Question

Create a DFD (Context and Level 0) for a Car Servicing Center.

Model the login process for walk-in customers. These customers can be “new” or

“existing”. All new customers must be first registered. Each customer may own

multiple vehicles, and all vehicles need to be assigned to a “Mechanic” based on

schedule and availability. Each vehicle may have one or more service requests. Some

services might require ordering of parts from a supplier. Post servicing, the

customers will make payments, as needed. All service requests are stored such that

Management can review periodic reports for performance evaluation.

Answer 1

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Context DFD

The figure below shows a context Data Flow Diagram drawn for a vehicle maintenance depot system. It contains a process (shape) that represents the system to model, in this case, the "vehicle maintenance depot system". It also shows the participants who will interact with the system, called the external entities. In this example, Customer and Mechanics are the entities who will interact with the system. In between the process and the external entities there are data flow (connectors) that indicate the existence of information exchange between the entities and the system.

Context DFD is the entrance of a data flow model. It contains one and only one process and does not show any data store.

Level 1 DFD

The figure below shows the level 1 DFD, which is the decomposition (i.e. break down) of the system shown in the context DFD. Read through the diagram, and then we will introduce some of the key concepts based on this diagram.

The Data Flow Diagram example contains three processes, two external entities and three data stores. Although there is no design guidelines 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.

Based on the diagram, we know that the Perform Inspection process provides Bill to the Customer and store the Inspection result into the Inspection data store.

The Perform Maintenance/Repairing process takes Inspection result from Inspection data store as input, and provides the Customer with the Bill. Besides, Work detail is stored in the Work Record data store and Parts info. is stored in the Parts Inventory data store. Note that Data Flow Diagram does not represent the order of data flow. Strictly speaking, this diagram only tells us the Perform Maintenance/Repairing process receives Inspection result as input and produce Bill, Work detail and Part info., with no order specified. Keep in mind that Data Flow Diagram does not answer in what way and in what order the information is being used throughout a system. If this information is important and worth mentioning, consider to model it with diagrams like BPMN Business Process Diagram or UML Activity Diagram.

A Mechanics can Order Parts by providing Parts info., and the result is the storage of Parts info. in the Parts Inventory data store. The process also receives Parts info. from Work Record data store throughout the process.

Data Flow Diagram Tips and Cautions