Topics and topic hierarchy in IOT Protocols - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to publish a message to the correct MQTT topic.

IOT Protocols

client.publish('[1]', 'Hello World')

Drag options to blanks, or click blank then click option'

Ahome-kitchen-temperature

Bhome/kitchen/temperature

Chome.kitchen.temperature

Dhome_kitchen_temperature

Attempts:

3 left

💡 Hint

Common Mistakes

Using underscores or dots instead of slashes in topic names.

The MQTT topic uses slashes / to separate levels in the topic hierarchy.

2fill in blank

medium

Complete the code to subscribe to all temperature topics under 'home'.

IOT Protocols

client.subscribe('[1]')

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Ahome/temperature/#

Bhome/#/temperature

Chome/temperature/+

Dhome/+/temperature

Attempts:

3 left

💡 Hint

Common Mistakes

Using # in the middle of the topic, which is invalid.

The plus sign + is a single-level wildcard in MQTT topics.

3fill in blank

hard

Fix the error in the topic filter to subscribe to all sensors under 'home'.

IOT Protocols

client.subscribe('[1]')

Drag options to blanks, or click blank then click option'

Ahome/#

Bhome/+/#

Chome/+/+

Dhome/+/sensor/#

Attempts:

3 left

💡 Hint

Common Mistakes

Using # in the middle of the topic filter.

The # wildcard matches all subtopics from the point it is used.

4fill in blank

hard

Fill both blanks to create a topic filter that matches any sensor data in any room under 'home'.

IOT Protocols

client.subscribe('home/[1]/[2]')

Drag options to blanks, or click blank then click option'

A+

B#

Csensor

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using # too early or in the wrong position.

The first + matches any single room, and # matches all subtopics after that.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps sensor names to their latest values from a topic list.

IOT Protocols

sensor_data = { [1]: [2] for [3] in topics if 'sensor' in [3] }

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Atopic.split('/')[-1]

Bvalue

Ctopic

D{topic: value}

Attempts:

3 left

💡 Hint

Common Mistakes

Using the whole topic string as the key instead of the sensor name.

This comprehension extracts the sensor name from the topic string and maps it to its value.

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