Data Flow and Use Case Diagrams: Systems Analysis Essentials

Data Flow Diagrams (DFD)

A Data Flow Diagram is a tool that allows for the graphical analysis and representation of an organization's processes.

Core DFD Elements

• Process: Indicates the actions the system must perform. It must have at least one input and one output, and the name should begin with an infinitive verb.
• Entities: All actors connected to the system, such as departments, organizations, or other systems.
• Files: Clusters of information that store data within the organization.
• Flow: Indicates the data moving through processes, representing inputs and outputs.

Common DFD Anomalies

• Black Hole: A process that only receives information and does not send any.
• Miracle: A process that only sends information without receiving any.

Object-Oriented Design Concepts

The following concepts define the structure of object-oriented systems (e.g., Library Control Systems):

• Classes: A generalization of object characteristics.
• Objects: An instance of a class.
• Inheritance: Key features passed from a parent class to a child class; this is unidirectional.
• Aggregation: Adding features to a class or object without inheritance.
• Polymorphism: When a transaction shares the same name across different classes, with each class knowing how to execute it.
• Abstraction: Separating and modifying characteristics without needing to understand the entire system functionality.
• Encapsulation: Hiding the internal functionality of an object, focusing only on the generated results.
• Multiplicity: The relationship between classes (e.g., 1-M, 1-1, M-M).

Use Case Diagrams

A Use Case Diagram is an object-oriented design tool used to graphically represent system actions.

Use Case Elements

• Actors: External entities related to system processes.
• Use Case: Activities performed by the system from the actor's perspective.
• Relations:
  • <<Include>>: Indicates a use case that must be run every time the principal use case is executed.
  • <<Extend>>: Represents an optional relationship that does not necessarily run every time the principal use case is executed.