Alternatives

Alternatives define branching paths from a flow point, rendered as alt/else blocks in sequence diagrams.

Definition

{
  "from": "client",
  "to": "server",
  "action": "authenticate",
  "alternatives": [
    {
      "condition": "invalid_credentials",
      "description": "Authentication failed",
      "flows": [
        {"from": "server", "to": "client", "action": "auth_error", "mode": "response"}
      ]
    },
    {
      "condition": "mfa_required",
      "description": "Multi-factor authentication needed",
      "flows": [
        {"from": "server", "to": "client", "action": "mfa_challenge", "mode": "response"},
        {"from": "client", "to": "server", "action": "mfa_response", "mode": "request"}
      ]
    }
  ]
}

Alternative Fields

Field	Type	Required	Description
condition	string	Yes	Condition that triggers this path
flows	array	Yes	Flows in this alternative path (min 1)
description	string	No	Description of this alternative

Diagram Rendering

Mermaid

sequenceDiagram
    client->>server: authenticate
    alt invalid_credentials
        server-->>client: auth_error
    else mfa_required
        server-->>client: mfa_challenge
        client->>server: mfa_response
    end

PlantUML

client -> server: authenticate
alt invalid_credentials
    server --> client: auth_error
else mfa_required
    server --> client: mfa_challenge
    client -> server: mfa_response
end

Error Handling Pattern

Common pattern for request/response with error handling:

{
  "flows": [
    {
      "from": "client",
      "to": "server",
      "action": "request",
      "alternatives": [
        {
          "condition": "error",
          "flows": [
            {"from": "server", "to": "client", "action": "error_response", "mode": "response"}
          ]
        }
      ]
    },
    {"from": "server", "to": "client", "action": "success_response", "mode": "response"}
  ]
}

Nested Flows

Alternative flows can include all flow features:

{
  "alternatives": [
    {
      "condition": "retry_needed",
      "flows": [
        {
          "from": "client",
          "to": "server",
          "action": "retry",
          "note": "Exponential backoff",
          "annotations": [
            {"type": "performance", "text": "Max 3 retries"}
          ]
        }
      ]
    }
  ]
}

Validation

Alternative flows are validated:

• Condition is required
• At least one flow is required
• Entity references must be valid
• Phase references must be valid (if specified)

Helper Methods (Go)

// Check if flow has alternatives
if flow.HasAlternatives() {
    for _, alt := range flow.Alternatives {
        fmt.Printf("Alternative: %s (%d flows)\n", alt.Condition, len(alt.Flows))
    }
}

vs Condition

Feature	condition	alternatives
Purpose	Single conditional flow	Multiple branching paths
Rendering	opt block	alt/else blocks
Flows	Current flow only	Nested flow arrays

Use condition for "execute this flow if X". Use alternatives for "branch to different paths based on conditions".