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Data Flow Diagram, Data Dictionary

 Data flow diagrams (DFDs) and data dictionaries are fundamental tools used in system analysis and design. They work together to visually represent the flow of data through a system and define the characteristics of that data.

Data Flow Diagram (DFD)

A DFD is a graphical representation of how data moves through a system. It shows the processes that transform data, the data stores that hold the data, the external entities that interact with the system, and the data flows that connect these elements.

Here are the four main symbols used in a DFD:

  • Process: A rounded rectangle represents a process that transforms data.
  • Data Flow: An arrow represents the flow of data between processes, data stores, and external entities.
  • Data Store: A rectangle with two parallel lines represents a data store that holds data.
  • External Entity: A square represents an external entity that interacts with the system.

Data Dictionary

A data dictionary is a centralized repository that defines the data elements used in a system. It provides detailed information about each data element, such as its name, data type, size, description, and allowed values.

Here are some of the benefits of using DFDs and data dictionaries:

  • Improved communication: DFDs and data dictionaries provide a common language for system analysts, designers, and developers.
  • Better understanding of systems: DFDs help to visualize the flow of data through a system, which can help to identify potential problems and areas for improvement.
  • Data quality: Data dictionaries help to ensure that data is used consistently and accurately throughout a system.

Let's look at an example of how DFDs and data dictionaries can be used together.

Consider a library system. A DFD for this system might show the following processes:

  • Check out book
  • Return book
  • Add new book
  • Update book information

The data flows between these processes might include:

  • Borrower ID
  • Book ID
  • Due date
  • Book title
  • Author

A data dictionary for this system would define each of these data elements, such as:

  • Borrower ID: A unique identifier for each borrower.
  • Book ID: A unique identifier for each book.
  • Due date: The date by which a borrowed book must be returned.
  • Book title: The title of a book.
  • Author: The author of a book.

By using DFDs and data dictionaries together, system analysts and designers can create a clear and concise understanding of how data flows through a system. This can help to improve the quality and efficiency of the system.

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