Data Flow Diagram Concepts

Data Flow Diagram (DFD)

• Provides a graphical representation of a system, accessible to both technical and non-technical users.
• Describes the data transfer process within a system, from input to storage and report generation.

Entities

• Represent individuals, organizations, or objects that interact with the system.
• Entities are external to the information system, but play a role in the process.

Processes

• Actions that directly modify data.
• They produce output based on the performed action.
• Common processes include calculations, data sorting, and business rules.

Data Flow

• Lines with arrows that show the direction of data movement.
• They map the input and output generated by entities interacting with data stores.

Data Stores

• Files or storage areas holding information for later retrieval.
• Examples include database tables or spreadsheets.
• They are labeled to indicate their purpose or order.

Data Flow Rules

• Data cannot flow directly between two entities.
• Data must move through a process before moving to another entity.
• Data cannot flow directly between two data stores.
• Data must be processed before moving from a data store to another.
• Data flow from an entity must be processed before reaching a data store (and vice versa).

Applications of DFDs

• Software Engineering: Provides structure for system design and aids application architecture.
• Agile Development: Helps developers visualize and build on existing work.
• Business Analysis: Provides a framework to analyze existing systems and identify inefficiencies.

Levels of DFDs

• Level 0 Context Diagram:
  • Represents the entire system as a single process.
  • Shows high-level inputs and outputs.
  • Does not include data stores.
• Level 1 Overview Diagram:
  • Utilizes all four DFD elements.
  • Limits the number of processes to 9-10.
• Level 2 Overview Diagram:
  • Breaks down processes in further detail.
  • Introduces more specific data stores.

Use Case Diagram

• A behavioral UML diagram used to analyze systems.
• Visualizes roles within a system and their interactions.

UML (Unified Modeling Language)

• A standardized modeling language for specifying, visualizing, constructing, and documenting software systems.
• Also applicable for business modeling and non-software systems.

Use Case Diagram Elements

• System: Defines the scope of the use case, represented as a rectangle.
• Actor: Any entity (person, organization, or external system) performing a role in the system.
• Use Case: A function or action within the system, represented as an oval and named with the corresponding function.
• Communication Link: A solid line connecting an actor to a use case, signifying communication.
• Relationship: Illustrates relationships between actors and use cases with simple lines, arrows, or labels.

When to Use Include

• The base use case is incomplete without the included use case.
• The included use case is a mandatory, non-optional process.

When to Use Extend

• The extending use case is usually a conditional process.
• The main use case can function without the extending use case.

Relationship Rules

• Two or more base use cases can be included in one sub-use case.
• Relationships are only allowed between main and sub-use cases.