System Documentation: Use Case & ER Diagrams

Study Notes

Focuses on use case diagrams, entity relationship diagrams, and dataflow diagrams for system documentation.

Purpose: Clearly defines the scope of a system by specifying who will use it and what they will use it for.
Symbols:
- Actor: Represents a user of the system.
- Activity/Use Case: Represents an action a user can perform with the system.
Special Relationships:
- Includes: An activity that must occur if the related activity is performed by the actor.
- Extends: An activity that may occur if the related activity is performed by the actor.

Purpose: Identifies and communicates key components of a system, their attributes, and relationships between them.
Shapes:
- Entity: Represents a key component of the system (e.g., Customer, Product).
- Relationship: Represents the connection between entities.
- Attribute: Represents a characteristic of an entity (e.g., Customer Name, Product Price).
- Generalization (IS-A): Represents a hierarchical relationship between entities.

One-to-One (1:1): One instance of an entity is related to only one instance of another entity.
One-to-Many (1:M): One instance of an entity is related to multiple instances of another entity.
Many-to-Many (M:M): Multiple instances of an entity are related to multiple instances of another entity.

Aggregation: Refers to an entity having a relationship with an existing relationship.

Purpose: Captures the movement and transformation of data within a system.
Shapes:
- System User: Represents users interacting with the system.
- Process: Represents a task or step in the system.
- Data Flow: Represents the movement of data within the system.
- Data Store: Represents a location where data is stored (a database, file, etc.).
Data Flows: Illustrate movement of data between processes; from processes to data stores and vice versa.
Correct and Incorrect Data Flows: Diagram examples show how data flows should be and common pitfalls.