Lesson 3: Advanced Scenarios#

In Sruja, the scenario construct is your unified tool for modeling all types of runtime interactions. Whether you are describing a high-level user journey or a low-level technical sequence, scenario handles it all.

One Construct, Many Uses#

Instead of having separate keywords for different types of flows, Sruja allows you to use scenario for:

1. User Flows (The “What”): High-level interactions focusing on value delivery.
2. Technical Sequences (The “How”): Detailed component-to-component interactions.

1. User Flows#

When modeling a user flow, you typically involve person actors and high-level system or container elements. The goal is to show what the user is doing.

// High-level user flow
scenario BuyTicket "User purchases a ticket" {
    User -> WebApp "Selects ticket"
    WebApp -> PaymentService "Process payment"
    PaymentService -> User "Sends receipt"
}

2. Technical Sequences#

When modeling technical sequences, you dive deeper into the architecture, showing how containers and components interact to fulfill a request. This is equivalent to a UML Sequence Diagram.

// Detailed technical flow
scenario AuthFlow "Authentication" "Handles OAuth2 login process" {
    User -> WebApp "Credentials"
    WebApp -> AuthServer "Validate Token"
    AuthServer -> Database "Lookup User"
    Database -> AuthServer "User Data"
    AuthServer -> WebApp "Token Valid"
    WebApp -> User "Login Success"
}

🛠️ Syntax Flexibility#

Sruja offers flexible syntax to suit your needs:

Simple Syntax#

Great for quick sketches or simple flows.

scenario "Login Failure" {
    User -> WebApp "Enters wrong password"
    WebApp -> User "Show error message"
}

Formal Syntax#

Better for documentation and referencing. Includes an ID and optional description.

scenario Checkout "Checkout Process" {
    description "The complete checkout flow including payment and inventory check."
    
    User -> Cart "Checkout"
    Cart -> Inventory "Reserve Items"
    Inventory -> Cart "Reserved"
    Cart -> Payment "Charge"
}

🎨 D2 Layers: Visualizing Views#

Sruja automatically organizes your scenarios into D2 Layers. When you generate a diagram, you don’t just get a static picture; you get an interactive map.

1. Architecture Layer: The base layer showing your static structure (Systems, Containers).
2. Scenario Layers: Each scenario is generated as a separate layer.

This allows you to toggle between the static structure and various runtime flows within the same diagram, giving you a complete 360-degree view of your system!