DFD illustrates the inputs, outputs, how the data flows through the system and where data will be stored. On the other hand, a flowchart helps to illustrate the steps to solve the problem. It can be used as the basis to write the program.
What is a Flowchart — Definition, Functionality 3. It represents how a system processes data and describes where the data comes from, where it goes and how the data is stored. DFD became popular during the year There are two types of notations for DFD. They are the Yourdon and Coad, Gane and Sarson. Youdon and Coad — This type of diagrams are used for system analysis and design.
Circles represent the processes. Gane and Sarson — This type of diagrams are used for information systems. Square with round corners represent the processes. Process — Transforms incoming data flow into the outgoing data flow. Data Store — Represents the repositories of data in the system. Data Flows — Represents the pathway of data flow.
External Entities — Represents the objects outside the system. The system communicates with these external entities. What is logic modeling? How to use structured English , decision tables , and decision trees for logic modeling? What is a systems proposal and its role in systems analysis? Data flow -- data moves from one place of the system to another 2. Data store -- data at rest 3. Condition Recommendation Many repetitious actions Structured English Communication to end users is important Structured English Complex combinations of conditions, actions and rules Decision tables Checking for redundancies, contradictions, possibilities Decision tables The sequence of conditions and actions is critical Decision tree Not every condition is relevant to every action Decision tree Evolution of systems analysis techniques Era Orientation Techniques Evaluation Pre-computer Flow-oriented, i.
Context diagram. External entity. Data flow. Data store. How the business operates. How the system will be implemented. Business activities. Programs, program modules, manual procedures. Collections of data. Physical files and databases, manual files. Type of data store. Permanent data collections. Master files, transaction files. System controls. Business controls. Controls for data validation, record status, system security.
Data types. Specific description. It breaks a process down to a finite number of steps that get executed one at a time. Thus, if the flowcharts accurately describe the content carried out within them in the diagram, they can be used for analysis. It actually does not say anything about what the inputs and outputs of each step are. It does not address how each step performs internally. Flowcharts will be the useful diagramming tools for the system analysis activity when it is concerned with the user implementation.
The users, the system analysts and the implementation team can discuss those implementation constraints that must be imposed upon the system. They, for example, can determine the boundary of the system and the details of the interaction between the systems and the users.
However, there are several reasons that most system analysts actually do not use detailed flowcharts for process specifications. Flowcharts are composed of many symbols but the common flowcharts are composed of three basic symbols: Arrows, Diamonds and Rectangles.
Unlike Data Flow Diagrams which are used to describe data flow within the system, flow charts are typically used to describe the detailed logic of a business process or business rule.
Figure 1: The example of the Flow Chart. Data flow diagram is a graphical representation of the flow of data through an information system. Rather than showing the strict order of execution of steps, it shows how processes depend on one another for information. System analysts use it as a tool for modeling and analyzing the processes in the system. It helps analysts to visualize the data processes since data enter to the system, and then they are used by the system until they are returned to the environment.
Analysts also use DFDs to study alternative information handling procedures during the process of designing new information services. In addition, Data Flow Diagrams can be used for compared the new system and the old system. With this comparison, system analysts can find the gap between two systems and the effectiveness of the improved system.
Although Data Flow Diagram is one of the power tools for analyzing the systems, the system analysts must keep in mind that it provides only one view of the system. It focuses mainly on the function-oriented view. So, if the systems are more concerned with data relationships than the functions, Data Flow Diagram will be less important. Instead, system analysts must concentrate mainly on developing the Entity-Relationship Diagrams.
Alternatively, the State-Transition Diagrams will be the most importance if the time-dependent behavior of the system dominated all other issues. A data flow diagram illustrates the processes, data stores, and external entities in a business or other system and the connecting data flows. Some examples of the procedural questions are what the criteria for moving data from one process to another process and what the order in which the processes are performed.
Furthermore, there are several common modeling rules that you need to follow when creating Data Flow Diagrams. In the real projects, data flow diagrams are considerably large and complex. So we need to avoid drawing the whole system in only one diagram. System analysts organize the overall DFD in a series of levels so that each level provides successively more detail about a portion of the level above it. It consists of only one circle representing the entire system, the data flows showing the interaction between the system and the external terminators.
There is no data stores appear on a context diagram because the data stores of the systems are conceptually inside the one process. The context diagrams are useful for showing how a proposed system may behave for a specific example or scenario. Level-0 diagram is the decomposition of the one process from the context diagram into two to nine high-level processes. Then, each process in the Level-0 diagram can be decomposed into the next level.
In order to properly create many levels of data flow diagram, you must understand two concepts: decomposition and balancing. Figure 2: The example of the Data Flow Diagram. It shows how a system interacts with the external entities.
So, it is relatively sparse about the details of how the system behaves internally and how the external environment is configured.
Indeed, Use Case Diagram shows what we want the system to do rather than describe how it can be accomplished. One of the major benefits of this diagram is communication. Those actions must provide the measurable value to an actor. It is represented by horizontal ellipse. Furthermore, it can be networks, communication devices, computers, or other programs on the same computer. It is represented by stick figure. It is represented by lines connecting between use cases and actors with an optional arrowhead on one end of the line.
Notice that the arrowheads in Use Case diagram is used for indicating the direction of the initial invocation of the relationship or to indicate the primary actor, while the arrowheads of Data Flow Diagram is used for showing the flow of data in the system.
Anything within this boundary is the functionality in scope of the system. System analysts and designers must remember that interaction among actors is not shown in the Use Case Diagrams. Thus, the system boundary should reexamine if the interaction between actors is essential to a coherent description of the desired behavior.
Furthermore, Actors are formed based on the role we set. So, the different actors may actually be the same person. Figure 3: The example of the Use Case Diagram. Entity-Relationship Diagrams is a network model that describes the stored data layout of a system at a high level of abstraction.
Since Data Flow Diagram mainly focuses on the function that the system perform not the data that the system need, using Entity-Relationship Diagram is important to capture another part of system analysis which concentrates mainly on the data in the system.
Entities are represented by rectangles. It has three main characteristics. First, each entity can be identified uniquely in some way. Student, for example, must be able to distinguish from one another by student identities, or name because if students are the same, then Student is meaningless in Entity-Relationship Diagram. Second, each entity must play a necessary role in the system.
In other words, objects which have no role in the system can not put into the system.
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