---
id: c4
title: C4
---

## C4 Diagrams

[C4](https://c4model.com/) is a standardized model to visualize software architecture.
You can generate C4 diagrams by using the node and edge classes from the `diagrams.c4` package:

```python
from diagrams import Diagram
from diagrams.c4 import Person, Container, Database, System, SystemBoundary, Relationship

graph_attr = {
    "splines": "spline",
}

with Diagram("Container diagram for Internet Banking System", direction="TB", graph_attr=graph_attr):
    customer = Person(
        name="Personal Banking Customer", description="A customer of the bank, with personal bank accounts."
    )

    with SystemBoundary("Internet Banking System"):
        webapp = Container(
            name="Web Application",
            technology="Java and Spring MVC",
            description="Delivers the static content and the Internet banking single page application.",
        )

        spa = Container(
            name="Single-Page Application",
            technology="Javascript and Angular",
            description="Provides all of the Internet banking functionality to customers via their web browser.",
        )

        mobileapp = Container(
            name="Mobile App",
            technology="Xamarin",
            description="Provides a limited subset of the Internet banking functionality to customers via their mobile device.",
        )

        api = Container(
            name="API Application",
            technology="Java and Spring MVC",
            description="Provides Internet banking functionality via a JSON/HTTPS API.",
        )

        database = Database(
            name="Database",
            technology="Oracle Database Schema",
            description="Stores user registration information, hashed authentication credentials, access logs, etc.",
        )

    email = System(name="E-mail System", description="The internal Microsoft Exchange e-mail system.", external=True)

    mainframe = System(
        name="Mainframe Banking System",
        description="Stores all of the core banking information about customers, accounts, transactions, etc.",
        external=True,
    )

    customer >> Relationship("Visits bigbank.com/ib using [HTTPS]") >> webapp
    customer >> Relationship("Views account balances, and makes payments using") >> [spa, mobileapp]
    webapp >> Relationship("Delivers to the customer's web browser") >> spa
    spa >> Relationship("Make API calls to [JSON/HTTPS]") >> api
    mobileapp >> Relationship("Make API calls to [JSON/HTTPS]") >> api

    api >> Relationship("reads from and writes to") >> database
    api >> Relationship("Sends email using [SMTP]") >> email
    api >> Relationship("Makes API calls to [XML/HTTPS]") >> mainframe
    customer << Relationship("Sends e-mails to") << email
```

It will produce the following diagram:

![c4](/img/c4.png)