C4 Model Article: Healthcare Appointment Booking System

What is the C4 Model?

The C4 model is a simple, visual way to describe and communicate software architecture. It stands for:

Context – the big picture (who uses the system and what other systems exist around it)
Container – the high-level technical building blocks (web app, mobile app, databases, etc.)
Component – (optional) internal structure of each container
Code – (optional) class/implementation level

It helps teams and stakeholders understand the system at different zoom levels without drowning in details.

Below we apply the first two levels (Context and Container) to a real-world Healthcare Appointment Booking System.

Why do we need this system?

Traditional hospital appointment scheduling is painful:

Patients call during office hours and wait on hold
Staff manually check doctor schedules across paper or fragmented systems
Double-bookings and no-shows are common
No easy way for patients to see their medical summary or join a video consultation
Reminders are forgotten → wasted clinic time

The new Healthcare Appointment Booking System solves these problems by giving patients 24/7 self-service booking, real-time availability, automatic reminders, and integration with telemedicine and EHR.

Who are the main actors?

Actor	Description
Patient	Person needing medical care. Books, reschedules, cancels appointments; joins virtual visits
Healthcare Staff	Doctors, nurses, receptionists who manage schedules and treat patients

Level 1: System Context Diagram

This is the 30,000-foot view

@startuml
!include https://raw.githubusercontent.com/plantuml-stdlib/C4-PlantUML/master/C4_Context.puml

LAYOUT_TOP_DOWN()
LAYOUT_WITH_LEGEND()

title System Context Diagram – Healthcare Appointment Booking System

Person(patient, “Patient”, “Books appointments, joins video visits”)
Person(healthcare_staff, “Healthcare Staff”, “Doctors, nurses, admins”)

System(booking_system, “Healthcare Appointment Booking System”, “Core system for booking, rescheduling, cancelling appointments and virtual consultations”)

System_Ext(ehr_system, “EHR System”, “Electronic Health Records”)
System_Ext(telemedicine_platform, “Telemedicine Platform”, “Video consultation infrastructure”)
System_Ext(schedule_system, “Hospital Schedule System”, “Master calendar of doctors/rooms”)
System_Ext(messaging_system, “Hospital Messaging System”, “SMS/email gateway”)

Rel(patient, booking_system, “Books/reschedules appointments, joins video calls”)
Rel(patient, telemedicine_platform, “Has virtual consultations via”)
Rel(patient, ehr_system, “Views own records (read-only)”)

Rel(healthcare_staff, booking_system, “Manages appointments”)
Rel(healthcare_staff, ehr_system, “Reads/writes patient records”)
Rel(healthcare_staff, schedule_system, “Views master schedule”)
Rel(healthcare_staff, messaging_system, “Sends notifications”)

Rel(booking_system, schedule_system, “Checks & updates real-time availability”)
Rel(booking_system, ehr_system, “Syncs patient identifiers and basic data”)
Rel(booking_system, messaging_system, “Triggers SMS/email reminders”)

@enduml

Key takeaway from Context: Our booking system is the central hub that connects patients, staff, and four existing enterprise systems.

Level 2: Container Diagram

Now we zoom in and show the major technical parts inside our system boundary.

plantuml

Key Containers Explained

Container	Technology	Responsibility
Web Booking Application	React + Node.js/Express	Single page app used by both patients and staff
Mobile App	React Native	Native iOS/Android experience for patients
Telemedicine Module	WebRTC + signaling server	Secure video calls, waiting room, screen sharing
Schedule Engine	Python/Django	Core business logic: no double-bookings, buffer times, holidays
Notification Service	Node.js + Redis + BullMQ	Reliable delivery of reminders 24h, 2h, and 15min before
Patient DB (MySQL)	MySQL 8	Personal data, consent, preferred language
Appointment DB (PostgreSQL)	PostgreSQL 15	Immutable audit trail of all bookings and changes

When do we use each diagram?

