Topics and topic hierarchy in IOT Protocols - Mini Project: Build & Apply

Understanding MQTT Topics and Topic Hierarchy

📖 Scenario: You are working with an MQTT messaging system used in smart home devices. MQTT uses topics to organize messages so devices can subscribe to the right information.Topics are like addresses or folders where messages are sent and received. They have a hierarchy separated by slashes, like home/livingroom/temperature.

🎯 Goal: Learn how to create MQTT topics and understand their hierarchy by building topic strings step-by-step.

📋 What You'll Learn

Create a base topic string for a smart home

Add a room name as a subtopic

Add a sensor type as a subtopic

Print the full topic string

💡 Why This Matters

🌍 Real World

MQTT topics organize messages in IoT systems like smart homes, factories, and vehicles.

💼 Career

Understanding MQTT topics is essential for IoT developers and DevOps engineers managing device communication.

1

Create the base topic

Create a variable called base_topic and set it to the string "home".

IOT Protocols

# Create a variable called base_topic and set it to "home"
# Your code here

Hint

Think of base_topic as the main folder for all smart home messages.

2

Add the room name

Create a variable called room and set it to the string "livingroom". Then create a variable called topic_with_room that joins base_topic and room with a slash / between them.

IOT Protocols

base_topic = "home"
# Create a variable room with value "livingroom"
# Create topic_with_room by joining base_topic and room with '/'
# Your code here

Hint

Use string concatenation with "/" to build the topic hierarchy.

3

Add the sensor type

Create a variable called sensor and set it to the string "temperature". Then create a variable called full_topic that joins topic_with_room and sensor with a slash / between them.

IOT Protocols

base_topic = "home"
room = "livingroom"
topic_with_room = base_topic + "/" + room
# Create a variable sensor with value "temperature"
# Create full_topic by joining topic_with_room and sensor with '/'
# Your code here

Hint

Keep adding levels to the topic by joining strings with slashes.

4

Print the full topic

Write a print statement to display the value of full_topic.

IOT Protocols

base_topic = "home"
room = "livingroom"
topic_with_room = base_topic + "/" + room
sensor = "temperature"
full_topic = topic_with_room + "/" + sensor
# Print the full_topic variable
# Your code here

Hint

Use print(full_topic) to show the complete topic string.

Practice

1. What is the main purpose of topics in IoT protocols like MQTT?

easy

A. To encrypt messages for security

B. To store device firmware

C. To organize messages in a clear, folder-like structure

D. To control device power settings

Solution

1. Step 1: Understand the role of topics

   Topics act like folders to organize messages so devices know where to send or receive data.

2. Step 2: Compare options with topic function

   Only organizing messages matches the purpose of topics; encryption and firmware storage are unrelated.

3. Final Answer:

   To organize messages in a clear, folder-like structure -> Option C

4. Quick Check:

   Topics organize messages = B [OK]

Hint: Topics are like folders for messages [OK]

Common Mistakes:

• Confusing topics with security features
• Thinking topics store device data
• Mixing topics with device settings

2. Which of the following is the correct way to write a topic with three levels?

easy

A. home-kitchen-temperature

B. home.kitchen.temperature

C. home\kitchen\temperature

D. home/kitchen/temperature

Solution

1. Step 1: Recall topic level separator

   Topics use slashes (/) to separate levels, like folders in a path.

2. Step 2: Check each option's separator

   Only home/kitchen/temperature uses slashes correctly; others use dots, backslashes, or dashes which are incorrect.

3. Final Answer:

   home/kitchen/temperature -> Option D

4. Quick Check:

   Topic levels separated by '/' = A [OK]

Hint: Use slashes (/) to separate topic levels [OK]

Common Mistakes:

• Using dots instead of slashes
• Using backslashes which are invalid
• Using dashes instead of separators

3. Given the topic building1/floor2/room3/sensor, which part represents the third level?

medium

A. room3

B. floor2

C. building1

D. sensor

Solution

1. Step 1: Split the topic by slashes

   Splitting 'building1/floor2/room3/sensor' by '/' gives ['building1', 'floor2', 'room3', 'sensor'].

2. Step 2: Identify the third element

   The third element (index 2) is 'room3'.

3. Final Answer:

   room3 -> Option A

4. Quick Check:

   Third level = room3 = C [OK]

Hint: Count levels separated by '/' to find position [OK]

Common Mistakes:

• Counting from zero incorrectly
• Choosing first or second level by mistake
• Confusing last level with third

4. Identify the error in this topic string: home//livingroom/temperature

medium

A. Double slash creates an empty level

B. Missing slash between 'home' and 'livingroom'

C. Topic levels must use dots, not slashes

D. Topic cannot contain the word 'temperature'

Solution

1. Step 1: Analyze the topic string

   The string 'home//livingroom/temperature' has two slashes together, meaning an empty level between them.

2. Step 2: Understand topic level rules

   Empty levels are invalid because each level should have a name; double slashes cause this error.

3. Final Answer:

   Double slash creates an empty level -> Option A

4. Quick Check:

   Double slash = empty level error = A [OK]

Hint: Avoid double slashes to prevent empty topic levels [OK]

Common Mistakes:

• Ignoring empty levels caused by double slashes
• Thinking dots are required separators
• Believing certain words are forbidden in topics

5. You want to subscribe to all sensors in any room on floor 1 of building 2 using MQTT topics. Which subscription topic should you use?

hard

A. building2/floor1/*/sensor

B. building2/floor1/+/sensor

C. building2/floor1/room1/sensor

D. building2/floor1/#/sensor

Solution

1. Step 1: Understand MQTT wildcards

   The '+' wildcard matches exactly one level, while '#' matches all remaining levels.

2. Step 2: Analyze the subscription needs

   We want any room on floor1, so '+' replaces the room level. '#' would match too many levels, and '*' is invalid in MQTT.

3. Final Answer:

   building2/floor1/+/sensor -> Option B

4. Quick Check:

   '+' wildcard for one level = D [OK]

Hint: Use '+' for single-level wildcard in MQTT topics [OK]

Common Mistakes:

• Using '#' when only one level is needed
• Using '*' which is not a valid MQTT wildcard
• Specifying exact room instead of wildcard