System Analysis and Design M Umair www.m-umair.com
System Description Techniques Graphical representation of any process is always better and more meaningful than its representation in words. System Analysis and Design makes use of the various tools for representing and facilitating comprehension of the complex processes and procedure involved. Ref: System Analysis & Design by Dennis, Wixom, Roth.
Data Flow Diagram - DFD Data flow diagrams are the most commonly used way of documenting the process of current and required systems. As their name suggest, they are a pictorial way of showing the flow of data into, around and out of a system. Ref: System Analysis & Design by Dennis, Wixom, Roth.
Data Flow Diagram - DFD Graphical representation of a system s data and how the process transform the data is known as Data Flow Diagram (DFD). DFDs do not give detailed descriptions of modules but graphically describe a system s data and how the data interact with the component of a system. Ref: System Analysis & Design by Dennis, Wixom, Roth.
Components of DFD DFDs are constructed using four major components External entities Data stores Processes Data flows Ref: System Analysis & Design by Dennis, Wixom, Roth.
Components of DFD External Entities External entities represent the sources of data as input to the system. They are also the destination of system data. External entities can be called data stores out side the system. Ref: System Analysis & Design by Dennis, Wixom, Roth.
Components of DFD Data Stores Data stores represent stores of data within the system. Examples, computer files or databases. An open-ended box represents a data, which implies store data at rest or a temporary repository of data. Ref: System Analysis & Design by Dennis, Wixom, Roth.
Components of DFD Processes Processes represents activities in which data is manipulated by being stored or retrieved or transferred in some way. In other words, we can say that process transforms the input data into output data. Circles stand for a process that converts data into information. Ref: System Analysis & Design by Dennis, Wixom, Roth.
Components of DFD Data Flows Data flow represents the movements of data from one components to the other. An arrow identifies data flow data in motion. It is a pipeline through which information flows. Data flows are generally shown as one-way only. Data flows between external entities are shown as dotted lines. Ref: System Analysis & Design by Dennis, Wixom, Roth.
Symbols of DFD Ref: Lucidchart
DFD Levels Ref: http://inls382.web.unc.edu
DFD - Context Diagram Context diagram The context diagram is the DFD of the scope of an organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between the external entities and the system. Ref: http://inls382.web.unc.edu
DFD - Context Diagram Ref: http://inls382.web.unc.edu
DFD Level-0 Diagram Level-0 diagram The level-0 diagram is a DFD that represents a system s major processes, data flows and data stores at a high level of detail. Ref: http://inls382.web.unc.edu
DFD Level-0 Diagram Ref: http://inls382.web.unc.edu
DFD Level-1&2 Diagram Going on, decomposition step by step, level-1 diagrams, level-2 diagrams and so forth are developed. Task : Decompose the level-0 diagram into level-1 diagram. Refer the example I solved over the white board. Ref: http://inls382.web.unc.edu
Modeling Process of DFD Creating a DFD is a highly iterative process of gradual refinement. The general steps are 1. Create a preliminary Context Diagram. 2. Identify Use Cases, i.e., the ways in which users most commonly use the system. 3. Create DFD fragments for each use case. 4. Create a level-0 diagram from fragments. 5. Decompose to level 1, 2,... 6. Go to step (1) and revise as necessary. 7. Validate the DFDs with users. Ref: http://inls382.web.unc.edu
More examples of DFD For more examples refer to DFDs I have drawn on white board during the lecture.