```mermaid
---
config:
  look: classic
  layout: elk
---
classDiagram
        class AirplaneModel {
            Int ModelId
        }
        class Airplane {
            Int AirPlaneId
        }
        class Acquisition {
            Int AcquisitionId
            Float NegotiatedPice
            String Options
            DateTime DeliveryDate
        }
        class Contract {
            Int ContractId
            String Text
        }
        class Employee {
            Int EmployeeId
        }
        class Airline {
            String Name
        }
        AirplaneModel "1..1"--"0..*" Airplane
        Airplane "0..1"--"0..1" Acquisition : part of
        Acquisition "0..*"--"1..1" Contract : part of
        Contract "0..*"--"1..1" Airline
        Contract "0..*"--"1..1" Employee
        Airline "0..1"--"0..*" Airline
```