In the last assignments 8 and 9, we were told to make a data flow diagram of pre-Enrollment system of the University of the Southeastern Philippines. The diagrams I made describe the flow of the pre-enrollment system of the school. In making a data flow diagram, we should first analyze the system thoroughly. A system analyst must know and understand on how to create data flow diagram. When we are evaluating a particular system, we have to analyze each process involve in the system. As what we have said from the previous assignments, a system analyst must know how to analyze and understands. Data flow diagrams can help to explain the flow of the system and its processes. In the assessment, we will discuss about Data flow diagram.
First, let us define Data flow diagram, 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. In the year 1970, data flow diagram was developed and enhanced by the likes of Yourdon, McMenamin, Plamer, Gane and Sarson. It is one of the primary tools of the structured analysis. Now, it is still considered as one of the best modeling techniques for and representing the processing requirements of a system. Data Flow Diagram is also an important technique for modeling a system’s high-level detail by showing how input data is transformed to output results through a sequence of functional transformations. Data flow diagrams reveal relationships among and between the various components in a program or system. A Data Flow Diagram is also a diagrammatic representation of the information flows within a system, showing how information enters and leaves the system, what changes the information and where information is stored.
In making data flow diagrams, there are symbols that we will use. There are rectangular box, arrow headed lines, bubble or circle or round corner square and the narrow opened rectangle.
· Rectangular box - External Entities
- Source or destination of data. The source in a DFD represents these entities that are outside the context of the system. Entities either provide data to the system (referred to as a source) or receive data from it. Entities are often represented as rectangles (a diagonal line across the right-hand corner means that this entity is represented somewhere else in the DFD)
- can be people, departments, other companies, other systems
- are called sources if they are external to the system and provide data to the system, and sinks if they are external to the system and receive information from the system
· Arrow headed lines - Data Flow
- Movement of data between the entity, the process, and the data store. Data flow portrays the interface between the components of the DFD. The flow of data in a DFD is named to reflect the nature of the data used (these names should also be unique within a specific DFD). Data flow is represented by an arrow, where the arrow is annotated with the data name.
- must originate from and/or lead to a process (this means that entities and data stores cannot communicate with anything except processes –remember that it takes a process to make the data flow)
- can go from process to process, but that does imply that no data is stored at that point
- can have one arrowhead indicating the direction in which the data is flowing
- Can have 2 arrowheads when a process is altering (updating) existing records in a data stores.
· Bubble (Circle or round corner square) – Process
- Manipulation or work that transforms data, performing computations, making decisions or logic flow, or directing data flows based on business rules. In other words, a process receives input and generates some output. Process names usually describe the transformation, which can be performed by people or machines. Processes can be drawn as circles or a segmented rectangle on a DFD, and include a process name and process number.
- must have at least one input and at least one output
- at the primitive level are labeled with verb + object (example of this, “print invoice” or “add customer”)
- at the non-primitive level, are labeled more generally (example of this, “customer maintenance” or “warehouse reports”)
· Narrow opened rectangle - Data Store
- Where a process stores data between processes for later retrieval by that same process or another one. Files and tables are considered data stores. Data store names in plural are simple but meaningful, such as “customers,” “orders,” and “products.” Data stores are usually drawn as a rectangle with the right hand side missing and labeled by the name of the data storage area it represents, though different notations do exist.
- data is stored whenever there are more than one process that needs it and these processes don’t always run one after the other (if the data is ever needed in the future it must be stored)
- are labeled with a noun (example of this is the label “customers” indicates that information about customers is kept in that data store)
The basic principle for creating a DFD is that one system may be split into subsystems, which in turn can be disintegrated into subsystems at a much lower level, and so on and so forth. Every subsystem in a Data flow diagram represents a process. In this process or activity the input data is processed. Processes cannot be disintegrated after reaching a certain lower level. Each processes in a Data flow diagram characteristic an entire system. In a Data flow diagram system, data is introduced into the system from the external environment. Once entered the data flows between processes. And then the processed data is produced as an output or a result. When we talk about how information data flows through systems and how that data is transformed in the process, data flow diagrams are the method of choice over technical descriptions for three principal reasons: Data flow diagrams are easier to understand by technical and nontechnical audiences; Data flow diagrams can provide a high level system overview, complete with boundaries and connections to other systems and; Data flow diagrams can provide a detailed representation of system components.
Data flow diagrams help system analyst and others during the planning or the analysis stages visualize a current system or one that may be necessary to meet new requirements. Systems analysts prefer working with data flow diagrams, particularly when they require a clear understanding of the boundary between existing systems and postulated systems. Data flow diagrams represent the following: External devices sending and receiving data; Processes that change that data; Data flows themselves; Data storage location.
According to Hubpages, in using data flow diagram, there are advantages and disadvantages.
Advantages:
- It gives further understanding of the interestedness of the system and sub-systems
- It is useful from communicating current system knowledge to the user
- Used as part of the system documentation files
- Dataflow diagram helps to substantiate the logic underlining the dataflow of the organization
- It gives the summary of the system
- Data flow diagram is very easy to follow errors and it is also useful for quick reference to the development team for locating and controlling errors
Disadvantages:
- A simple but powerful graphic technique which is easily understood.
- Represents an information system from the viewpoint of data movements, which includes the inputs and outputs to which people can readily relate.
- Data flow diagram is likely to take many alteration before agreement with the user
- Physical consideration are usually left out
- Helps to define the boundaries of the system.
- It is difficult to understand because it ambiguous to the user who have little or no knowledge
In making a data flow diagram, there are general rules to follow:
· Any data flow leaving a process must be based on data input to the process.
· All data flows are named; the name reflects that data flowing between processes, data stores, sources and sinks.
· Only data needed to perform the process should be an input to the process.
· A process should know nothing about, that is, be independent of any other process in the system; it should depend only on its own input and output.
· Processes are always running; they do not start or stop. Analysts should assume a process is always ready to function or perform necessary work.
Data flow diagram is a highly effective technique for showing the flow of information through a system. Data flow diagrams are used in the preliminary stages of systems analysis to help understand the current system and to represent a required system. In this way, system analyst can easily understand the flow of the system. By using data flow diagrams, it can explain the flow of the system using visualization. It also helps to find some problems of the system. Data flow diagrams also can help to visualize the data going. It also describes all the process of the system and what the process does. That is why Data flow diagram considered as the best modeling techniques for and representing the processing requirements of a system.
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