Unified Modeling Language (UML)
Reference: UML Diagrams
Background
Prior to UML...
- Different notations and diagrams
- Everyone confused
Now, with UML...
- Created by Grady Booch, Ivar Jacobson, and James Rumbaugh in 1997
What is UML?
Not a programming language
- Set of diagrams and notations used to model software systems.
- Universal, culture invariant, and so much fun!
Hooray standards!
Do We Really Need to Know All This?
Per IBM: An introduction to the Unified Modeling Language:
The most useful, standard UML diagrams are: use-case diagram, class diagram, sequence diagram, statechart diagram, activity diagram, component diagram, and deployment diagram.
Different domains use some more than others.
When to Use UML
- Planning new systems / functionality
- Documenting existing systems
- Training new team members
- Communicating with stakeholders
- Safety critical systems
- Regulatory compliance
Diagram Types
Use Case Diagram
Description
- Represent functionality, actors, and how these relate to each other in the context of a system.
- "High level" scope; not much detail.
- Useful for planning new functionality.
- Useful for communicating with stakeholders.
Key components
- Actors
- Use cases
-
Relationships between actors and use cases
- *Optionally, relationships between use cases (includes / extends)
- System boundaries
Class Diagram
Description
- Shows how entities (classes) in a system relate to each other.
- Classes contain self-describing attributes and methods.
-
Connectors between classes show cardinality; how many
of one class can be related to another class.
- https://www.uml-diagrams.org/multiplicity.html
- Also... Crow's feet notation.
| Multiplicity | Option | Cardinality |
|---|---|---|
| 0..0 | 0 | Collection must be empty |
| 0..1 | No instances or one instance | |
| 1..1 | 1 | Exactly one instance |
| 0..* | * | Zero or more instances |
| 1..* | At least one instance | |
| 5..5 | 5 | Exactly 5 instances |
| m..n | At least m but no more than n instances |
-
Entities can be concrete or abstract. From above:
-
Concrete examples:
- Person
- ??? (what else?)
-
Abstract examples:
- Comment
- ??? (what else?)
-
Concrete examples:
Key components
- Classes
- Attributes
- Methods
-
Relationships between classes (cardinality)
walkthrough: For dog walking service, how would I show… - Dog walker and client (person)?
- Dogs that he/she is scheduled to walk?
- Relationships?
- Any other classes needed?
Sequence Diagram
Description
-
Shows interactions between objects in a system...
- over time
- for a specific use case
What has to happen before another thing happens? Who is involved?
Key components
- Actors
- Lifelines
- Messages
- Activation boxes
State Diagram
Description
Shows states of a system and how it transitions between them.
Key components
- States
- Transitions
Walkthrough:
State diagram for a light with two switches - one at each end of a hallway.
- Assume light is off with both switches in the off position (initial state).
Activity Diagram
Description
- Models the flow of control from one activity to another.
- Shows logic without implementation detail.
Key components
- Activities
- Transitions
- Branching / merging
- Forking / joining
Hybrids
Swimlane Diagram
- Like an activity diagram... with swimlanes.
- Swimlanes show boundaries between actors / roles in system.
Custom
It’s useful to have a baseline knowledge of UML if you work with software at all. Even rough sketches can save valuable communication time.
Mix and match to suit your needs.