Skip to main content
UploadLanguage (EN)Support
BusinessMobileSocial MediaMarketingTechnologyArt & PhotosCareerDesignEducationPresentations & Public SpeakingGovernment & NonprofitHealthcareInternetLawLeadership & ManagementAutomotiveEngineeringSoftwareRecruiting & HRRetailSalesServicesScienceSmall Business & EntrepreneurshipFoodEnvironmentEconomy & FinanceData & AnalyticsInvestor RelationsSportsSpiritualNews & PoliticsTravelSelf ImprovementReal EstateEntertainment & HumorHealth & MedicineDevices & HardwareLifestyle
NK
Uploaded byNeha Kaurav
PPTX, PDF4,849 views

DFD ppt

The document discusses data flow diagrams (DFDs). It explains that DFDs are graphical tools used to represent the flow of data through a system. They show external entities, processes, data stores, and data flows. DFDs provide an overview of what data a system processes, what transformations are performed, what data is stored, and what results are produced. They are useful for structured analysis and communicating requirements to users and managers. The document then describes the key elements of a DFD and provides guidelines on their construction and use.

Downloaded 120 times
NEHA KAURAV CLASS: BCA 3rd SEM.
 A graphical tool, useful for communicating with users, managers, and other personnel.  Used to perform structured analysis to determine logical requirements.  Useful for analyzing existing as well as proposed systems.  Focus on the movement of data between external entities and processes, and between processes and data stores.  A relatively simple technique to learn and use.
• Provides an overview of- – What data a system processes – What transformations are performed – What data are stored – What results are produced and where they flow • Graphical nature makes it a good communication tool between- – User and analyst – Analyst and System designer
• Source/Sinks (External entities) • Data flows • Processes • Data Stores
• A Rectangle represents an external entity • They either supply or receive data • They do not process data External Entities Source – Entity that supplies data to the system. Sink – Entity that receives data from the system.
• Data in motion • Marks movement of data through the system - a pipeline to carry data. • Connects the processes, external entities and data stores. – Generally unidirectional, If same data flows in both directions, double-headed arrow can be used. Data Flow
• A circle represents a process • Straight line with incoming arrows are input data flows • Straight lines with outgoing arrows are output data flows • Labels are assigned to Data flow. These aid documentation 1. STORES Stores demand note Delivery Slip Issue Slip
• A Data Store is a repository of data • Data can be written into the data store. This is depicted by an incoming arrow • Data can be read from a data store. This is depicted by an outgoing arrow • External entity cannot read or write to the data store • Two data stores cannot be connected by a data flow Data StoresD1 Data StoresD1 Data StoresD1 Writing Reading
• Data can flow from – External entity to process – Process to external entity – Process to store and back – Process to process • Data cannot flow from – External entity to external entity – External entity to store – Store to external entity – Store to store
• Use meaningful names for data flows, processes and data stores. • Use top down development starting from context diagram and successively levelling DFD • Only previously stored data can be read • A process can only transfer input to output. It cannot create new data • Data stores cannot create new data
 Context diagram  Level-0 diagram (System diagram)  Level-n diagram - Detail of one process from next highest level  Primitive diagram (Lowest level DFD)
 If a process p is expanded, the process at the next level are labelled as p.1, p.2 etc.  All data flow entering or leaving p must also enter or leave it’s expanded version  Expanded DFD may have data stores  No external entity can appear in expanded DFD  Keep the number of processes at each level less than 7
 Draw one process representing the entire system (process 0)  Find all inputs and outputs that come from or go to external entities; draw as data flows.  Draw in external entities as the source or destination of the data flows.
Context Diagram External entity Data flow The entire system
IT’S A BAD DFD  Do not use direct data flows from one data store to another. There must be a process between the store.s  Do not use direct data flows from an external entity to a data store flows. Again, a process is needed between them.  Do not show direct data flows between external entities.
Bad! Flow between external entities Weather bureauFire brigade Weather forecast Call for help Assess fire risk Weather forecast
Bad! Flow direct to data store Weather bureauFire brigade Weather forecast Call for help Assess fire risk Weather forecast Forecast history
Bad! Flow direct between data stores Customer Stock numbers Process order Invoice Orders Inventory Stock check Order Order
DFD ppt