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What are Data FlowDiagrams? A data flow diagram (DFD) is a graphical representation of the "flow" of data through an information system. A data flow diagram can also be used for the visualization of data processing (structured design). It is common practice for a designer to draw a context-level DFD first which shows the interaction between the system and outside entities. This context-level DFD is then "exploded" to show more detail of the system being modeled
Data Flow Diagram Symbols There are only four symbols: › Squares representing external entities, which are sources or destinations of data. › Rounded rectangles representing processes, which take data as input, do something to it, and output it. › Arrows representing the data flows, which can either be electronic data or physical items. › Open-ended rectangles representing data stores, including electronic stores such as databases or XML files and physical stores such as or filing cabinets or stacks of paper.
Data Flow Diagram Symbols Process Actions performed on data so that they are transformed, stored or distributed. This can be a computerised Or manual transformation Data Flow E.g. Result of a query to a database, contents of a printed report : data that moves together to common destinations
Data Flow Diagram Symbols Data Store A physical location to hold data e.g. A file folder or notebook etc. Source Origin and/or destination of the data. Often referred to as external entities as they are outside the system. We are only interested in how data flows in to or from the system to
Contd.. Data flow diagrams can be used to provide a clear representation of any business function. The technique starts with an overall picture of the business and continues by analyzing each of the functional areas of interest. This analysis can be carried out to precisely the level of detail required.
Common Modeling Rules All processes must have at least one data flow in and one data flow out. All processes should modify the incoming data, producing new forms of outgoing data. Each data store must be involved with at least one data flow. Each external entity must be involved with at least one data flow. A data flow must be attached to at least one process.
Context or Level 0 Diagram The highest level view of a system. This only has one process which represents the overall function of the system and has no data stores as all the data is stored within the process. Now we demonstrate the Level 0 or Context Diagram for Multiplex Management System.
Multiplex ManagementSystem Now we see the Data Flow or Level 1 diagram of the Multiplex Management System
Box office file Level 1DFD Smoke/CO detectors Smoke alarm Message Store Emergency Services Alert CO alarm Message Alert Action Repor Proces t s Details Changes Feedbac Send Supply Unit Owner Report k Invoke Weekly Process Collection Reel Status In/Out Staff Dispatch Stock order Supplier Mainten ance Movie List Cleaning/UpgradesOrder/Supply Food stall Send details Screens Booking Book Seats Availability Box OfficeOnline Booking Confirmation Collection Proces Invoice Issue bill Tickets/ s Coupon Collection Booking Request Tickets s Transactio Book Ticket n Product ticket/coupons Debit/credit card/ Cash Customer
Advantages to Using DFD Data flows and process consequences. ◦ Wherever we start in the process, we can understand the processing steps that the needed to take to complete the relevant transaction(s) and to inform its constituents of the results. Data inputs and outputs. ◦ The DFD also makes it possible to understand what data are needed to provide appropriate inputs to any processing step.
Contd.. Simplifying complexity by isolating process components. ◦ The DFD would make it easier to capture the detail of such data flows. ◦ At the time that DFDs were developed, this shift towards modularizing data flows and processing elements represented a major step forward in enabling systems analysts to add useful structure to process representations rapidly and easily.
Data Dictionary A data dictionary is an integral part of a database, which holds information about the database and the data that it stores, i.e., the meta- data. A data dictionary is a simple yet effective add-on to ensure data consistency. All the information required to create the data dictionary must be identified and recorded in the design documents
Data Dictionary Customer Details: Customer Name = First Name + (Middle Initial) + Last Name Payment=Method of payment +(Credit Card type * Credit Card Number * Expiration Date) Customer Number = (Residence|Mobile|Office) *Integer string length upto 10*
Data Dictionary Ticket Details: Movie_name= *character length upto 20* Screen= digit *1 digit number less than 10* Ticket_info= Movie_name + (Date * Time) Class= Char *char string length upto 10* Seat_no= char + digit + digit *1 character and 2 digit number less than 100* Location= *character string length upto 30*
User Interface The means by which the user and a computer system interact, in particular the use of input devices and software. Provide a means of: Input, allowing the users to manipulate a system, and/or Output, allowing the system to indicate the effects of the users manipulation.
Conclusion References: Data Flow Diagrams http://en.wikipedia.org/wiki/Data_flow_diagram Agile Modeling http://www.agilemodeling.com/artifacts/dataFlowDiagram.htm EDrawSoft – Data Flow Diagrams http://www.edrawsoft.com/Data-Flow-Diagrams.php Data flows: Note on Data-Driven Process Modeling http://faculty.babson.edu/osborn/mis7520/readings/dfddiag.htm
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