5:00-6:00/CS2/209/MWF

Name: Joanna Marie Samonte Date: July 05, 2010

Professor: Mrs. Neypes Rating:

ASSIGNMENT # 02

Data Flow Diagram

Definition

A two-dimensional diagram that explains how data is processed and transferred in a system. The graphical depiction identifies each source of data and how it interacts with other data sources to reach a common output. Individuals seeking to draft a data flow diagram must (1) identify external inputs and outputs, (2) determine how the inputs and outputs relate to each other, and (3) explain with graphics how these connections relate and what they result in. This type of diagram helps business development and design teams visualize how data is processed and identify or improve certain aspects. Larry Constantine is credited with designing the basic design of the data flow diagram. (www. businessdictionary.com)

A data-flow diagram (DFD) is a graphical representation of the "flow" of data through an information system. DFDs can also be used for the visualization of data processing (structured design).

On a DFD, data items flow from an external data source or an internal data store to an internal data store or an external data sink, via an internal process.

A DFD provides no information about the timing of processes, or about whether processes will operate in sequence or in parallel. It is therefore quite different from a flowchart, which shows the flow of control through an algorithm, allowing a reader to determine what operations will be performed, in what order, and under what circumstances, but not what kinds of data will be input to and output from the system, nor where the data will come from and go to, nor where the data will be stored (all of which are shown on a DFD). (www.wikipedia.org)

A data flow diagram (DFD) is a significant modeling technique for analyzing and constructing information processes. DFD literally means an illustration that explains the course or movement of information in a process. DFD illustrates this flow of information in a process based on the inputs and outputs. A DFD can be referred to as a Process Model.

Additionally, a DFD can be utilized to visualize data processing or a structured design. A DFD illustrates technical or business processes with the help of the external data stored, the data flowing from a process to another, and the results.

A designer usually draws a context-level DFD showing the relationship between the entities inside and outside of a system as one single step. This basic DFD can be then disintegrated to a lower level diagram demonstrating smaller steps exhibiting details of the system that is being modelled. Numerous levels may be required to explain a complicated system.(www.edrawsoft.com)

Data Flow Diagram Notation

(www.wikipedia.com) (www.smithsrisca.demon.co.uk) (www.conceptdraw.com)

Externals: These are where the flow of information begins and ends. There are two types of external, namely information sources (where the information comes from), and information destinations (where it goes to once it has been processed). The output information will usually be different in some key respect to the input information, otherwise there would be no value in carrying out the process. There is no theoretical limit to how many externals are allowed, but in practice there will usually be one or two sources, and one or two destinations.

Processes: These are where things happen to the information in transit through a system. This might involve storing it as it stands or amending it in some way. It might also involve making decisions on the basis of that information. One of the most useful "rules" of DFDs is that processes must always be nameable, because the act of being able to name them gives you a valuable clue as to whether you really understand what they are doing.

Stores: These are where information is stored until needed. They are the filing cabinets in the system's internal filing system, so to speak. As with biological memory, they can be for either short or long term storage of information. They can also be for the exclusive use of a single process, or else the common use of a number of processes. Under this latter heading, it is common to find one process writing to a store, and then a subsequent process reading from it.

Information Flows: These are the routes taken by the information en route from its source to its destination. Specifically, there will be flowlines between information sources and the initial processes, between process and process, and between process and store. Should information need to flow both ways in a particular instance, then it may be shown either as a double-headed single flow or (preferably) as two opposed single-headed flows. Some practitioners also scale the width of the flow lines to indicate the relative intensity of traffic along them. (www.smithsrisca.demon.co.uk)

Data flow diagrams consist of following components:

Processes and functions which represent actions happened in information system;

External entities which represent in the system data ingoing and outgoing from it;

Data depositories which represent places in system where data can be saved for definite period of time;

Data flows, indicating direction and character of data flowing in the considered information system. www.conceptdraw.com

Data Flow Diagram Example

(www.visualcase.com) (www.conceptdraw.com)

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