System Modeling Essentials: UML Perspectives & Diagrams
What is System Modeling?
Process of creating abstract graphical models of a system.
Goal: Understand and communicate different views (perspectives).
Common Language: UML (Unified Modeling Language)
Four System Perspectives
| Perspective | Description |
|---|---|
| External | Models the system environment or context |
| Interaction | Shows how system components or users interact |
| Structural | Shows how the system or data is organized |
| Behavioral | Shows how the system behaves or reacts to events |
Context Models
Show the operational context of a system.
Help define system boundaries:
What’s inside or outside the system.
Affects requirements and organizational politics.
Importance of Context Diagrams:
Scope Definition
Requirements Gathering
Communication
Risk Identification
Process Perspective
Goes beyond the environment view: shows how the system is used in business processes.
Uses Activity Diagrams (UML) to represent flow.
Activity Diagrams
Show control flow: sequential or concurrent activities.
Represent how actions are triggered.
Used to describe business logic or workflow.
Interaction Models
Help identify user/system requirements and performance issues.
Utilize:
Use Case Diagrams
Sequence Diagrams
Use Case Modeling
Use cases are tasks involving external interaction with the system.
Actors are people or systems interacting with the system.
Key Components:
Actor: Named by a noun
Use Case: Named by verb + noun (e.g., View Grades)
Communication Link: Solid line showing interaction
Relationships in Use Case Diagrams
| Relationship | Meaning |
|---|---|
| Include | One use case includes another use case’s functionality |
| Extend | A use case can add behavior to another use case under specific conditions |
| Generalization | One use case is a specialized version of another |
Example Use Case: Mentcare System Data Transfer
| Field | Description |
|---|---|
| Actors | Medical receptionist, patient records system |
| Stimulus | User command |
| Response | PRS updated confirmation |
| Data | Personal info, treatment summary |
| Comments | Receptionist needs permission |
Sequence Diagrams
Part of UML: models interactions in time order.
Shows how actors and objects communicate.
Key Elements:
Lifeline (object timeline)
Messages (annotated arrows)
Steps to Create Sequence Diagrams
Identify the use case.
List participants.
Define and arrange lifelines.
Add messages and returns.
Indicate order, timing, and add annotations.
Example: Emotion-Based Music Player Sequence
Captures user’s image → detects emotion → retrieves mood/music → displays playlist
Structural Models
Focus on a system’s components and their relationships.
Types of Structural Models:
Static (design-time structure)
Dynamic (run-time organization)
Class Diagrams
Used in Object-Oriented Design.
Key Elements:
Classes
Attributes
Methods
Relationships (association, aggregation, etc.)
Classes represent real-world concepts (e.g., Patient, Doctor).
Behavioral Models
Show how the system responds to events or data.
Two Main Stimuli Types:
Data-driven (e.g., input triggers processing)
Event-driven (e.g., external or internal triggers)
Data-Driven Modeling
Common in business systems.
Models sequence of actions based on input to output.
Used to show end-to-end processing.
Event-Driven Modeling
Common in real-time systems.
Models reactions to specific events.
Based on finite-state machines.
State Machine Models
Represent how a system transitions between states.
Used for real-time and control systems.