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List functional requirements for the system (Ask the chat bot for hints if stuck.)...
List non-functional requirements for the system...
Consistency
Availability
User Experience
Estimate the scale of the system you are going to design...
Define what APIs are expected from the system...
GET /api/v1/cities
Response Code: 200 OK
Response Body : {
"cities": [{
"cityCode": "reston",
"lat": 71.6,
"long": 71.6,
"areas": 10,
"slots": 200000,
"openSlots": "100000"
}, {...}]
}
GET /api/v1/cities/{city}
Response Code: 200 OK
Response Body : {
"areas": [{
"areaCode": "reston-20191",
"areaName": "reston town center",
"lat": 74.6,
"long": 74.6,
"buildings": 10,
"level": 10
"slots": 20000,
"openSlots": "10000"
}, {...}]
}
GET /api/v1/cities/{city}/{area}
Response Code: 200 OK
Response Body : {
"builldings": [{
"buildingCode": "reston-20191-BLD-01",
"lat": 75.6,
"long": 75.6,
"levels": 10,
"slots": 2000,
"openSlots": 1500
}, {...}]
}
GET /api/v1/cities/{city}/{building}
Response Code: 200 OK
Response Body : {
"levels": [{
"levelCode": "reston-20191-BLD-01-LVL-01",
"slots": 200,
"openSlots": 100
}, {...}]
}
GET /api/v1/cities/{city}/{building}/{level}
Response Code: 200 OK
Response Body : {
"slots": [{
"slotCode": "reston-20191-BLD-01-LVL-01-SLT-01",
"disabledAccessiblity": false,
"status": "open"
}, {...}]
}
Reserve a slot
POST /api/v1/reservations
Request Body: {
"levelCode": "reston-20191-BLD-01-LVL-01",
"expectedTime": "1747723584", //Tuesday, 20 May 2025 12:00:00 GMT+05:30,
"vehicle": {
"licensePlate": "ABC",
"size" : "medium",
}
}
Response: 202 Accepted,
Response Body : {
"acknowledgementId": "12345"
"entryTime": "1747723584",
"parkingSlot": {
"slotId": "reston-20191-BLD-01-LVL-01-SLT-01",
"levelCode" : "BLD-01-LVL-01"
}
"status": "allocating" // enum - confirmed, waiting, cancelled
}
POST /api/v1/slots/booking
Request Body: {
"levelCode": "reston-20191-BLD-01-LVL-01",
"entryTime": "1747723584", //Tuesday, 20 May 2025 12:00:00 GMT+05:30,
"vehicle": {
"licensePlate": "ABC",
"size" : "medium",
}
}
Response Code: 201 CREATED, 409 CONFLICT
Response Body: {
"ticketId": "reston-20191-BLD-01-LVL-01-SLT-01-TKT-01",
"entryTime": 1747723584
}
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...
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...
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...
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...
The concept here is to use a Bitmap for each slot for faster writes and low latency reads. The idea is to use a BitMap with 96 bits (12 bytes) for each slot, initially all bits of a slot are 0. How did we get into 96 bits, each day is divided into 15mins intervals i.e. 60 x 24 / 15 = 96 intervals. Each bit represents a 15 min interval, each bitmap represents a day for the slot.
When a vehicle crosses the entry barricade, a booking is made for a slot for an interval, say 1hr from 10:00 AM, four bits from 40 to 43 are set to 1 (booked for 1 hour).
When the vehicle reaches the exit barricade, the kiosk records the exit time, say 11:00 AM, the booking is termed as closed i.e slots from 44 till 96 continues to be 0s.
No Show: When there is booking made for a slot, for the expected time of entry, say 11:00 AM, the respective bit 44 is set to 1. If the vehicle fails to enter the facility (the entry kiosk) before 11:16 AM, the reservation is cancelled and following bits from 45 continues to be 0s, i.e. the slot is blocked only for 15 mins post the expected time of entry. The system may charge 25% percent of 1 hr charge as a fee.
For instance in java,
BitSet slot = new BitSet(96);
public Ticket book(int startInterval, int endInterval) {
slot.set(startInterval, endInterval);
return new Ticket(ticketId, slotDetails);
}
public boolean release(int startInterval, int endInterval) {
slot.clear(startInterval, endInterval);
return true;
}
Explain any trade offs you have made and why you made certain tech choices...
Try to discuss as many failure scenarios/bottlenecks as possible.
What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?