graph TD
    %% External Clients
    A[Mobile App] -->|REST API| B[API Gateway]
    C[Web Portal] -->|REST API| B

    CS[Config Server]
    SR[Service Registry]
    MQ[[Message Queue]]

    %% Microservices and Databases

    subgraph Subway Service
        G -->|CRUD| G1[(Subway Service DB)]
        G1[("MetroLine,LineSegment,Station,Train,TrainSchedule")]
    end

    subgraph Ticket Service
        I -->|Queries Station| G
        I -->|CRUD| I1[(Ticket Service DB)]
        I1[("P2PJourney,TimedTicketPlan,Ticket,TicketValidation")]
    end

    subgraph Order Service
        J -->|Queries Ticket Plans| I
        J -->|CRUD| J1[(Order Service DB)]
        J1[("TicketOrder,TicketOrderDetail")]
        J -->|Processes Payment| M[External Payment Gateway]
    end

    subgraph Account Service
        E -->|CRUD| E1[(Account Service DB)]
        E1[("Account,DiscountPackage,AccountDiscountPackage,Voucher")]
    end

    %% API Gateway
    B -->|Routes Requests| I[Ticket Service]
    B -->|Routes Requests| G[Subway Service]
    B -->|Routes Requests| J[Order Service]
    B -->|Routes Requests| E[Account Service]

    %% External Payment Gateway
    M -->|Payment Confirmation| J

    J -->|Queries Account & Discount| E

    %% Notes for Clarity
    classDef service fill:#f9f,stroke:#333,stroke-width:2px;
    classDef db fill:#bbf,stroke:#333,stroke-width:2px;
    classDef queue fill:#bbf,stroke:#333,stroke-width:2px;
    classDef external fill:#ffa,stroke:#333,stroke-width:2px;

    class E,G,I,J,SR,B,CS service;
    class MQ queue;
    class E1,G1,I1,J1 db;
    class M external;