Although this may be the case in implementation level as some of the DBMS do support the use of functions, which intake some values as parameters and return a result, in Data Flow Diagram, we tend to treat data store as a sole data holder that does not possess any processing capability. When we label a data flow that ends at a data store "a request", this literally means we are passing a request as data into a data store. Connectors in a Data Flow Diagram are for representing data, not for representing process flow, step or anything else. Keep in mind that Data Flow Diagram was designed for representing the exchange of information. Some of them will try to represent a request by adding a connector between a process and a data store, labeling it "a request" or "request for something", which is wrong. Some designers may feel uncomfortable when seeing a connector connecting from a data store to a process, without seeing the step of data request being shown on the diagram somehow. So it really depends on the purpose of your design. However, using general terms can be kind of lacking details and make the design lost it usefulness. The use of general terminologies like "details", "information", "credential" certainly leave room for discussion. In most cases, Data Flow Diagram is drawn in the early phase of system development, where many details are yet to be confirmed. What if we write them explicitly as "rental date, video rented, person rent", "video id, video name and video status"? Is this correct? Well, there is no definite answer to this question but try to ask yourself a question when making a decision. In this Data Flow Diagram example, the word "info" is used many times when labeling data. Data Flow Diagram Tips and Cautions Be aware of the level of details If this information is important and worth mentioning, consider to model it with diagrams like BPMN Business Process Diagram or UML Activity Diagram.įinally, a Manager can receive Rental report from the Generate Rental Report process and the information involved is provided by the Rental data store. Note that Data Flow Diagram does not answer in what way and in what order the information is being used throughout a system. and produces Video info., Rental info., and Return receipt, with no order specified. Strictly speaking, the diagram only tells us the Return Video process receives Video & Rental info. It is our common sense that lead us to interpret the diagram in the way that we understand it naturally. Although we said that the receipt is delivered as a result of the Return Video process, the Data Flow Diagram implies no such thing. As a result, Return receipt is delivered to the Customer. into the Video Library data store and Rental info. into the Rental data store.Ī Customer can Return Video by providing Video & Rental info. As a result, the process produces a Bill to the Customer, and stores the Rental info. The Rent Video process also receives Video info. Although there is no design guideline that governs the positioning of shapes in a Data Flow Diagram, we tend to put the processes in the middle and data stores and external entities on the sides to make it easier to comprehend.īased on the diagram, we know that a Customer makes a Video request to the Rent Video process. The Video Rental System Data Flow Diagram example contains three processes, two external entities and two data stores. Read through the diagram and then we will introduce some of the key concepts based on this diagram. break down) of the video rental system that is shown in the context DFD. The figure below shows the level 1 DFD, which is the decomposition (i.e. It contains one and only one process and does not show any data store, which makes the diagram simple. In between the process and the external entities, there are data flow connectors indicating the existence of information exchange between customer and the system.Ĭontext DFD is the entrance of a data flow model. In this example, there are two external entities, namely Customer and Manager. It also shows the participants who will interact with the system, called the external entities. It contains a process (shape) that represents the system to model, in this case, the " Video Rental Store". The figure below shows a context Data Flow Diagram that is drawn for a video rental system. The Video Rental System Example Context DFD
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