System requirements
Functional:
List functional requirements for the system (Ask the chat bot for hints if stuck.)...
so we want to be able to reserve a spot, and we want to be able to cancel a spot.
also need a way to receive a ticket or receipt
we need to be able to pay for the parking spot
3 vehicle types: compact, regular, and large vehicle parking spots
- flat rate prices, but 3 different types of parking
should be some mobile app interfacing with backend server
Non-Functional:
List non-functional requirements for the system...
we want to favor consistency over availability because we don't want someone to book a spot that was already taken.
Capacity estimation
Estimate the scale of the system you are going to design...
if we upper bound garage at 10 floors, and there are 200 spots per floor, so 2,000 relevant spots per garage, and with 2,000 relevant spots per garage.
even if 1 million parking garages, this is not in the realm of big data.
we care most about system go up to date with race condition where we allocate two spots at the same time
API design
Define what APIs are expected from the system...
public endpoints:
reserve(parking lot id, space id, start_time, end_time)
we want to return some type of reciept or ticket in a tuple
(spot_id, reservation_id) so we know which reservation we are referring to.
there should be a payment endpoint:
/payment
params:
reservation_id
the actual implementation can be handled by a third party like stripe
we need to be able to cancel reservation, so we need an endpoint for that
/cancel
params:
reservation_id
internal endpoints:
we need a way to calculate individual payments
/calculate_payment
params: reservation_id
reservation id tells us which specific garage and which times
a way to check how many spots are free
/free_spots
check type of vehicle and time because larger spots are able to be used for smaller vehicles, so smaller vehicle can reserver a larger spot in case they run out
/allocate_spot
params:
garage_id, time, vehicle_type
ability to create an account for people using it over and over
/create_acount
params:
password
first name
last name
we can do hashing for that without storing the password in plain text
you could also implement 3rd party single sign on options like google and facebook
/login
params:
password
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...
lean toward relational db for this type of problem as we have structured data. more of my expertise relies in relational db side, so like postgres
reservation table:
id
garage id (foreign_key, int)
spot id (foreign_key, int)
start (timestamp)
end (timestamp)
paid (boolean)
garage table:
zipcode (varchar because we want to accomodate hyphens; also, zipcode helps with sharding down the line)
rate (decimal)
regular rate (decimal)
spots table:
garage id
relevant garage
type of vehicle (enum - trade off when you add enums in a relational db because you become more performant because have benfits of being an int vs. char string, but tradeoff is there's flexbility issues down the line. in postgres, when you add enum, you can't remove the type after adding it, so that's something to consider, but compact regular large won't be out of phase, so this is reasonable to make this an enum)
taken or not (boolean)
users table:
first_name (nullable)
last_name (nullable)
password (convential like sha 256 hash)
Vehicle table:
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?