📐 CSS323 — Chapter 4: UML Diagrams Cheat Sheet

1. UML Diagram Taxonomy

UML Diagrams
├── Structure Diagrams
│   ├── Class
│   ├── Object
│   ├── Package
│   ├── Component          ← covered in this chapter
│   ├── Composite Structure
│   └── Deployment         ← covered in this chapter
├── Behavior Diagrams
│   ├── Use Case
│   ├── Activity           ← covered in this chapter (most detail)
│   ├── State Machine      ← covered in this chapter
│   └── Interaction
│       ├── Sequence
│       ├── Communication
│       ├── Interaction Overview
│       └── Timing
└── UML Extension
    └── Profile Diagram

🔵 PART I — Activity Diagrams

2. What Is an Activity Diagram?

Specifies system behavior — shows how data and control flow through a process.

• Based on data flow models — a directed graph showing how data moves through a system
• Think of it as a flowchart on steroids: shows steps AND what data flows between them

🍎 Apple analogy: The "Share Photo" feature in iOS — Activity Diagram shows: tap Share → pick recipient → compress image → send → notify sent. Each step with data flowing between them.

3. Three Node Types (memorize these!)

4. Control Nodes — All 6 Types

Decision vs. Merge — Easy Confusion ⚠️

Decision = one IN, many OUT   (splits based on condition)
Merge    = many IN, one OUT   (combines alternate paths, no waiting)
Fork     = one IN, many OUT   (creates parallel flows, duplicates tokens)
Join     = many IN, one OUT   (synchronizes parallel flows, WAITS)

🍎 Apple analogy:

• Decision: if photoSize > 10MB → compress vs. send directly
• Fork: simultaneously upload to iCloud AND send notification
• Join: wait for BOTH face detection AND location tagging to complete before saving
• Merge: whether user paid by card OR Apple Pay, both paths → "Show Receipt"

5. Edges — Two Types

Edge Weight:

$\boxed{\text{weight} = n \Rightarrow \text{minimum } n \text{ tokens must traverse simultaneously}}$

Example: Form Cricket Team {weight=11} — must have 11 players before the action fires.

6. Actions

The fundamental unit of executable functionality. Does one transformation.

• Creating objects
• Setting attribute values
• Linking objects together
• Invoking behaviors

Pins (inputs/outputs of actions):

Action Start/End Rules:

• Can START when: all non-stream inputs have arrived (or ≥1 stream input if only streams exist)
• Can FINISH when: all inputs arrived + all non-stream/non-exception outputs provided (or an exception output)
• Deadlock prevention: ALL input pins must be ready simultaneously

7. Object Nodes — 4 Types

Object Node Extras:

8. Special Activity Features

Partition (Swimlanes)

• Divides nodes/edges by organizational unit (department, role)
• Can be hierarchical and multidimensional
• Same as BPMN swimlanes

🍎 Apple example: Activity Diagram with swimlanes: Customer lane | iOS App lane | Server lane

Pre & Post Conditions

«precondition» constraint    ← must be true BEFORE activity starts
«postcondition» constraint   ← must be true AFTER activity ends
«localPrecondition»          ← condition on a specific action
«localPostcondition»         ← condition after a specific action

SendSignalAction (pentagon shape)

• Creates and sends a signal asynchronously — no reply expected
• Like sending a text — fire and forget

AcceptEventAction

• Accept event action (concave pentagon) — waits for a signal
• Wait time action (hourglass) — waits for a time event
  • Relative: after (5 seconds)
  • Absolute: Jan, 1, 2000, Noon

InterruptibleActivityRegion (dashed rounded rectangle + ⚡)

• When a token exits via interrupting edge → ALL tokens in region are terminated
• Like an emergency stop button

Exceptions

Protected Node ──[ExceptionType]──▶ Handler Body Node

• If not caught → propagates to enclosing protected node
• If reaches top level uncaught → behavior unspecified

Selection & Transformation on Edges

• Transformation: tokens are converted as they traverse an edge (like a data converter)
• Selection: specifies order tokens are offered from object nodes; edge selection overrides node selection

9. Token Competition

• Object nodes cannot duplicate tokens (unlike Fork nodes)
• Multiple outgoing edges from one object node = competition — only one gets the token
• Results in indeterminacy — which path gets the token is not guaranteed

🟣 PART II — State Machine Diagram

10. What Is a State Machine Diagram?

Shows discrete behavior of an object through finite state transitions.

• Models the lifecycle of ONE object
• State = behavioral condition of an object at a point in time
• Two types: Simple state and Composite state (contains nested sub-states)

11. State Notation — All Elements

State Internal Activities:

StateName
────────────────
entry / entryActivity     ← runs when entering the state
do / doActivity           ← runs continuously while in the state
exit / exitActivity       ← runs when leaving the state

12. State Machine vs. Activity Diagram

🍎 Apple examples:

• Activity: "How does App Store purchase work" → Activity Diagram
• State Machine: "What states does an AirPods connection go through" → Disconnected → Connecting → Connected → Paused → Disconnected

🟢 PART III — Component Diagram

13. What Is a Component Diagram?

Shows components, interfaces, ports, and relationships — used in Component-Based Development (CBD) and Service-Oriented Architecture (SOA).

• Each component = one clear responsibility
• Components interact on a need-to-know basis only

14. Component Stereotypes

15. Component Interfaces — Key Visual Symbols

Provided = what you give (ball sticking out) Required = what you plug into (socket)

16. Two Connector Types

🔴 PART IV — Deployment Diagram

17. What Is a Deployment Diagram?

Shows the physical hardware configuration and how software components are deployed on it.

• Models runtime processing elements
• Only components that exist at runtime appear here
• Used AFTER decisions on: subsystem decomposition, concurrency, hardware/software mapping

18. Key Deployment Diagram Elements

19. Big Picture — Which Diagram for What?