That repository contains the system analysis and UML diagrams of the car rental business system, e.g., use case diagram, sequence diagrams, Class Responsibilities and Collaborators (CRC) cards, and class diagram.
here is a pdf document of the project requirements and specifications as received from the instructor: Car Rental Business System.
and here is the complete system analysis pdf document: Car Rental Business System Report.
However, for a modifiable document, you can clone your copy of the report on google docs: Car Rental Business System Report.
You can see the UML diagrams in UML diagrams
The project was deliverd as a course project that we have to finish in relatively short time. So if you want to improve it further, you could start the actual software implementation. You can modify the given UML diagrams to suits your project requirements and specifications.