System requirements

Functional:

List functional requirements for the system (Ask the chat bot for hints if stuck.)...

1. Show the number of empty spaces

2. Update this number when a user exits

3. If paid service, dispense a ticket on entry and accept payement when user exits

Non-Functional:

List non-functional requirements for the system...

1. Correctness in amount collected from user
2. Correctness in timestamp printed on ticket
3. Highly available
4. Secure in collection and transfer of payment details

Capacity estimation

Estimate the scale of the system you are going to design...

Num Parking Lots: 50 approx

Num Spaces in Each: 300 approx

Num Transactions (entry/exit) per hour in each parking lot = 20

Total num entries or exits across all parking lots per hour = 50 * 20 = 1000

Total num entries or exits across all parking lots per sec = 1000/24 = 50 approx.

API design

Define what APIs are expected from the system...

Internal APIs:

Get all available spaces in a parking lot

GET https://<ip>/emptySpaces?lotId=x

Increment or decrement the number of empty spaces in a parking lot

POST https:///emptyStaces?increment=true/false

Add a parking lot.

POST https:///parkingLot

{

lot_name:

address:

capacity:

rate:

}

Returns:

lotId: L1

Delete/remove a parking lot

DELETE https:///parkingLot?id=L1

Update a parking lot

PUT https:///parkingLot?id=L1

External APIs

Get ticket

GET https:///ticket?lotId=x

Returns:

{

ticketId: T1

lotId: x

timestamp:

validity:

}

Give ticket

POST https:///ticket

{

ticketId: T1

lotId: x

timestamp:

validity:

}

Returns:

Amount Due

Payment Action:

POST https:///makePayment

• After this, payment service provider(PSP) will accept card details etc.

Database design

Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...

SQL Database

High-level design

You should identify enough components that are needed to solve the actual problem from end to end. Also remember to draw a block diagram using the diagramming tool to augment your design. If you are unfamiliar with the tool, you can simply describe your design to the chat bot and ask it to generate a starter diagram for you to modify...

Request flows

Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...

Detailed component design

Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...

Trade offs/Tech choices

Explain any trade offs you have made and why you made certain tech choices...

Failure scenarios/bottlenecks

Try to discuss as many failure scenarios/bottlenecks as possible.

Future improvements

What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?