Zohaib Dfd
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The document describes data flow diagrams (DFDs), including what they are, their purposes and uses, and the different types of DFDs. DFDs show the flow of data through a system and are used to model systems for requirements analysis, design, documentation and more. They contain processes, data stores, external entities and data flows. The different types of DFDs include context diagrams, level-0 diagrams, and more detailed lower-level diagrams.
Zohaib Dfd
- 1. Zohaib Siddiquepresents Data Flow Diagram
- 2. What is it?A model that indicates the flow of data through a system.Represented using Data Flow Diagrams(DFD)
- 3. Data Flow Diagrams are:Used to perform structured analysis to determine logical requirementsA graphical tool, useful for communicating with users, managers, and other IS personnelUseful for analyzing existing as well as proposed systemsA relatively simple technique to learn and use
- 4. Purposes of DFDsUnexploded DFDs are useful to identify information requirementsExploded DFDs can be used forpresentationeducationgathering feedback information from users
- 5. It is the first step towards implementationIt helps guide the development of user interfacesGuides the user through choices and avoids meaningless stepsGood way to verify requirements with your client.Advantages of DFD
- 6. Uses of DFDsUsed to analyze the system to ensure that the design is complete Used to partition the system into programsUsed for system documentation
- 7. Data Flowsdata in motionmarks movement of data through the system - a pipeline to carry dataconnects the processes, external entities and data storesUnidirectionaloriginate OR end at a process (or both)name as specifically as possible - reflect the composition of the data - a noundo not show control flow! Control flow is easy to identify- a signal with only one byte - (on/off). HINT: if you can't name it: either it's control flow, doesn't exist or you need to get more information!
- 8. Processestransform incoming data flows into outgoing data flowsrepresent with a bubble or rounded square name with a strong VERB/OBJECT combination; examples:create_exception_report validate_input_characters calculate_discountprocess
- 9. Data Storesdata at restrepresents holding areas for collection of data, processes add or retrieve data from these storesname using a noun (do not use ‘file’)only processes are connected to data storesshow net flow of data between data store and process. For instance, when access a DBMS, show only the result flow, not the requestdata store
- 10. Different Types of DFDsContext diagram Level-0 diagram (system diagram) Level-n diagram Primitive diagram
- 11. Context Diagramdefines the scope of the system by identifying the system boundarycontains: one process (which represents the entire system)all sources/sinks (external entities)data flows linking the process to the sources and sinks (external entities)
- 12. Level-0 Diagramdescribes the overall processing of the systemshow one process for each major processing step or functional requirementdata flows from the context appear on system diagram also (level balancing)can show a single data store to represent all data in aggregate at this levelcan draw duplicate sources, sinks and data stores to increase legibility
- 13. Drawing a Level-0 Diagramlist the major data storeslist major business stepsdraw a segment for each business stepassemble into single DFDre-organize until satisfiednumber processes
- 14. Functional Decompositionsimilar to a series of more detailed mapsiterative 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 chartreferred to as exploding, partitioning, or levelingmust use your judgment to decide what goes on each levelshow error and exception handling on lower levels (if at all)
- 15. Quality GuidelinesCompletenessall components included & in project dictionaryConsistencybetween levels: balancing, levelingTiming considerationsassume system never starts and never stopsIterative naturerevisions are commonDrawing primitives (lowest level)when to stop?
- 16. Users command & data Display info. Alarm type Sensor status Telephone no. tones Level 0Control pannel displayControl PannelSafe Home SoftwareAlarmSensorsTelephone line
- 17. Level 1User commands &dataConfigure requestConfiguration informationStop StartConfig dataConfig . Information A/d msg passwordDisplay info.Valid ID msgSensor infoAlarm typeSensor statusTelephone no.tonesControl pannelConfigure infoActivate/Deactivate systemInteract with userDisplay msg & statusControl pannel displayProcess passwordAlarmMonitor systemSensorsTelephone line
- 18. Level 2Sensor informationAlarm typeSensor information Alarm Data Sensor ID, typeTelephone number Telephone number tones Sensor statusAccess against setupGenerate alsrm signalAccess aiainst setupRead sensorsDial Phone
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