggregate at this level<br />can draw duplicate sources, sinks and data stores to increase legibility<br />
  13. 13. Drawing a Level-0 Diagram<br />list the major data stores<br />list major business steps<br />draw a segment for each business step<br />assemble into single DFD<br />re-organize until satisfied<br />number processes<br />
  14. 14. Functional Decomposition<br />similar to a series of more detailed maps<br />iterative process of breaking the description of a system into finer and finer detail to create a set of charts in which one process on a given chart is explained in greater detail on another chart<br />referred to as exploding, partitioning, or leveling<br />must use your judgment to decide what goes on each level<br />show error and exception handling on lower levels (if at all)<br />
  15. 15. Quality Guidelines<br />Completeness<br />all components included & in project dictionary<br />Consistency<br />between levels: balancing, leveling<br />Timing considerations<br />assume system never starts and never stops<br />Iterative nature<br />revisions are common<br />Drawing primitives (lowest level)<br />when to stop?<br />
  16. 16. Users command & data Display info.<br /> Alarm type<br /> Sensor status <br /> Telephone no. tones <br />Level 0<br />Control pannel display<br />Control Pannel<br />Safe Home Software<br />Alarm<br />Sensors<br />Telephone line<br />
  17. 17. Level 1<br />User commands &<br />dataConfigure requestConfiguration information<br />Stop <br />StartConfig dataConfig . Information<br /> A/d msg <br />passwordDisplay info.<br />Valid ID msg<br />Sensor info<br />Alarm type<br />Sensor status<br />Telephone no.tones<br />Control pannel<br />Configure info<br />Activate/Deactivate<br /> system<br />Interact with user<br />Display msg &<br /> status<br />Control pannel <br />display<br />Process password<br />Alarm<br />Monitor system<br />Sensors<br />Telephone line<br />
  18. 18. Level 2<br />Sensor information<br />Alarm type<br />Sensor information Alarm Data<br /> Sensor ID, type<br />Telephone number<br /> Telephone number tones<br /> Sensor status<br />Access <br />against setup<br />Generate alsrm <br />signal<br />Access aiainst <br />setup<br />Read sensors<br />Dial Phone<br />
  19. 19. And that’s the end.<br />
  20. 20. INVITATION<br />Yours existance will highly be appreciated on 16th August 2009 at 10:00PM in my wedding ceremony at Sheraton Hotel, Karachi.<br />Invitation Cards will be handed to you soon.<br />