C# .NET · MVC · Rules engine · Azure SQL

Car Park Rules Engine

Works out what a parking visit costs and whether it's an overstay, by running the car park's rules in priority order: free parking windows, grace periods, no-return limits, paid time and validation.

Evaluate a parking session

Pick an example or enter your own. Nothing is saved: the session is only checked against the rules.

About this demo

C# MVC on Azure App Service.
Rules and past sessions live in the ParkingEyeCarParks database on Azure SQL server wizzard262.
The rules for car park 1, and how each stored session came out, are on the Rules and sessions page.

The database is on a low-cost tier that sleeps when unused, so the first request can take 30 to 90 seconds.

How the rules work

Each car park has a list of rules, each with a priority.
A rule can apply to every car, or only to a group of registrations, and only in a time window.
The engine checks the rules in priority order; the first one that matches decides the charge.
It also looks up the car's previous exit, so a quick return can break a no-return rule.
The result shows every step it took (the trace).

Architecture for a car park rules engine

Architecture diagram: entry and exit cameras send number plates to Azure Event Hub; Azure Functions match visits and check overstays against rules in SQL Server (with a Redis cache), passing work through Service Bus queues; an external VRN lookup API is polled for keeper details; a penalty service sends letters and emails; logs go to a data lake; operator, admin and public portals sit on an API

Click the diagram to open it full size.