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Class & ER Diagram Syntax
Class Diagram
Basic Structure
classDiagram
class User {
+String name
+String email
-String passwordHash
+login() bool
+logout()
}
class Order {
+int id
+Date createdAt
+float total
+place()
+cancel()
}
User "1" --> "*" Order : places
Visibility Modifiers
| Symbol |
Meaning |
+ |
Public |
- |
Private |
# |
Protected |
~ |
Package/Internal |
Relationships
| Syntax |
Type |
Meaning |
<|-- |
Inheritance |
extends |
*-- |
Composition |
owns (lifecycle) |
o-- |
Aggregation |
has (independent) |
--> |
Association |
uses |
..> |
Dependency |
depends on |
..|> |
Realization |
implements |
Cardinality
classDiagram
User "1" --> "*" Order : places
Order "1" --> "1..*" OrderItem : contains
Product "0..*" --> "0..*" Category : belongs to
| Notation |
Meaning |
1 |
Exactly one |
0..1 |
Zero or one |
* |
Many |
1..* |
One or more |
n..m |
Range |
ER Diagram
Basic Structure
erDiagram
USER ||--o{ ORDER : places
ORDER ||--|{ ORDER_ITEM : contains
PRODUCT ||--o{ ORDER_ITEM : "included in"
USER {
int id PK
string name
string email
datetime created_at
}
ORDER {
int id PK
int user_id FK
float total
string status
}
ORDER_ITEM {
int order_id FK
int product_id FK
int quantity
}
Relationship Notation
| Left |
Right |
Meaning |
|| |
|| |
One to one |
|| |
o{ |
One to zero or many |
|| |
|{ |
One to one or many |
o| |
o{ |
Zero or one to zero or many |
Attribute Types
erDiagram
PRODUCT {
int id PK "Primary key"
string name "Product name"
float price
int category_id FK "Foreign key"
string sku UK "Unique key"
}
Markers: PK (primary), FK (foreign), UK (unique)
