UML stands for Unified Modeling Language. It was created to facilitate the communication and documentation of IT designs and architectures. A UML sequence diagram is a type of dynamic behavior diagram that illustrates how objects interact and the sequence of those interactions.

While a UML class diagram depicts the structure of classes and interfaces, a sequence diagram focuses on the processes and interactions between objects or within an object. However, defining a precise sequence diagram can be more complex. It typically contains more elements than a class diagram. As with any tool, it's important to use the sequence diagram for its intended purpose.

For slightly more complex cases, implementing a sequence diagram may require significant effort. Challenges arise when you need to update the diagram, such as adding an object, actor, or new messages in the middle. For these situations, I recommend using DSL-based tools to implement and manage the diagram effectively.

**When to use ✔️**

- ✔️ Planning refactoring

- ✔️ Describing dynamic behavior

- ✔️ Describing processes

- ✔️ Network topology

- ✔️ Event driven designs

- 😐 Identifying relationships

**When to avoid ❌**

- ❌ Designing system architecture

- ❌ Documenting the system architecture

- ❌ Database schema design

- ❌ Large systems

- ❌ Static structure

- ❌ Exposing too much implementation details

UML - Sequence Diagram

UML stands for Unified Modeling Language. It was created to communicate and document IT designs and architecture. UML class diagram is a static structure diagram, that describes interfaces, classes, attributes and methods, and relationships between.

What I like about UML class diagram, that the complexity in the diagram itself is optional. You can omit the attributes and methods if you think, that they will not serve the purpose of conducting the information that you want to share with this chart. In other situation, you can be very explicit defining all attributes, relations and cardinalities if the problem domain is small and chart can be explicit. With UML class diagram you can create a documentation or design artifact, that will be better that 100 words and better than code. Because of ease of use UML class diagram can be used as a bridge communicating complex designs to a non technical users, stakeholders.

**When to use ✔️**

- ✔️ Designing system architecture

- ✔️ Documenting the system architecture

- ✔️ Database schema design

- ✔️ Identifying relationships

- ✔️ Planning refactoring

**When to avoid ❌**

- ❌ Describing dynamic behavior

- ❌ Describing processes

- ❌ Network topology

- ❌ Large systems

- ❌ Event driven designs

Code form the charts:

```typescript
export class Customer {
    constructor(
        public customerId: number,
        public name: string
        ) {}
}
export interface Order {
     orderId: number,
     totalAmount: number,
     customer: Customer
}
export abstract class BaseOrder implements Order {
    constructor(
        public orderId: number,
        public totalAmount: number,
        public customer: Customer
        ) {}
}
export class BookOrder extends BaseOrder {
    constructor(
        orderId: number,
        totalAmount: number,
        customer: Customer,
        private isbn: string

    ) {
        super(orderId, totalAmount, customer);
    }
}
export class Employee {
    private name: string;

    constructor(employeeId: number, name: string) {
        this.name = name;
    }
    processOrder(order: Order): void {}
}
export class Department {
    constructor(
        employees: Employee[]
    ) {}
}
export class OrganizationalStructure {
    constructor(
        departments: Department[]
    ) {}
}
```