Data Flow DiagramsElements of a DFDData FlowsProcessesSlide 5Data StoresExternal EntityDFD LevelsContext DiagramLevel - 0Level-nPhysical vs LogicalDFD RulesData Store/Entity RulesData Flow RulesMore Data Flow RulesDeliverables for Process ModelingData Flow DiagramsA picture of the movement of data between external entities and the processes and data stores within a systemElements of a DFD•Data Flows•Processes•Data Stores•External EntitiesData Flows•Shows data in motion•Data moves from one plan in a system to another•Denoted by a line with an arrowhead, indicating the flow•Must have a label to explain what data is flowingProcesses•The work or actions (including decisions) performed on the data so that they are transformed, stored or distributed•Includes –process number generally in the upper left hand corner– the person performing the process in the upper right hand corner–a description of the process is in the main boxProcesses•Data flows into and out of a processes into an external entity or data store•Indicated by an oval in DeMarco and Yourdon format and by a “rounded” rectangle in the Gane and Sarson formatData Stores•Data at rest–may take the form of many different physical representations•Denoted by an open rectangle•Labeled–M for manual data stores•File folders, filing cabinets, index cards–D for computer data•Data filesExternal Entity•Also called source/sink•The sources of destinations of data OUTSIDE the system•Denoted by a closed rectangle or an eclipse•Include a description of the entity in the box•Can repeat an entity on the diagram–Avoid crossing lines–Indicate a repeated entity by a diagonal line through a corner of the entityDFD Levels•Context level–Overview only–Labeled by 0•Decompose into more detailed levels–Level 0•Processes are numbered 1.0, 2.0, 3.0…–Level 1 or Detailed Level•Processes are numbered 1.1, 1.2, 1.3...Context DiagramAn overview of an organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between the entities and the systemLevel - 0•The first decomposition of the context diagram–Decomposition - an iterative process of breaking the description of a system down into finer and finer detail which creates a set of charts in which one process on a given chart is explained in greated detail on another chart•A data flow diagram that represents a systems major processes, data flows and data stores at a high level of detailLevel-nA DFD that is the result of n nested decompositions of a series of sub-processes from a process on a level-0 diagramPhysical vs Logical•Physical shows more details–Includes person doing the work •what they do•Logical View–Remove the “physical” processes from the physical DFD–Reduce the DFD to its basic functionsDFD Rules•Processes–No process can have only outputs–No process can have only inputs–Every process must have a labelData Store/Entity Rules•Data cannot move directly from one data store to another data store–Must be processed•Data cannot move directly from an entity to a data store or from a data store to an entity–Must be processedData Flow Rules•A data flow has only one direction of flow between symbols. The data can flow in both directions (as in an update routine)–Generally shown by two data flows–One flowing from the data store to the process–One flowing from the process to the data store•Can flow from one process to another, but cannot flow directly back to original processMore Data Flow Rules•A data flow to a data store implies a file update•A data flow from a data store implies data retrievalDeliverables for Process Modeling•DFD of physical system •DFD of logical system - Level 0•Optional: A decomposition of one function•Thorough descriptions of each DFD component Oracle Designer will automatically create the Context Level Diagram from the level 0