UML = blueprint for software. Two types: Structural (class, object diagrams), Behavioral (sequence, activity diagrams)
Identify domain classes (User, Expense), add attributes/methods, draw relationships (1..*
Naming: <<Interface>> | Abstract class | Object
🔗 Types of Relationships
| Relationship | Lines | Meaning |
|---|---|---|
| Association | —— | connection between two classes (1: M), (M: N) E.g., User has Profile. Types: |
——1 (one)
——0…1 (atmost 1)
——* (any)
——1…* (atleast 1) |
| Inheritance | —▶ | or Generalisation |
| Realization | ---▶ | A class implements an interface. |
| Dependency | ---> | uses-a relation. (method param) |
| Aggregation | Team ◇--- Player | has-a relationship. |
| Composition | House ◆--- Room | lives inside relationship |
Helps design structured databases by visually mapping out relationships between data.
Core Components
| Concept | Explanation | Example |
|---|---|---|
| Entity | Object that stores data | Customer, Product, Order |
| Entity Set | Collection of similar entities | All customers in an app |
| Attributes | Properties that describe each entity | email, price, orderDate |
| Primary Key | Uniquely identifies an entity | customer_id, order_id |
| Weak Entity | Depends on another entity, lacks a PK | OrderItem depends on Order |
Relationships can be:
Employee manages another EmployeeDoctor + Patient + Hospital)WorksOn entity with hoursBilled, used in a Billing relationship.| Strategy | Real-World Use Case |
|---|---|
| Specialization | Payment can specialize into CreditCard, PayPal, UPI |
| Generalization | Admin and Customer generalize into a single User type |