Situation	Which diagram to show
Talking to hospital executives or patients	Context diagram (big picture, no tech jargon)
Onboarding new developers	Container diagram (shows where code lives)
Discussing security & compliance boundaries	Container (clear internal vs external systems)
Choosing tech stack or cloud deployment	Container (shows databases, message queues, etc.)
Writing RFP or contract with external vendor	Context + Container

How to Use Visual Paradigm’s AI-Powered Visual Modeling Chatbot to Streamline the Entire C4 Modeling Process for the Healthcare Appointment Booking System

Here’s a real-world, step-by-step workflow that turns hours of manual diagramming and documentation into a 10–15 minute conversation with the AI.

Step 1: Start from Zero with a Single Prompt (30 seconds)

Just type this into Visual Paradigm’s AI chat:

“Create a complete C4 model (Context + Container diagrams) for a modern Healthcare Appointment Booking System. Actors: Patients and Healthcare Staff (doctors, nurses, admins). The system lets patients book, reschedule, and cancel appointments 24/7, join telemedicine video calls, receive automated reminders, and view their own medical summary. It integrates with an existing EHR system, a hospital master schedule system, and a messaging gateway. Use modern tech stack: React web app, React Native mobile app, Node.js backend, Python scheduling engine, PostgreSQL + MySQL databases, WebRTC for video.”

→ In less than 10 seconds you get a beautiful, correctly laid-out C4 Context diagram and C4 Container diagram — almost identical to the PlantUML examples you saw earlier, but already rendered and presentation-ready.

Step 2: Refine Instantly with Natural Commands (2–5 minutes)

Now just chat with the diagram:

“Add a Notification Service container that sends SMS and email reminders”
“Connect the Notification Service to the Hospital Messaging System”
“Show the Telemedicine Module using WebRTC”
“Split the database into Patient DB (MySQL) and Appointment DB (PostgreSQL)”
“Rename ‘Healthcare Staff’ to ‘Doctor / Nurse / Receptionist’ and give it an icon”
“Change the layout to top-down and add a legend”
“Make the Web App and Mobile App both use HTTPS to the backend”

Every command instantly updates the live diagram — no dragging, no re-aligning, no syntax errors.

Step 3: Ask Your Diagram Questions (Instant Insight)

Treat it like a knowledgeable architect sitting next to you:

“What are the external systems this depends on?”
“List all the containers and their technologies”
“What are the main security boundaries?”
“Generate a one-page executive summary of this architecture”
“Write a 3-paragraph description for our RFP”

You immediately get perfectly written text you can copy-paste into proposals, Confluence, or PowerPoint.

Step 4: Get Full Documentation on Demand (30 seconds)

Tell the AI:

“Generate professional architecture documentation for this C4 model, including Context description, Container description, key design decisions, and technology choices.”

You receive a complete, beautifully formatted Markdown or Word-ready document in seconds.

Step 5: One-Click Export to Pro Tool When You Need Team Collaboration

When the design is approved:

Click “Open in Visual Paradigm Desktop” or “Export as .vpp project”
The entire model (with shapes, layout, notes, glossary) opens in the full Visual Paradigm tool for team review, version control, adding Component or Sequence diagrams, generating PDF/PNG, etc.

Why This Is a Game-Changer for the Healthcare Project

Traditional Way (2–8 hours)	With Visual Paradigm AI (10–15 minutes)
Open PlantUML / draw.io / Lucidchart	Just type a paragraph
Manually create every box and arrow	AI creates 95% correct diagram instantly
Fix layout and alignment again and again	AI keeps perfect layout after every edit
Write documentation separately	Ask → get perfect documentation instantly
Copy-paste between tools	One-click seamless handover to full-featured desktop tool

Result: Solution architects, enterprise architects, and development teams can now produce stakeholder-ready C4 diagrams and documentation faster than it takes to schedule the next meeting.

Start now: Go to Visual Paradigm Online → “AI Chat” → paste the prompt above and watch the magic happen in seconds.

Summary

Using just two simple diagrams we can now clearly answer:

What the system does and who benefits
How it fits into the existing hospital IT landscape
What major applications and databases we need to build or integrate

This clarity dramatically reduces misunderstandings between business stakeholders, architects, and development teams — which is exactly why the C4 model has become the de-facto standard for modern software architecture documentation.