ASSIGNMENT IN COMPUTER LECTURE

What is a DFD?
Data Flow Diagramming is a means of representing a system at any level of detail with a graphic network of symbols showing data flows, data stores, data processes, and data sources/destinations.
When it comes to conveying how information data flows through systems (and how that data is transformed in the process), data flow diagrams (DFDs) are the method of choice over technical descriptions for three principal reasons. * DFDs are easier to understand by technical and nontechnical audiences * DFDs can provide a high level system overview, complete with boundaries and connections to other systems * DFDs can provide a detailed representation of system components DFDs help system designers and others during initial analysis stages visualize a current system or one that may be necessary to meet new requirements. Systems analysts prefer working with DFDs, particularly when they require a clear understanding of the boundary between existing systems and postulated systems. DFDs represent the following: * External devices sending and receiving data * Processes that change that data * Data flows themselves * Data storage locations
The hierarchical DFD typically consists of a top-level diagram (Level 0) underlain by cascading lower level diagrams (Level 1, Level 2…) that represent different parts of the system.

What are the symbols used in DFD?
DFDs consist of four basic components that illustrate how data flows in a system: 1. Entity

2. Process

3. Data Store

4. Data Flow
Entity- An entity is the 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 (referred to as a sink). 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). Entities are also referred to as agents, terminators, or source/sink.
Process- The process is the manipulation or work that transforms data, performing computations, making decisions (logic flow), or directing data flows based on business rules. In other words, a process receives input and generates some output. Process names (simple verbs and dataflow names, such as “Submit Payment” or “Get Invoice”) 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.
Data Store- A data store is 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 (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 Flow- Data flow is the 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.